Incredible shrinking material: Engineers reveal how scandium trifluoride contracts with heat

ScienceDaily (Nov. 7, 2011) — They shrink when you heat 'em. Most materials expand when heated, but a few contract. Now engineers at the California Institute of Technology (Caltech) have figured out how one of these curious materials, scandium trifluoride (ScF3), does the trick -- a finding, they say, that will lead to a deeper understanding of all kinds of materials.

The researchers, led by graduate student Chen Li, published their results in the November 4 issue of Physical Review Letters (PRL).

Materials that don't expand under heat aren't just an oddity. They're useful in a variety of applications -- in mechanical machines such as clocks, for example, that have to be extremely precise. Materials that contract could counteract the expansion of more conventional ones, helping devices remain stable even when the heat is on.

"When you heat a solid, most of the heat goes into the vibrations of the atoms," explains Brent Fultz, professor of materials science and applied physics and a coauthor of the paper. In normal materials, this vibration causes atoms to move apart and the material to expand. A few of the known shrinking materials, however, have unique crystal structures that cause them to contract when heated, a property called negative thermal expansion. But because these crystal structures are complicated, scientists have not been able to clearly see how heat -- in the form of atomic vibrations -- could lead to contraction.

But in 2010 researchers discovered negative thermal expansion in ScF3, a powdery substance with a relatively simple crystal structure. To figure out how its atoms vibrated under heat, Li, Fultz, and their colleagues used a computer to simulate each atom's quantum behavior. The team also probed the material's properties by blasting it with neutrons at the Spallation Neutron Source at Oak Ridge National Laboratory (ORNL) in Tennessee; by measuring the angles and speeds with which the neutrons scattered off the atoms in the crystal lattice, the team could study the atoms' vibrations. The more the material is heated the more it contracts, so by doing this scattering experiment at increasing temperatures, the team learned how the vibrations changed as the material shrank.

The results paint a clear picture of how the material shrinks, the researchers say. You can imagine the bound scandium and fluorine atoms as balls attached to one another with springs. The lighter fluorine atom is linked to two heavier scandium atoms on opposite sides. As the temperature is cranked up, all the atoms jiggle in many directions. But because of the linear arrangement of the fluorine and two scandiums, the fluorine vibrates more in directions perpendicular to the springs. With every shake, the fluorine pulls the scandium atoms toward each other. Since this happens throughout the material, the entire structure shrinks.

The surprise, the researchers say, was that in the large fluorine vibrations, the energy in the springs is proportional to the atom's displacement -- how far the atom moves while shaking -- raised to the fourth power, a behavior known as a quartic oscillation. Most materials are dominated by quadratic (or harmonic) oscillations -- characteristic of the typical back-and-forth motion of springs and pendulums -- in which the stored energy is proportional to the square of the displacement.

"A nearly pure quantum quartic oscillator has never been seen in atom vibrations in crystals," Fultz says. Many materials have a little bit of quartic behavior, he explains, but their quartic tendencies are pretty small. In the case of ScF3, however, the team observed the quartic behavior very clearly. "A pure quartic oscillator is a lot of fun," he says. "Now that we've found a case that's very pure, I think we know where to look for it in many other materials." Understanding quartic oscillator behavior will help engineers design materials with unusual thermal properties. "In my opinion," Fultz says, "that will be the biggest long-term impact of this work."

The other authors of the PRL paper, "The structural relationship between negative thermal expansion and quartic anharmonicity of cubic ScF3," are former Caltech postdoctoral scholars Xiaoli Tang and J. Brandon Keith; Caltech graduate students Jorge Muñoz and Sally Tracy; and Doug Abernathy of ORNL. The research was supported by the Department of Energy.

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted from materials provided by California Institute of Technology. The original article was written by Marcus Woo.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Observations of gamma-ray burst reveal surprising ingredients of early galaxies

ScienceDaily (Nov. 2, 2011) — An international team of astronomers led by the Max Planck Institute for Extraterrestrial Physics has used the brief but brilliant light of a distant gamma-ray burst as a probe to study the make-up of very distant galaxies. Surprisingly the new observations revealed two galaxies in the young Universe that are richer in the heavier chemical elements than the Sun. The two galaxies may be in the process of merging. Such events in the early Universe will drive the formation of many new stars and may be the trigger for gamma-ray bursts.

Gamma-ray bursts are the brightest explosions in the Universe. They are first spotted by orbiting observatories that detect the initial short burst of gamma rays. After their positions have been pinned down, they are then immediately studied using large ground-based telescopes that can detect the visible-light and infrared afterglows that the bursts emit over the succeeding hours and days. One such burst, called GRB 090323, was first spotted by the NASA Fermi Gamma-ray Space Telescope. Very soon afterwards it was picked up by the X-ray detector on NASA's Swift satellite and with the GROND system at the MPG/ESO 2.2-metre telescope in Chile. From the GROND observations, the astronomers estimated the minimum rate of star formation, which has to be several times higher than the one in our Galaxy. They could, however, only determine a minimum value because the detected emission could be heavily affected (i.e. absorbed) by the presence of dust in the galaxies. The real rate of star formation, once the (unknown) dust absorption has been taken into account, could easily be 50 times higher than in the Milky Way.

The burst was also studied in great detail using ESO's Very Large Telescope (VLT) just one day after it exploded. These observations show that the brilliant light from the gamma-ray burst had passed through its own host galaxy and another galaxy nearby. These galaxies are being seen as they were about 12 billion years ago. Such distant galaxies are very rarely caught in the glare of a gamma-ray burst.

"When we studied the light from this gamma-ray burst we didn't know what we might find. It was a surprise that the cool gas in these two galaxies in the early Universe proved to have such an unexpected chemical make-up," explains Sandra Savaglio (Max-Planck Institute for Extraterrestrial Physics, Garching, Germany), lead author of the paper describing the new results. "These galaxies have more heavy elements than have ever been seen in a galaxy so early in the evolution of the Universe. We didn't expect the Universe to be so mature, so chemically evolved, so early on."

As light from the gamma-ray burst passed through the galaxies, the gas there acted like a filter, and absorbed some of the light from the gamma-ray burst at certain wavelengths. Without the gamma-ray burst these faint galaxies would be invisible. By carefully analysing the tell-tale fingerprints from different chemical elements the team was able to work out the composition of the cool gas in these very distant galaxies, and in particular how rich they were in heavy elements.

It is expected that galaxies in the young Universe will be found to contain smaller amounts of heavier elements than galaxies at the present day, such as the Milky Way. The heavier elements are produced during the lives and deaths of generations of stars, gradually enriching the gas in the galaxies. Astronomers can use the chemical enrichment in galaxies to indicate how far they are through their lives. But the new observations, surprisingly, revealed that some galaxies were already very rich in heavy elements less than two billion years after the Big Bang. Something unthinkable until recently.

The newly discovered pair of young galaxies must be forming new stars at a tremendous rate, to enrich the cool gas so strongly and quickly. As the two galaxies are close to each other they may be in the process of merging, which would also provoke star formation when the gas clouds collide. The new results also support the idea that gamma-ray bursts may be associated with vigorous massive star formation.

Energetic star formation in galaxies like these might have ceased early on in the history of the Universe. Twelve billion years later, at the present time, the remains of such galaxies would contain a large number of stellar remnants such as black holes and cool dwarf stars, forming a hard to detect population of "dead galaxies," just faint shadows of how they were in their brilliant youths. Finding such corpses in the present day would be a challenge.

"We were very lucky to observe GRB 090323 when it was still sufficiently bright, so that it was possible to obtain spectacularly detailed observations with the VLT. Gamma-ray bursts only stay bright for a very short time and getting good quality data is very hard. We hope to observe these galaxies again in the future when we have much more sensitive instruments, they would make perfect targets for the E-ELT," concludes Savaglio.

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted from materials provided by Max-Planck-Institut für extraterrestrische Physik (MPE).

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

S. Savaglio et al. Super-solar Metal Abundances in Two Galaxies at z~3.57 revealed by the GRB090323 Afterglow Spectrum. Monthly Notices of the Royal Astronomical Society, 2011

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Chemists reveal the force within you: New method for visualizing mechanical forces on cell surface

ScienceDaily (Nov. 9, 2011) — A new method for visualizing mechanical forces on the surface of a cell, reported in Nature Methods, provides the first detailed view of those forces, as they occur in real-time.

"Now we're able to measure something that's never been measured before: The force that one molecule applies to another molecule across the entire surface of a living cell, and as this cell moves and goes about its normal processes," says Khalid Salaita, assistant professor of biomolecular chemistry at Emory University. "And we can visualize these forces in a time-lapsed movie."

Salaita developed the florescent-sensor technique with chemistry graduate students Daniel Stabley and Carol Jurchenko, and undergraduate senior Stephen Marshall.

"Cells are constantly tugging and pushing on their surroundings, and they can even communicate with one another using mechanics," Salaita says. "One way that cells use forces is evident from the characteristic architecture of tissue, like a lung or a heart. If we want to really understand cells and how they work, we have to understand cell mechanics at a molecular level. The first step is to measure the tension applied to specific receptors on the cell surface."

The researchers demonstrated their technique on the epidermal growth factor receptor (EGFR), one of the most studied cellular signaling pathways. They mapped the mechanical strain exerted by EGFR during the early stages of endocytosis, when the protein receptor of a cell takes in a ligand, or binding molecule. The results showed that the cell does not passively absorb the ligand, but physically pulls it inside during the process. Their experiments provide the first direct evidence that force is exerted during endocytosis.

Mapping such forces may help to diagnose and treat diseases related to cellular mechanics. Cancer cells, for instance, move differently from normal cells, and it is unclear whether that difference is a cause or an effect of the disease.

"It's known that if EGFR is over-active, that can lead to cancer," Salaita says. "And one of the ways that EGFR is activated is by binding its ligand and taking it in. So if we can understand how tugging on EGFR force changes the pathway, and whether it plays a role in cancer, it might be possible to design drugs that target this pulling process."

Several methods have been developed in recent years to try to study the mechanics of cellular forces, but they have major limitations.

One genetic engineering approach requires splitting open and modifying proteins of a cell. This invasive technique may change the behavior of the cell, skewing the results.

The technique developed at Emory is non-invasive, does not modify the cell, and can be done with a standard fluorescence microscope. A flexible polymer is chemically modified at both ends. One end gets a fluorescence-based turn-on sensor that will bind to a receptor on the cell surface. The other end is chemically anchored to a microscope slide and a molecule that quenches fluorescence.

"Once a force is applied to the polymer, it stretches out," Salaita explains. "And as it extends, the distance from the quencher increases and the fluorescent signal turns on and grows brighter. We can determine the force being exerted by measuring the amount of fluorescent light emitted."

The forces of any individual protein or molecule on the cell surface can be measured using the technique, at far higher spatial and temporal resolutions than was previously possible.

Many mysteries beyond the biology and chemistry of cells may be explained through measuring cellular forces. How does a cancer cell crawl when a tumor spreads? What are the forces involved in cell division and immune response? What are the mechanics that allow groups of cardiac cells to beat in unison?

"Our method can be applied to nearly any receptor, opening the door to rapidly studying chemical and mechanical interactions across the thousands of membrane-bound receptors on the surface of virtually any cell type," Salaita says. "We hope that measuring cellular forces could then become part of the standard repertoire of biochemical techniques that scientists use to study living systems."

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted from materials provided by Emory University. The original article was written by Carol Clark.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Daniel R Stabley, Carol Jurchenko, Stephen S Marshall, Khalid S Salaita. Visualizing mechanical tension across membrane receptors with a fluorescent sensor. Nature Methods, 2011; DOI: 10.1038/nmeth.1747

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Chemists reveal the force within you: New method for visualizing mechanical forces on cell surface

ScienceDaily (Nov. 9, 2011) — A new method for visualizing mechanical forces on the surface of a cell, reported in Nature Methods, provides the first detailed view of those forces, as they occur in real-time.

"Now we're able to measure something that's never been measured before: The force that one molecule applies to another molecule across the entire surface of a living cell, and as this cell moves and goes about its normal processes," says Khalid Salaita, assistant professor of biomolecular chemistry at Emory University. "And we can visualize these forces in a time-lapsed movie."

Salaita developed the florescent-sensor technique with chemistry graduate students Daniel Stabley and Carol Jurchenko, and undergraduate senior Stephen Marshall.

"Cells are constantly tugging and pushing on their surroundings, and they can even communicate with one another using mechanics," Salaita says. "One way that cells use forces is evident from the characteristic architecture of tissue, like a lung or a heart. If we want to really understand cells and how they work, we have to understand cell mechanics at a molecular level. The first step is to measure the tension applied to specific receptors on the cell surface."

The researchers demonstrated their technique on the epidermal growth factor receptor (EGFR), one of the most studied cellular signaling pathways. They mapped the mechanical strain exerted by EGFR during the early stages of endocytosis, when the protein receptor of a cell takes in a ligand, or binding molecule. The results showed that the cell does not passively absorb the ligand, but physically pulls it inside during the process. Their experiments provide the first direct evidence that force is exerted during endocytosis.

Mapping such forces may help to diagnose and treat diseases related to cellular mechanics. Cancer cells, for instance, move differently from normal cells, and it is unclear whether that difference is a cause or an effect of the disease.

"It's known that if EGFR is over-active, that can lead to cancer," Salaita says. "And one of the ways that EGFR is activated is by binding its ligand and taking it in. So if we can understand how tugging on EGFR force changes the pathway, and whether it plays a role in cancer, it might be possible to design drugs that target this pulling process."

Several methods have been developed in recent years to try to study the mechanics of cellular forces, but they have major limitations.

One genetic engineering approach requires splitting open and modifying proteins of a cell. This invasive technique may change the behavior of the cell, skewing the results.

The technique developed at Emory is non-invasive, does not modify the cell, and can be done with a standard fluorescence microscope. A flexible polymer is chemically modified at both ends. One end gets a fluorescence-based turn-on sensor that will bind to a receptor on the cell surface. The other end is chemically anchored to a microscope slide and a molecule that quenches fluorescence.

"Once a force is applied to the polymer, it stretches out," Salaita explains. "And as it extends, the distance from the quencher increases and the fluorescent signal turns on and grows brighter. We can determine the force being exerted by measuring the amount of fluorescent light emitted."

The forces of any individual protein or molecule on the cell surface can be measured using the technique, at far higher spatial and temporal resolutions than was previously possible.

Many mysteries beyond the biology and chemistry of cells may be explained through measuring cellular forces. How does a cancer cell crawl when a tumor spreads? What are the forces involved in cell division and immune response? What are the mechanics that allow groups of cardiac cells to beat in unison?

"Our method can be applied to nearly any receptor, opening the door to rapidly studying chemical and mechanical interactions across the thousands of membrane-bound receptors on the surface of virtually any cell type," Salaita says. "We hope that measuring cellular forces could then become part of the standard repertoire of biochemical techniques that scientists use to study living systems."

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted from materials provided by Emory University. The original article was written by Carol Clark.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Daniel R Stabley, Carol Jurchenko, Stephen S Marshall, Khalid S Salaita. Visualizing mechanical tension across membrane receptors with a fluorescent sensor. Nature Methods, 2011; DOI: 10.1038/nmeth.1747

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Distant galaxies reveal the clearing of the cosmic fog; New VLT observations chart timeline of reionization

ScienceDaily (Oct. 13, 2011) — An international team of astronomers used the VLT as a time machine, to look back into the early Universe and observe several of the most distant galaxies ever detected. They have been able to measure their distances accurately and find that we are seeing them as they were between 780 million and a billion years after the Big Bang [1].

The new observations have allowed astronomers to establish a timeline for what is known as the age of reionisation [2] for the first time. During this phase the fog of hydrogen gas in the early Universe was clearing, allowing ultraviolet light to pass unhindered for the first time.

The new results, which will appear in the Astrophysical Journal, build on a long and systematic search for distant galaxies that the team has carried out with the VLT over the last three years.

"Archaeologists can reconstruct a timeline of the past from the artifacts they find in different layers of soil. Astronomers can go one better: we can look directly into the remote past and observe the faint light from different galaxies at different stages in cosmic evolution," explains Adriano Fontana, of INAF Rome Astronomical Observatory who led this project. "The differences between the galaxies tell us about the changing conditions in the Universe over this important period, and how quickly these changes were occurring."

Different chemical elements glow brightly at characteristic colours. These spikes in brightness are known as emission lines. One of the strongest ultraviolet emission lines is the Lyman-alpha line, which comes from hydrogen gas [3]. It is bright and recognisable enough to be seen even in observations of very faint and faraway galaxies.

Spotting the Lyman-alpha line for five very distant galaxies [4] allowed the team to do two key things: first, by observing how far the line had been shifted toward the red end of the spectrum, they were able to determine the galaxies' distances, and hence how soon after the Big Bang they could see them [5]. This let them place them in order, creating a timeline which shows how the galaxies' light evolved over time. Secondly, they were able to see the extent to which the Lyman-alpha emission -- which comes from glowing hydrogen within the galaxies -- was reabsorbed by the neutral hydrogen fog in intergalactic space at different points in time.

"We see a dramatic difference in the amount of ultraviolet light that was blocked between the earliest and latest galaxies in our sample," says lead author Laura Pentericci of INAF Rome Astronomical Observatory. "When the Universe was only 780 million years old this neutral hydrogen was quite abundant, filling from 10 to 50% of the Universe' volume. But only 200 million years later the amount of neutral hydrogen had dropped to a very low level, similar to what we see today. It seems that reionisation must have happened quicker than astronomers previously thought."

As well as probing the rate at which the primordial fog cleared, the team's observations also hint at the likely source of the ultraviolet light which provided the energy necessary for reionisation to occur. There are several competing theories for where this light came from -- two leading candidates are the Universe's first generation of stars [6], and the intense radiation emitted by matter as it falls towards black holes.

"The detailed analysis of the faint light from two of the most distant galaxies we found suggests that the very first generation of stars may have contributed to the energy output observed," says Eros Vanzella of the INAF Trieste Observatory, a member of the research team. "These would have been very young and massive stars, about five thousand times younger and one hundred times more massive than the Sun, and they may have been able to dissolve the primordial fog and make it transparent."

The highly accurate measurements required to confirm or disprove this hypothesis, and show that the stars can produce the required energy, require observations from space, or from ESO's planned European Extremely Large Telescope, which will be the world's largest eye on the sky once completed early next decade.

Studying this early period in cosmic history is technically challenging because accurate observations of extremely distant and faint galaxies are needed, a task which can only be attempted with the most powerful telescopes. For this study, the team used the great light-gathering power of the 8.2-metre VLT to carry out spectroscopic observations, targetting galaxies first identified by the NASA/ESA Hubble Space Telescope and in deep images from the VLT.

Notes

[1] The most distant galaxy that has been reported with a distance measured by spectroscopy is at a redshift of 8.6, placing it 600 million years after the Big Bang (eso1041). There is a candidate galaxy thought to be at a redshift of about 10 (480 million years after the Big Bang) identified by the Hubble Space Telescope, but this is awaiting confirmation. The most distant galaxy in this study is at a redshift of 7.1, placing it 780 million years after the Big Bang. The Universe today is 13.7 billion years old. The new sample of five confirmed galaxies with Lyman-alpha detections (out of 20 candidates) includes half of all galaxies known at z>7.

[2] At the time the first stars and galaxies formed, the Universe was filled with electrically neutral hydrogen gas, which absorbs ultraviolet light. As the ultraviolet radiation from these early galaxies excited the gas, making it electrically charged (ionised), it gradually became transparent to ultraviolet light. This process is technically known as reionisation, as there is thought to have been a brief period within the first 100 000 years after the Big Bang in which the hydrogen was also ionised.

[3] The team measured the effects of the hydrogen fog using spectroscopy, a technique which involves splitting and spreading out the light from the galaxy into its component colours, much like a prism splits sunlight into a rainbow.

[4] The team used the VLT to study the spectra of 20 candidate galaxies at redshifts close to 7. These come from deep imaging studies of three separate fields. Of these 20 targets five were found to have clearly detected Lyman-alpha emission. This is currently the only set of spectroscopically confirmed galaxies around z=7.

[5] Because the Universe is expanding, the wavelength of light from objects gets stretched as it passes through space. The further light has to travel, the more its wavelength is stretched. As red is the longest wavelength visible to our eyes, the characteristic red colour this gives to extremely distant objects has become known as 'redshift'. Although it is technically a measure of how the colour of an object's light has been affected, it is also by extension a measure both of the object's distance, and of how long after the Big Bang we see it.

[6] Astronomers classify stars into three categories, known as Population I, Population II and Population III. Population I stars, like our Sun, are rich in heavier elements synthesised in the hearts of older stars and in supernova explosions: as they are made up from the wreckage of previous generations of stars, they only came into existence later in the Universe. Population II stars have fewer heavy elements in them and are predominantly made up of the hydrogen, helium and lithium created during the Big Bang. These are older stars, though there are still many of them in existence in the Universe today. Population III stars have never been directly observed, though they are thought to have existed in the early years of the Universe. As these contained only the material created during the Big Bang, they contained no heavier elements at all. Because of the role of heavier elements in the formation of stars, only very large stars with very short lifespans were able to form at this stage, and so all the Population III stars quickly ended their lives in supernovae in the early years of the Universe. Up to now, no solid evidence of Population III stars has been confirmed even in observations of very distant galaxies.

More information

This research was presented in a paper "Spectroscopic Confirmation of z7 LBGs: Probing the Earliest Galaxies and the Epoch of Reionization," to appear in the Astrophysical Journal.

The team is composed of L.Pentericci (INAF Osservatorio Astronomico di Roma, Rome, Italy [INAF-OAR]), A. Fontana (INAF-OAR), E. Vanzella (INAF Osservatorio Astronomico di Trieste, Trieste, Italy [INAF-OAT]), M. Castellano (INAF-OAR), A. Grazian (INAF-OAR), M. Dijkstra (Max-Planck-Institut fur Astrophysik, Garching, Germany), K. Boutsia (INAF-OAR), S. Cristiani (INAF-OAT), M. Dickinson (National Optical Astronomy Observatory, Tucson, USA), E. Giallongo (INAF-OAR), M. Giavalisco (University of Massachusetts, Amherst, USA), R. Maiolino (INAF-OAR), A. Moorwood (ESO, Garching), P. Santini (INAF-OAR).

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by European Southern Observatory - ESO.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Distant galaxies reveal the clearing of the cosmic fog; New VLT observations chart timeline of reionization

ScienceDaily (Oct. 13, 2011) — An international team of astronomers used the VLT as a time machine, to look back into the early Universe and observe several of the most distant galaxies ever detected. They have been able to measure their distances accurately and find that we are seeing them as they were between 780 million and a billion years after the Big Bang [1].

The new observations have allowed astronomers to establish a timeline for what is known as the age of reionisation [2] for the first time. During this phase the fog of hydrogen gas in the early Universe was clearing, allowing ultraviolet light to pass unhindered for the first time.

The new results, which will appear in the Astrophysical Journal, build on a long and systematic search for distant galaxies that the team has carried out with the VLT over the last three years.

"Archaeologists can reconstruct a timeline of the past from the artifacts they find in different layers of soil. Astronomers can go one better: we can look directly into the remote past and observe the faint light from different galaxies at different stages in cosmic evolution," explains Adriano Fontana, of INAF Rome Astronomical Observatory who led this project. "The differences between the galaxies tell us about the changing conditions in the Universe over this important period, and how quickly these changes were occurring."

Different chemical elements glow brightly at characteristic colours. These spikes in brightness are known as emission lines. One of the strongest ultraviolet emission lines is the Lyman-alpha line, which comes from hydrogen gas [3]. It is bright and recognisable enough to be seen even in observations of very faint and faraway galaxies.

Spotting the Lyman-alpha line for five very distant galaxies [4] allowed the team to do two key things: first, by observing how far the line had been shifted toward the red end of the spectrum, they were able to determine the galaxies' distances, and hence how soon after the Big Bang they could see them [5]. This let them place them in order, creating a timeline which shows how the galaxies' light evolved over time. Secondly, they were able to see the extent to which the Lyman-alpha emission -- which comes from glowing hydrogen within the galaxies -- was reabsorbed by the neutral hydrogen fog in intergalactic space at different points in time.

"We see a dramatic difference in the amount of ultraviolet light that was blocked between the earliest and latest galaxies in our sample," says lead author Laura Pentericci of INAF Rome Astronomical Observatory. "When the Universe was only 780 million years old this neutral hydrogen was quite abundant, filling from 10 to 50% of the Universe' volume. But only 200 million years later the amount of neutral hydrogen had dropped to a very low level, similar to what we see today. It seems that reionisation must have happened quicker than astronomers previously thought."

As well as probing the rate at which the primordial fog cleared, the team's observations also hint at the likely source of the ultraviolet light which provided the energy necessary for reionisation to occur. There are several competing theories for where this light came from -- two leading candidates are the Universe's first generation of stars [6], and the intense radiation emitted by matter as it falls towards black holes.

"The detailed analysis of the faint light from two of the most distant galaxies we found suggests that the very first generation of stars may have contributed to the energy output observed," says Eros Vanzella of the INAF Trieste Observatory, a member of the research team. "These would have been very young and massive stars, about five thousand times younger and one hundred times more massive than the Sun, and they may have been able to dissolve the primordial fog and make it transparent."

The highly accurate measurements required to confirm or disprove this hypothesis, and show that the stars can produce the required energy, require observations from space, or from ESO's planned European Extremely Large Telescope, which will be the world's largest eye on the sky once completed early next decade.

Studying this early period in cosmic history is technically challenging because accurate observations of extremely distant and faint galaxies are needed, a task which can only be attempted with the most powerful telescopes. For this study, the team used the great light-gathering power of the 8.2-metre VLT to carry out spectroscopic observations, targetting galaxies first identified by the NASA/ESA Hubble Space Telescope and in deep images from the VLT.

Notes

[1] The most distant galaxy that has been reported with a distance measured by spectroscopy is at a redshift of 8.6, placing it 600 million years after the Big Bang (eso1041). There is a candidate galaxy thought to be at a redshift of about 10 (480 million years after the Big Bang) identified by the Hubble Space Telescope, but this is awaiting confirmation. The most distant galaxy in this study is at a redshift of 7.1, placing it 780 million years after the Big Bang. The Universe today is 13.7 billion years old. The new sample of five confirmed galaxies with Lyman-alpha detections (out of 20 candidates) includes half of all galaxies known at z>7.

[2] At the time the first stars and galaxies formed, the Universe was filled with electrically neutral hydrogen gas, which absorbs ultraviolet light. As the ultraviolet radiation from these early galaxies excited the gas, making it electrically charged (ionised), it gradually became transparent to ultraviolet light. This process is technically known as reionisation, as there is thought to have been a brief period within the first 100 000 years after the Big Bang in which the hydrogen was also ionised.

[3] The team measured the effects of the hydrogen fog using spectroscopy, a technique which involves splitting and spreading out the light from the galaxy into its component colours, much like a prism splits sunlight into a rainbow.

[4] The team used the VLT to study the spectra of 20 candidate galaxies at redshifts close to 7. These come from deep imaging studies of three separate fields. Of these 20 targets five were found to have clearly detected Lyman-alpha emission. This is currently the only set of spectroscopically confirmed galaxies around z=7.

[5] Because the Universe is expanding, the wavelength of light from objects gets stretched as it passes through space. The further light has to travel, the more its wavelength is stretched. As red is the longest wavelength visible to our eyes, the characteristic red colour this gives to extremely distant objects has become known as 'redshift'. Although it is technically a measure of how the colour of an object's light has been affected, it is also by extension a measure both of the object's distance, and of how long after the Big Bang we see it.

[6] Astronomers classify stars into three categories, known as Population I, Population II and Population III. Population I stars, like our Sun, are rich in heavier elements synthesised in the hearts of older stars and in supernova explosions: as they are made up from the wreckage of previous generations of stars, they only came into existence later in the Universe. Population II stars have fewer heavy elements in them and are predominantly made up of the hydrogen, helium and lithium created during the Big Bang. These are older stars, though there are still many of them in existence in the Universe today. Population III stars have never been directly observed, though they are thought to have existed in the early years of the Universe. As these contained only the material created during the Big Bang, they contained no heavier elements at all. Because of the role of heavier elements in the formation of stars, only very large stars with very short lifespans were able to form at this stage, and so all the Population III stars quickly ended their lives in supernovae in the early years of the Universe. Up to now, no solid evidence of Population III stars has been confirmed even in observations of very distant galaxies.

More information

This research was presented in a paper "Spectroscopic Confirmation of z7 LBGs: Probing the Earliest Galaxies and the Epoch of Reionization," to appear in the Astrophysical Journal.

The team is composed of L.Pentericci (INAF Osservatorio Astronomico di Roma, Rome, Italy [INAF-OAR]), A. Fontana (INAF-OAR), E. Vanzella (INAF Osservatorio Astronomico di Trieste, Trieste, Italy [INAF-OAT]), M. Castellano (INAF-OAR), A. Grazian (INAF-OAR), M. Dijkstra (Max-Planck-Institut fur Astrophysik, Garching, Germany), K. Boutsia (INAF-OAR), S. Cristiani (INAF-OAT), M. Dickinson (National Optical Astronomy Observatory, Tucson, USA), E. Giallongo (INAF-OAR), M. Giavalisco (University of Massachusetts, Amherst, USA), R. Maiolino (INAF-OAR), A. Moorwood (ESO, Garching), P. Santini (INAF-OAR).

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by European Southern Observatory - ESO.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Orbital observations of Mercury reveal flood lavas, hollows, and unprecedented surface details

ScienceDaily (Sep. 29, 2011) — After only six months in orbit around Mercury, NASA's MESSENGER spacecraft is sending back information that has revolutionized the way scientists think about the innermost planet. Analyses of new data from the spacecraft show, among other things, new evidence that flood volcanism has been widespread on Mercury, the first close-up views of Mercury's "hollows," the first direct measurements of the chemical composition of Mercury's surface, and the first global inventory of plasma ions within Mercury's space environment.

The results are reported in a set of seven papers published in a special section of Science magazine on Sept. 30, 2011 (available online at: http://www.sciencemag.org/site/feature/data/hottopics/messenger/)

"MESSENGER's instruments are capturing data that can be obtained only from orbit," says MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution of Washington. "We have imaged many areas of the surface at unprecedented resolution, we have viewed the polar regions clearly for the first time, we have built up global coverage with our images and other data sets, we are mapping the elemental composition of Mercury's surface, we are conducting a continuous inventory of the planet's neutral and ionized exosphere, and we are sorting out the geometry of Mercury's magnetic field and magnetosphere. And we've only just begun. Mercury has many more surprises in store for us as our mission progresses."

MESSENGER Reveals Flood Volcanism

For decades scientists had puzzled over whether Mercury had volcanic deposits on its surface. MESSENGER's three flybys answered that question in the affirmative, but the global distribution of volcanic materials was not well constrained. New data from orbit show a huge expanse of volcanic plains surrounding the north polar region of Mercury. These continuous smooth plains cover more than 6% of the total surface of Mercury.

The volcanic deposits are thick. "Analysis of the size of buried 'ghost' craters in these deposits shows that the lavas are locally as thick as 2 kilometers" (or 1.2 miles), explains James Head of Brown University, the lead author of one of the Science reports. "If you imagine standing at the base of the Washington Monument, the top of the lavas would be something like 12 Washington Monuments above you."

According to Head, the deposits appear typical of flood lavas, huge volumes of solidified molten rock similar to those found in the few-million-year-old Columbia River Basalt Group, which at one point covered 150,000 square kilometers (60,000 square miles) in the northwest United States. "Those on Mercury appear to have poured out from long, linear vents and covered the surrounding areas, flooding them to great depths and burying their source vents," Head says.

Scientists have also discovered vents, measuring up to 25 kilometers (16 miles) in length, that appear to be the source of some of the tremendous volumes of very hot lava that have rushed out over the surface of Mercury and eroded the substrate, carving valleys and creating teardrop-shaped ridges in the underlying terrain. "These amazing landforms and deposits may be related to the types of unusual compositions, similar to terrestrial rocks called komatiites, being seen by other instruments and reported in this same issue of Science," Head says. "What's more, such lavas may have been typical of an early period in Earth's history, one for which only spotty evidence remains today."

As MESSENGER continues to orbit Mercury, the imaging team is building up a global catalog of these volcanic deposits and is working with other instrument teams to construct a comprehensive view of the history of volcanism on Mercury.

Hollows on Mercury

Images collected by MESSENGER have revealed an unexpected class of landform on Mercury and suggest that a previously unrecognized geological process is responsible for its formation. Images collected during the Mariner 10 and MESSENGER flybys of Mercury showed that the floors and central mountain peaks of some impact craters are very bright and have a blue color relative to other areas of Mercury. These deposits were considered to be unusual because no craters with similar characteristics are found on the Moon. But without higher-resolution images, the bright crater deposits remained a curiosity.

Now MESSENGER's orbital mission has provided close-up, targeted views of many of these craters.

"To the surprise of the science team, it turns out that the bright areas are composed of small, shallow, irregularly shaped depressions that are often found in clusters," says David Blewett, a staff scientist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., and lead author of one of the Science reports. "The science team adopted the term 'hollows' for these features to distinguish them from other types of pits seen on Mercury."

Hollows have been found over a wide range of latitudes and longitudes, suggesting that they are fairly common across Mercury. Many of the depressions have bright interiors and halos, and Blewett says the ones detected so far have a fresh appearance and have not accumulated small impact craters, indicating that they are relatively young.

"Analysis of the images and estimates of the rate at which the hollows may be growing led to the conclusion that they could be actively forming today," Blewett says. "The old conventional wisdom was that 'Mercury is just like the Moon.' But from its vantage point in orbit, MESSENGER is showing us that Mercury is radically different from the Moon in just about every way we can measure."

Mercury's Surface and Exospheric Composition, Up Close and Personal

Scientists are collecting data about the chemical composition of Mercury's surface that could not have been obtained without the sustained observing perspective that MESSENGER's orbit provides, and that information is being used to test models of Mercury's formation and shed light on the dynamics of the planet's exosphere.

Measurements of Mercury's surface by MESSENGER's Gamma-Ray Spectrometer (GRS) reveal a higher abundance of the radioactive element potassium, a moderately volatile element that vaporizes at a relatively low temperature, than previously predicted. Together with MESSENGER's X-Ray Spectrometer (XRS), it also shows that Mercury has an average surface composition different from those of the Moon and other terrestrial planets.

"Measurements of the ratio of potassium to thorium, another radioactive element, along with the abundance of sulfur detected by XRS, indicate that Mercury has a volatile inventory similar to Venus, Earth, and Mars, and much larger than that of the Moon," says APL Staff Scientist Patrick Peplowski, lead author of one of the Science papers.

These new data rule out most existing models for Mercury's formation that had been developed to explain the unusually high density of the innermost planet, which has a much higher mass fraction of iron metal than Venus, Earth, or Mars, Peplowski pointed out. Overall, Mercury's surface composition is similar to that expected if the planet's bulk composition is broadly similar to that of highly reduced or metal-rich chondritic meteorites (material that is left over from the formation of the solar system).

MESSENGER has also collected the first global observations of plasma ions in Mercury's magnetosphere. Over 65 days covering more than 120 orbits, MESSENGER's Fast Imaging Plasma Spectrometer (FIPS) made the first long-term measurements of Mercury's ionized exosphere.

The team found that sodium is the most important ion contributed by the planet. "We had previously observed neutral sodium from ground observations, but up close we've discovered that charged sodium particles are concentrated near Mercury's polar regions where they are likely liberated by solar wind ion sputtering, effectively knocking sodium atoms off Mercury's surface," notes the University of Michigan's Thomas Zurbuchen, author of one of the Science reports. "We were able to observe the formation process of these ions, one that is comparable to the manner by which auroras are generated in the Earth atmosphere near polar regions."

The FIPS sensor detected helium ions throughout the entire volume of Mercury's magnetosphere. "Helium must be generated through surface interactions with the solar wind," says Zurbuchen. "We surmise that the helium was delivered from the Sun by the solar wind, implanted on the surface of Mercury, and then fanned out in all directions.

"Our results tell us that Mercury's weak magnetosphere provides the planet very little protection from the solar wind," he continued. "Extreme space weather must be a continuing activity at the surface of the planet closest to the Sun."

"These revelations emphasize that Mercury is a fascinating world that is unmatched in the solar system," says Blewett. "We have barely begun to understand what Mercury is really like and are eager to discover what Mercury can tell us about the processes that led to formation of the planets as we see them today."

For more supporting materials, visit: http://messenger.jhuapl.edu/news_room/telecon7.html

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by NASA.

Journal References:

L. R. Nittler, R. D. Starr, S. Z. Weider, T. J. McCoy, W. V. Boynton, D. S. Ebel, C. M. Ernst, L. G. Evans, J. O. Goldsten, D. K. Hamara, D. J. Lawrence, R. L. McNutt, C. E. Schlemm, S. C. Solomon, A. L. Sprague. The Major-Element Composition of Mercury's Surface from MESSENGER X-ray Spectrometry. Science, 2011; 333 (6051): 1847 DOI: 10.1126/science.1211567P. N. Peplowski, L. G. Evans, S. A. Hauck, T. J. McCoy, W. V. Boynton, J. J. Gillis-Davis, D. S. Ebel, J. O. Goldsten, D. K. Hamara, D. J. Lawrence, R. L. McNutt, L. R. Nittler, S. C. Solomon, E. A. Rhodes, A. L. Sprague, R. D. Starr, K. R. Stockstill-Cahill. Radioactive Elements on Mercury's Surface from MESSENGER: Implications for the Planet's Formation and Evolution. Science, 2011; 333 (6051): 1850 DOI: 10.1126/science.1211576J. W. Head, C. R. Chapman, R. G. Strom, C. I. Fassett, B. W. Denevi, D. T. Blewett, C. M. Ernst, T. R. Watters, S. C. Solomon, S. L. Murchie, L. M. Prockter, N. L. Chabot, J. J. Gillis-Davis, J. L. Whitten, T. A. Goudge, D. M. H. Baker, D. M. Hurwitz, L. R. Ostrach, Z. Xiao, W. J. Merline, L. Kerber, J. L. Dickson, J. Oberst, P. K. Byrne, C. Klimczak, L. R. Nittler. Flood Volcanism in the Northern High Latitudes of Mercury Revealed by MESSENGER. Science, 2011; 333 (6051): 1853 DOI: 10.1126/science.1211997D. T. Blewett, N. L. Chabot, B. W. Denevi, C. M. Ernst, J. W. Head, N. R. Izenberg, S. L. Murchie, S. C. Solomon, L. R. Nittler, T. J. McCoy, Z. Xiao, D. M. H. Baker, C. I. Fassett, S. E. Braden, J. Oberst, F. Scholten, F. Preusker, D. M. Hurwitz. Hollows on Mercury: MESSENGER Evidence for Geologically Recent Volatile-Related Activity. Science, 2011; 333 (6051): 1856 DOI: 10.1126/science.1211681B. J. Anderson, C. L. Johnson, H. Korth, M. E. Purucker, R. M. Winslow, J. A. Slavin, S. C. Solomon, R. L. McNutt, J. M. Raines, T. H. Zurbuchen. The Global Magnetic Field of Mercury from MESSENGER Orbital Observations. Science, 2011; 333 (6051): 1859 DOI: 10.1126/science.1211001T. H. Zurbuchen, J. M. Raines, J. A. Slavin, D. J. Gershman, J. A. Gilbert, G. Gloeckler, B. J. Anderson, D. N. Baker, H. Korth, S. M. Krimigis, M. Sarantos, D. Schriver, R. L. McNutt, S. C. Solomon. MESSENGER Observations of the Spatial Distribution of Planetary Ions Near Mercury. Science, 2011; 333 (6051): 1862 DOI: 10.1126/science.1211302G. C. Ho, S. M. Krimigis, R. E. Gold, D. N. Baker, J. A. Slavin, B. J. Anderson, H. Korth, R. D. Starr, D. J. Lawrence, R. L. McNutt, S. C. Solomon. MESSENGER Observations of Transient Bursts of Energetic Electrons in Mercury's Magnetosphere. Science, 2011; 333 (6051): 1865 DOI: 10.1126/science.1211141

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Astronomers reveal supernova factory

ScienceDaily (Oct. 2, 2011) — A team led by astronomers at Chalmers and Onsala Space Observatory has detected seven previously unknown supernovae in a galaxy 250 million light years away. Never before have so many supernovae been discovered at the same time in the same galaxy. The discovery proves what astronomers have long believed: that the galaxies which are the universe's most efficient star-factories are also supernova factories.

The astronomers used a worldwide network of radio telescopes in five countries, including Sweden, to be able to create extremely sharp images of the galaxy Arp 220. The scientists observed around 40 radio sources in the center of the galaxy Arp 220. These radio sources are hidden behind thick layers of dust and gas and invisible in ordinary telescopes. To discover the nature of these radio sources, they made measurements at different radio wavelengths and watched how they changed over several years.

"With all the data in place, we can now be certain that all seven of these sources are supernovae: stars that exploded in the last 60 years," says Fabien Batejat, main author of the article about the discovery.

So many supernovae have never before been detected in the same galaxy. The number is nevertheless consistent with how fast stars are forming in Arp 220.

"In Arp 220, we see far more supernovae than in our galaxy. We estimate that a star explodes in Arp 220 once every quarter. In the Milky Way, there is only one supernova per century," says Rodrigo Parra, astronomer at the European Southern Observatory in Chile and member of the team.

John Conway is professor of observational radio astronomy at Chalmers and deputy director of Onsala Space Observatory.

"Arp 220 is well-known as a place where star formation is very efficient. Now we have been able to show that star factories like this are also supernova factories," he says.

The radio measurements have also given researchers insight into how radio waves are generated in supernovae and their remnants.

"Our measurements show that a supernova's own magnetic field is what gives rise to its radio emission, not the magnetic fields in the galaxy around it," says Fabien Batejat.

The results will be published in the October 20 issue of the journal Astrophysical Journal.

The team is composed of Fabien Batejat, John Conway and Rossa Hurley from Onsala Space Observatory at Chalmers, Rodrigo Parra (European Southern Observatory, ESO, Santiago, Chile), Philip Diamond (CSIRO, Sydney, Australia), Colin J. Lonsdale (MIT Haystack Observatory, USA) and Carol J. Lonsdale (North American Alma Science Center, NRAO, Charlottesville, USA).

The observations were carried out using telescopes which belong to the European VLBI Network (EVN) together with the Very Long Baseline Array (VLBA). The VLBA is a set of ten radio telescopes located from Hawaii to St. Croix in the U.S. Virgin Islands and operated by the National Radio Astronomy Observatory.

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Chalmers University of Technology.

Journal Reference:

Fabien Batejat, John E. Conway, Rossa Hurley, Rodrigo Parra, Philip J. Diamond, Colin J. Lonsdale, Carol J. Lonsdale. Resolution of the Compact Radio Continuum Sources in Arp220. Astrophysical Journal, 2011; (in press) [link]

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Space telescopes reveal secrets of turbulent black hole

ScienceDaily (Sep. 30, 2011) — Supermassive black holes at the hearts of active galaxies swallow large amounts of gas. During this feast they spill a lot of their 'food', which is discharged in turbulent outbursts. An international team of astronomers has revealed some striking features of such an outburst around a supermassive black hole in a distant galaxy. They found a very hot 'convertor' corona hovering above the black hole and cold gas 'bullets' in hotter diffuse gas, speeding outwards with velocities up to 700 km/s.

Unlike popular belief, not all the matter around a black hole is swallowed up. A disc of infalling gas forms around the black hole. On the journey inwards the gas and dust emit large amounts of X-ray and UV radiation. This radiation can be so strong that it diverts a part of the gas inflow. It causes winds flowing outward with velocities up to several hundreds of km/s. An international team of astronomers led by Dr. Jelle Kaastra from the SRON Netherlands Institute for Space Research took the opportunity to observe and map such an extreme environment around one of the brightest supermassive black holes known to us. This 'monster' black hole -- in the distant galaxy Markarian 509 -- has a mass 300 million times that of the Sun.

Convertor corona

The Markarian 509 black hole is surrounded by a disc of gas shining bright in ultraviolet light. This emission varies in a synchronised way with emissions observed at the low end of the X-ray band, some 100s of times higher in energy than visible light. "The only way to explain this is by having gas hotter than that in the disc, a so-called 'corona', hovering above the disc," Jelle Kaastra says. "This corona absorbs and reprocesses the ultraviolet light from the disc, energising it and converting it into X-ray light. It must have a temperature of a few million degrees. Using five space telescopes, which enabled us to observe the area in unprecedented detail, we actually discovered a very hot 'corona' of gas hovering above the disc. This discovery allows us to make sense of some of the observations of active galaxies that have been hard to explain so far."

Cold gas bullets

The X-ray spectrum obtained with the Reflection Grating Spectrometer (RGS) of the space telescope XMM-Newton is the best obtained so far of such a system. It reveals unprecedented details of its gaseous environment. For the first time it has been possible to show that the outflow consists of at least five distinct components with temperatures ranging between 20.000 to a million degrees. The superb ultraviolet spectrum obtained by the Cosmic Origins Spectrograph of the Hubble Space Telescope reveals that the coolest gas in the line of sight towards Markarian 509 has 14 different velocity components at various locations in the innermost parts of this galaxy. Thus far only seven velocity components were identified.

The combined X-ray and UV measurements demonstrate that most of the visible outflowing gas is blown off from a dusty gas torus surrounding the central region more than 15 light years away from the black hole. This outflow consists of dense, cold blobs or gas bullets embedded in hotter diffuse gas. "Even at a distance of 15 light years, the energy released near the black hole manages to blow off gas from the dusty torus that surrounds the disc of infalling gas," Kaastra says.

Signs of cosmic collision

Further outwards, the signatures of the interstellar gas of the host galaxy are seen. That gas is strongly ionised by the central X-ray source: atoms are stripped of some or most of their electrons when illuminated by the powerful flux of X-rays. Even further out, at hundred thousands of light years, the X-ray light shines through gas falling in towards Markarian 509 with speeds of 200 km/s. This gas may point at a collision with a smaller galaxy in the past, that may have triggered the activity of Markarian 509.

Space telescopes

Five large space telescopes were involved in this hundred days campaign that took place in late 2009. The heart of the campaign consisted of repeated visible, X-ray and gamma-ray observations with ESA's XMM-Newton and INTEGRAL satellites, which monitored Markarian 509 for six weeks. This was followed by long observations with NASA's Chandra X-ray satellite, using the Low Energy Transmission Grating, and the NASA/ESA Hubble Space Telescope using the new Cosmic Origins Spectrograph. Prior to these observations short snapshots to monitor the behaviour of the source at all wavelengths were taken with the Swift satellite.

The combined efforts of all these instruments and astronomers gave an unprecedented insight into the core of an active galaxy. Right in the middle of the campaign the source went into outburst. The physical changes due to this outburst could be followed over the electromagnetic spectrum from visible light to X-rays.

Papers

The international consortium responsible for this campaign consists of 26 astronomers from 21 institutes on 4 continents. The first results of this campaign will be published as a series of 7 papers in Astronomy and Astrophysics, titled Multiwavelength campaign on Mrk 509 (see below). More results are in preparation.

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by SRON Netherlands Institute for Space Research.

Journal References:

J. S. Kaastra, P.-O. Petrucci, M. Cappi, N. Arav, E. Behar, S. Bianchi, J. Bloom, A. J. Blustin, G. Branduardi-Raymont, E. Costantini, M. Dadina, R. G. Detmers, J. Ebrero, P. G. Jonker, C. Klein, G. A. Kriss, P. Lubinski, J. Malzac, M. Mehdipour, S. Paltani, C. Pinto, G. Ponti, E. M. Ratti, R. A. N. Smith, K. C. Steenbrugge, C. P. de Vries. Multiwavelength campaign on Mrk 509: I. Variability and spectral energy distribution. Astronomy & Astrophysics, 2011; 534: A36 DOI: 10.1051/0004-6361/201116869J. S. Kaastra, C. P. de Vries, K. C. Steenbrugge, R. G. Detmers, J. Ebrero, E. Behar, S. Bianchi, E. Costantini, G. A. Kriss, M. Mehdipour, S. Paltani, P.-O. Petrucci, C. Pinto, G. Ponti. Multiwavelength campaign on Mrk 509: II. Analysis of high-quality Reflection Grating Spectrometer spectra. Astronomy & Astrophysics, 2011; 534: A37 DOI: 10.1051/0004-6361/201116870R. G. Detmers, J. S. Kaastra, K. C. Steenbrugge, J. Ebrero, G. A. Kriss, N. Arav, E. Behar, E. Costantini, G. Branduardi-Raymont, M. Mehdipour, S. Bianchi, M. Cappi, P. Petrucci, G. Ponti, C. Pinto, E. M. Ratti, T. Holczer. Multiwavelength campaign on Mrk 509: III. The 600 ks RGS spectrum: unravelling the inner region of an AGN. Astronomy & Astrophysics, 2011; 534: A38 DOI: 10.1051/0004-6361/201116899M. Mehdipour, G. Branduardi-Raymont, J. S. Kaastra, P. O. Petrucci, G. A. Kriss, G. Ponti, A. J. Blustin, S. Paltani, M. Cappi, R. G. Detmers, K. C. Steenbrugge. Multiwavelength campaign on Mrk 509: IV. Optical-UV-X-ray variability and the nature of the soft X-ray excess. Astronomy & Astrophysics, 2011; 534: A39 DOI: 10.1051/0004-6361/201116875J. Ebrero, G. A. Kriss, J. S. Kaastra, R. G. Detmers, K. C. Steenbrugge, E. Costantini, N. Arav, S. Bianchi, M. Cappi, G. Branduardi-Raymont, M. Mehdipour, P. O. Petrucci, C. Pinto, G. Ponti. Multiwavelength campaign on Mrk 509: V. Chandra-LETGS observation of the ionized absorber. Astronomy & Astrophysics, 2011; 534: A40 DOI: 10.1051/0004-6361/201117067G. A. Kriss, N. Arav, J. S. Kaastra, J. Ebrero, C. Pinto, B. Borguet, D. Edmonds, E. Costantini, K. C. Steenbrugge, R. G. Detmers, E. Behar, S. Bianchi, A. J. Blustin, G. Branduardi-Raymont, M. Cappi, M. Mehdipour, P. Petrucci, G. Ponti. Multiwavelength campaign on Mrk 509: VI. HST/COS observations of the far-ultraviolet spectrum. Astronomy & Astrophysics, 2011; 534: A41 DOI: 10.1051/0004-6361/201117123K. C. Steenbrugge, J. S. Kaastra, R. G. Detmers, J. Ebrero, G. Ponti, E. Costantini, G. A. Kriss, M. Mehdipour, C. Pinto, G. Branduardi-Raymont, E. Behar, N. Arav, M. Cappi, S. Bianchi, P.-O. Petrucci, E. M. Ratti, T. Holczer. Multiwavelength campaign on Mrk 509: VII. Relative abundances of the warm absorber. Astronomy & Astrophysics, 2011; 534: A42 DOI: 10.1051/0004-6361/201117304

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Astronomers reveal supernova factory

ScienceDaily (Oct. 2, 2011) — A team led by astronomers at Chalmers and Onsala Space Observatory has detected seven previously unknown supernovae in a galaxy 250 million light years away. Never before have so many supernovae been discovered at the same time in the same galaxy. The discovery proves what astronomers have long believed: that the galaxies which are the universe's most efficient star-factories are also supernova factories.

The astronomers used a worldwide network of radio telescopes in five countries, including Sweden, to be able to create extremely sharp images of the galaxy Arp 220. The scientists observed around 40 radio sources in the center of the galaxy Arp 220. These radio sources are hidden behind thick layers of dust and gas and invisible in ordinary telescopes. To discover the nature of these radio sources, they made measurements at different radio wavelengths and watched how they changed over several years.

"With all the data in place, we can now be certain that all seven of these sources are supernovae: stars that exploded in the last 60 years," says Fabien Batejat, main author of the article about the discovery.

So many supernovae have never before been detected in the same galaxy. The number is nevertheless consistent with how fast stars are forming in Arp 220.

"In Arp 220, we see far more supernovae than in our galaxy. We estimate that a star explodes in Arp 220 once every quarter. In the Milky Way, there is only one supernova per century," says Rodrigo Parra, astronomer at the European Southern Observatory in Chile and member of the team.

John Conway is professor of observational radio astronomy at Chalmers and deputy director of Onsala Space Observatory.

"Arp 220 is well-known as a place where star formation is very efficient. Now we have been able to show that star factories like this are also supernova factories," he says.

The radio measurements have also given researchers insight into how radio waves are generated in supernovae and their remnants.

"Our measurements show that a supernova's own magnetic field is what gives rise to its radio emission, not the magnetic fields in the galaxy around it," says Fabien Batejat.

The results will be published in the October 20 issue of the journal Astrophysical Journal.

The team is composed of Fabien Batejat, John Conway and Rossa Hurley from Onsala Space Observatory at Chalmers, Rodrigo Parra (European Southern Observatory, ESO, Santiago, Chile), Philip Diamond (CSIRO, Sydney, Australia), Colin J. Lonsdale (MIT Haystack Observatory, USA) and Carol J. Lonsdale (North American Alma Science Center, NRAO, Charlottesville, USA).

The observations were carried out using telescopes which belong to the European VLBI Network (EVN) together with the Very Long Baseline Array (VLBA). The VLBA is a set of ten radio telescopes located from Hawaii to St. Croix in the U.S. Virgin Islands and operated by the National Radio Astronomy Observatory.

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Chalmers University of Technology.

Journal Reference:

Fabien Batejat, John E. Conway, Rossa Hurley, Rodrigo Parra, Philip J. Diamond, Colin J. Lonsdale, Carol J. Lonsdale. Resolution of the Compact Radio Continuum Sources in Arp220. Astrophysical Journal, 2011; (in press) [link]

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Space telescopes reveal secrets of turbulent black hole

ScienceDaily (Sep. 30, 2011) — Supermassive black holes at the hearts of active galaxies swallow large amounts of gas. During this feast they spill a lot of their 'food', which is discharged in turbulent outbursts. An international team of astronomers has revealed some striking features of such an outburst around a supermassive black hole in a distant galaxy. They found a very hot 'convertor' corona hovering above the black hole and cold gas 'bullets' in hotter diffuse gas, speeding outwards with velocities up to 700 km/s.

Unlike popular belief, not all the matter around a black hole is swallowed up. A disc of infalling gas forms around the black hole. On the journey inwards the gas and dust emit large amounts of X-ray and UV radiation. This radiation can be so strong that it diverts a part of the gas inflow. It causes winds flowing outward with velocities up to several hundreds of km/s. An international team of astronomers led by Dr. Jelle Kaastra from the SRON Netherlands Institute for Space Research took the opportunity to observe and map such an extreme environment around one of the brightest supermassive black holes known to us. This 'monster' black hole -- in the distant galaxy Markarian 509 -- has a mass 300 million times that of the Sun.

Convertor corona

The Markarian 509 black hole is surrounded by a disc of gas shining bright in ultraviolet light. This emission varies in a synchronised way with emissions observed at the low end of the X-ray band, some 100s of times higher in energy than visible light. "The only way to explain this is by having gas hotter than that in the disc, a so-called 'corona', hovering above the disc," Jelle Kaastra says. "This corona absorbs and reprocesses the ultraviolet light from the disc, energising it and converting it into X-ray light. It must have a temperature of a few million degrees. Using five space telescopes, which enabled us to observe the area in unprecedented detail, we actually discovered a very hot 'corona' of gas hovering above the disc. This discovery allows us to make sense of some of the observations of active galaxies that have been hard to explain so far."

Cold gas bullets

The X-ray spectrum obtained with the Reflection Grating Spectrometer (RGS) of the space telescope XMM-Newton is the best obtained so far of such a system. It reveals unprecedented details of its gaseous environment. For the first time it has been possible to show that the outflow consists of at least five distinct components with temperatures ranging between 20.000 to a million degrees. The superb ultraviolet spectrum obtained by the Cosmic Origins Spectrograph of the Hubble Space Telescope reveals that the coolest gas in the line of sight towards Markarian 509 has 14 different velocity components at various locations in the innermost parts of this galaxy. Thus far only seven velocity components were identified.

The combined X-ray and UV measurements demonstrate that most of the visible outflowing gas is blown off from a dusty gas torus surrounding the central region more than 15 light years away from the black hole. This outflow consists of dense, cold blobs or gas bullets embedded in hotter diffuse gas. "Even at a distance of 15 light years, the energy released near the black hole manages to blow off gas from the dusty torus that surrounds the disc of infalling gas," Kaastra says.

Signs of cosmic collision

Further outwards, the signatures of the interstellar gas of the host galaxy are seen. That gas is strongly ionised by the central X-ray source: atoms are stripped of some or most of their electrons when illuminated by the powerful flux of X-rays. Even further out, at hundred thousands of light years, the X-ray light shines through gas falling in towards Markarian 509 with speeds of 200 km/s. This gas may point at a collision with a smaller galaxy in the past, that may have triggered the activity of Markarian 509.

Space telescopes

Five large space telescopes were involved in this hundred days campaign that took place in late 2009. The heart of the campaign consisted of repeated visible, X-ray and gamma-ray observations with ESA's XMM-Newton and INTEGRAL satellites, which monitored Markarian 509 for six weeks. This was followed by long observations with NASA's Chandra X-ray satellite, using the Low Energy Transmission Grating, and the NASA/ESA Hubble Space Telescope using the new Cosmic Origins Spectrograph. Prior to these observations short snapshots to monitor the behaviour of the source at all wavelengths were taken with the Swift satellite.

The combined efforts of all these instruments and astronomers gave an unprecedented insight into the core of an active galaxy. Right in the middle of the campaign the source went into outburst. The physical changes due to this outburst could be followed over the electromagnetic spectrum from visible light to X-rays.

Papers

The international consortium responsible for this campaign consists of 26 astronomers from 21 institutes on 4 continents. The first results of this campaign will be published as a series of 7 papers in Astronomy and Astrophysics, titled Multiwavelength campaign on Mrk 509 (see below). More results are in preparation.

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by SRON Netherlands Institute for Space Research.

Journal References:

J. S. Kaastra, P.-O. Petrucci, M. Cappi, N. Arav, E. Behar, S. Bianchi, J. Bloom, A. J. Blustin, G. Branduardi-Raymont, E. Costantini, M. Dadina, R. G. Detmers, J. Ebrero, P. G. Jonker, C. Klein, G. A. Kriss, P. Lubinski, J. Malzac, M. Mehdipour, S. Paltani, C. Pinto, G. Ponti, E. M. Ratti, R. A. N. Smith, K. C. Steenbrugge, C. P. de Vries. Multiwavelength campaign on Mrk 509: I. Variability and spectral energy distribution. Astronomy & Astrophysics, 2011; 534: A36 DOI: 10.1051/0004-6361/201116869J. S. Kaastra, C. P. de Vries, K. C. Steenbrugge, R. G. Detmers, J. Ebrero, E. Behar, S. Bianchi, E. Costantini, G. A. Kriss, M. Mehdipour, S. Paltani, P.-O. Petrucci, C. Pinto, G. Ponti. Multiwavelength campaign on Mrk 509: II. Analysis of high-quality Reflection Grating Spectrometer spectra. Astronomy & Astrophysics, 2011; 534: A37 DOI: 10.1051/0004-6361/201116870R. G. Detmers, J. S. Kaastra, K. C. Steenbrugge, J. Ebrero, G. A. Kriss, N. Arav, E. Behar, E. Costantini, G. Branduardi-Raymont, M. Mehdipour, S. Bianchi, M. Cappi, P. Petrucci, G. Ponti, C. Pinto, E. M. Ratti, T. Holczer. Multiwavelength campaign on Mrk 509: III. The 600 ks RGS spectrum: unravelling the inner region of an AGN. Astronomy & Astrophysics, 2011; 534: A38 DOI: 10.1051/0004-6361/201116899M. Mehdipour, G. Branduardi-Raymont, J. S. Kaastra, P. O. Petrucci, G. A. Kriss, G. Ponti, A. J. Blustin, S. Paltani, M. Cappi, R. G. Detmers, K. C. Steenbrugge. Multiwavelength campaign on Mrk 509: IV. Optical-UV-X-ray variability and the nature of the soft X-ray excess. Astronomy & Astrophysics, 2011; 534: A39 DOI: 10.1051/0004-6361/201116875J. Ebrero, G. A. Kriss, J. S. Kaastra, R. G. Detmers, K. C. Steenbrugge, E. Costantini, N. Arav, S. Bianchi, M. Cappi, G. Branduardi-Raymont, M. Mehdipour, P. O. Petrucci, C. Pinto, G. Ponti. Multiwavelength campaign on Mrk 509: V. Chandra-LETGS observation of the ionized absorber. Astronomy & Astrophysics, 2011; 534: A40 DOI: 10.1051/0004-6361/201117067G. A. Kriss, N. Arav, J. S. Kaastra, J. Ebrero, C. Pinto, B. Borguet, D. Edmonds, E. Costantini, K. C. Steenbrugge, R. G. Detmers, E. Behar, S. Bianchi, A. J. Blustin, G. Branduardi-Raymont, M. Cappi, M. Mehdipour, P. Petrucci, G. Ponti. Multiwavelength campaign on Mrk 509: VI. HST/COS observations of the far-ultraviolet spectrum. Astronomy & Astrophysics, 2011; 534: A41 DOI: 10.1051/0004-6361/201117123K. C. Steenbrugge, J. S. Kaastra, R. G. Detmers, J. Ebrero, G. Ponti, E. Costantini, G. A. Kriss, M. Mehdipour, C. Pinto, G. Branduardi-Raymont, E. Behar, N. Arav, M. Cappi, S. Bianchi, P.-O. Petrucci, E. M. Ratti, T. Holczer. Multiwavelength campaign on Mrk 509: VII. Relative abundances of the warm absorber. Astronomy & Astrophysics, 2011; 534: A42 DOI: 10.1051/0004-6361/201117304

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Orbital observations of Mercury reveal flood lavas, hollows, and unprecedented surface details

ScienceDaily (Sep. 29, 2011) — After only six months in orbit around Mercury, NASA's MESSENGER spacecraft is sending back information that has revolutionized the way scientists think about the innermost planet. Analyses of new data from the spacecraft show, among other things, new evidence that flood volcanism has been widespread on Mercury, the first close-up views of Mercury's "hollows," the first direct measurements of the chemical composition of Mercury's surface, and the first global inventory of plasma ions within Mercury's space environment.

The results are reported in a set of seven papers published in a special section of Science magazine on Sept. 30, 2011 (available online at: http://www.sciencemag.org/site/feature/data/hottopics/messenger/)

"MESSENGER's instruments are capturing data that can be obtained only from orbit," says MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution of Washington. "We have imaged many areas of the surface at unprecedented resolution, we have viewed the polar regions clearly for the first time, we have built up global coverage with our images and other data sets, we are mapping the elemental composition of Mercury's surface, we are conducting a continuous inventory of the planet's neutral and ionized exosphere, and we are sorting out the geometry of Mercury's magnetic field and magnetosphere. And we've only just begun. Mercury has many more surprises in store for us as our mission progresses."

MESSENGER Reveals Flood Volcanism

For decades scientists had puzzled over whether Mercury had volcanic deposits on its surface. MESSENGER's three flybys answered that question in the affirmative, but the global distribution of volcanic materials was not well constrained. New data from orbit show a huge expanse of volcanic plains surrounding the north polar region of Mercury. These continuous smooth plains cover more than 6% of the total surface of Mercury.

The volcanic deposits are thick. "Analysis of the size of buried 'ghost' craters in these deposits shows that the lavas are locally as thick as 2 kilometers" (or 1.2 miles), explains James Head of Brown University, the lead author of one of the Science reports. "If you imagine standing at the base of the Washington Monument, the top of the lavas would be something like 12 Washington Monuments above you."

According to Head, the deposits appear typical of flood lavas, huge volumes of solidified molten rock similar to those found in the few-million-year-old Columbia River Basalt Group, which at one point covered 150,000 square kilometers (60,000 square miles) in the northwest United States. "Those on Mercury appear to have poured out from long, linear vents and covered the surrounding areas, flooding them to great depths and burying their source vents," Head says.

Scientists have also discovered vents, measuring up to 25 kilometers (16 miles) in length, that appear to be the source of some of the tremendous volumes of very hot lava that have rushed out over the surface of Mercury and eroded the substrate, carving valleys and creating teardrop-shaped ridges in the underlying terrain. "These amazing landforms and deposits may be related to the types of unusual compositions, similar to terrestrial rocks called komatiites, being seen by other instruments and reported in this same issue of Science," Head says. "What's more, such lavas may have been typical of an early period in Earth's history, one for which only spotty evidence remains today."

As MESSENGER continues to orbit Mercury, the imaging team is building up a global catalog of these volcanic deposits and is working with other instrument teams to construct a comprehensive view of the history of volcanism on Mercury.

Hollows on Mercury

Images collected by MESSENGER have revealed an unexpected class of landform on Mercury and suggest that a previously unrecognized geological process is responsible for its formation. Images collected during the Mariner 10 and MESSENGER flybys of Mercury showed that the floors and central mountain peaks of some impact craters are very bright and have a blue color relative to other areas of Mercury. These deposits were considered to be unusual because no craters with similar characteristics are found on the Moon. But without higher-resolution images, the bright crater deposits remained a curiosity.

Now MESSENGER's orbital mission has provided close-up, targeted views of many of these craters.

"To the surprise of the science team, it turns out that the bright areas are composed of small, shallow, irregularly shaped depressions that are often found in clusters," says David Blewett, a staff scientist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., and lead author of one of the Science reports. "The science team adopted the term 'hollows' for these features to distinguish them from other types of pits seen on Mercury."

Hollows have been found over a wide range of latitudes and longitudes, suggesting that they are fairly common across Mercury. Many of the depressions have bright interiors and halos, and Blewett says the ones detected so far have a fresh appearance and have not accumulated small impact craters, indicating that they are relatively young.

"Analysis of the images and estimates of the rate at which the hollows may be growing led to the conclusion that they could be actively forming today," Blewett says. "The old conventional wisdom was that 'Mercury is just like the Moon.' But from its vantage point in orbit, MESSENGER is showing us that Mercury is radically different from the Moon in just about every way we can measure."

Mercury's Surface and Exospheric Composition, Up Close and Personal

Scientists are collecting data about the chemical composition of Mercury's surface that could not have been obtained without the sustained observing perspective that MESSENGER's orbit provides, and that information is being used to test models of Mercury's formation and shed light on the dynamics of the planet's exosphere.

Measurements of Mercury's surface by MESSENGER's Gamma-Ray Spectrometer (GRS) reveal a higher abundance of the radioactive element potassium, a moderately volatile element that vaporizes at a relatively low temperature, than previously predicted. Together with MESSENGER's X-Ray Spectrometer (XRS), it also shows that Mercury has an average surface composition different from those of the Moon and other terrestrial planets.

"Measurements of the ratio of potassium to thorium, another radioactive element, along with the abundance of sulfur detected by XRS, indicate that Mercury has a volatile inventory similar to Venus, Earth, and Mars, and much larger than that of the Moon," says APL Staff Scientist Patrick Peplowski, lead author of one of the Science papers.

These new data rule out most existing models for Mercury's formation that had been developed to explain the unusually high density of the innermost planet, which has a much higher mass fraction of iron metal than Venus, Earth, or Mars, Peplowski pointed out. Overall, Mercury's surface composition is similar to that expected if the planet's bulk composition is broadly similar to that of highly reduced or metal-rich chondritic meteorites (material that is left over from the formation of the solar system).

MESSENGER has also collected the first global observations of plasma ions in Mercury's magnetosphere. Over 65 days covering more than 120 orbits, MESSENGER's Fast Imaging Plasma Spectrometer (FIPS) made the first long-term measurements of Mercury's ionized exosphere.

The team found that sodium is the most important ion contributed by the planet. "We had previously observed neutral sodium from ground observations, but up close we've discovered that charged sodium particles are concentrated near Mercury's polar regions where they are likely liberated by solar wind ion sputtering, effectively knocking sodium atoms off Mercury's surface," notes the University of Michigan's Thomas Zurbuchen, author of one of the Science reports. "We were able to observe the formation process of these ions, one that is comparable to the manner by which auroras are generated in the Earth atmosphere near polar regions."

The FIPS sensor detected helium ions throughout the entire volume of Mercury's magnetosphere. "Helium must be generated through surface interactions with the solar wind," says Zurbuchen. "We surmise that the helium was delivered from the Sun by the solar wind, implanted on the surface of Mercury, and then fanned out in all directions.

"Our results tell us that Mercury's weak magnetosphere provides the planet very little protection from the solar wind," he continued. "Extreme space weather must be a continuing activity at the surface of the planet closest to the Sun."

"These revelations emphasize that Mercury is a fascinating world that is unmatched in the solar system," says Blewett. "We have barely begun to understand what Mercury is really like and are eager to discover what Mercury can tell us about the processes that led to formation of the planets as we see them today."

For more supporting materials, visit: http://messenger.jhuapl.edu/news_room/telecon7.html

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by NASA.

Journal References:

L. R. Nittler, R. D. Starr, S. Z. Weider, T. J. McCoy, W. V. Boynton, D. S. Ebel, C. M. Ernst, L. G. Evans, J. O. Goldsten, D. K. Hamara, D. J. Lawrence, R. L. McNutt, C. E. Schlemm, S. C. Solomon, A. L. Sprague. The Major-Element Composition of Mercury's Surface from MESSENGER X-ray Spectrometry. Science, 2011; 333 (6051): 1847 DOI: 10.1126/science.1211567P. N. Peplowski, L. G. Evans, S. A. Hauck, T. J. McCoy, W. V. Boynton, J. J. Gillis-Davis, D. S. Ebel, J. O. Goldsten, D. K. Hamara, D. J. Lawrence, R. L. McNutt, L. R. Nittler, S. C. Solomon, E. A. Rhodes, A. L. Sprague, R. D. Starr, K. R. Stockstill-Cahill. Radioactive Elements on Mercury's Surface from MESSENGER: Implications for the Planet's Formation and Evolution. Science, 2011; 333 (6051): 1850 DOI: 10.1126/science.1211576J. W. Head, C. R. Chapman, R. G. Strom, C. I. Fassett, B. W. Denevi, D. T. Blewett, C. M. Ernst, T. R. Watters, S. C. Solomon, S. L. Murchie, L. M. Prockter, N. L. Chabot, J. J. Gillis-Davis, J. L. Whitten, T. A. Goudge, D. M. H. Baker, D. M. Hurwitz, L. R. Ostrach, Z. Xiao, W. J. Merline, L. Kerber, J. L. Dickson, J. Oberst, P. K. Byrne, C. Klimczak, L. R. Nittler. Flood Volcanism in the Northern High Latitudes of Mercury Revealed by MESSENGER. Science, 2011; 333 (6051): 1853 DOI: 10.1126/science.1211997D. T. Blewett, N. L. Chabot, B. W. Denevi, C. M. Ernst, J. W. Head, N. R. Izenberg, S. L. Murchie, S. C. Solomon, L. R. Nittler, T. J. McCoy, Z. Xiao, D. M. H. Baker, C. I. Fassett, S. E. Braden, J. Oberst, F. Scholten, F. Preusker, D. M. Hurwitz. Hollows on Mercury: MESSENGER Evidence for Geologically Recent Volatile-Related Activity. Science, 2011; 333 (6051): 1856 DOI: 10.1126/science.1211681B. J. Anderson, C. L. Johnson, H. Korth, M. E. Purucker, R. M. Winslow, J. A. Slavin, S. C. Solomon, R. L. McNutt, J. M. Raines, T. H. Zurbuchen. The Global Magnetic Field of Mercury from MESSENGER Orbital Observations. Science, 2011; 333 (6051): 1859 DOI: 10.1126/science.1211001T. H. Zurbuchen, J. M. Raines, J. A. Slavin, D. J. Gershman, J. A. Gilbert, G. Gloeckler, B. J. Anderson, D. N. Baker, H. Korth, S. M. Krimigis, M. Sarantos, D. Schriver, R. L. McNutt, S. C. Solomon. MESSENGER Observations of the Spatial Distribution of Planetary Ions Near Mercury. Science, 2011; 333 (6051): 1862 DOI: 10.1126/science.1211302G. C. Ho, S. M. Krimigis, R. E. Gold, D. N. Baker, J. A. Slavin, B. J. Anderson, H. Korth, R. D. Starr, D. J. Lawrence, R. L. McNutt, S. C. Solomon. MESSENGER Observations of Transient Bursts of Energetic Electrons in Mercury's Magnetosphere. Science, 2011; 333 (6051): 1865 DOI: 10.1126/science.1211141

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Astronomers reveal a cosmic 'axis of evil'

ScienceDaily (June 30, 2011) — Astronomers are puzzled by the announcement that the masses of the largest objects in the universe appear to depend on which method is used to weigh them. The new work was presented at a specialist discussion meeting on 'Scaling Relations of Galaxy Clusters' organised by the Astrophysics Research Institute (ARI) at Liverpool John Moores University and supported by the Royal Astronomical Society.

Clusters of galaxies are the largest gravitationally bound objects in the universe containing thousands of galaxies like the Milky Way and their weight is an important probe of their dark matter content and evolution through cosmic time. Measurements used to weigh these systems carried out in three different regions of the electromagnetic spectrum: X-ray, optical and millimetre wavelengths, give rise to significantly different results.

Eduardo Rozo, from the University of Chicago, explained that any two of the measurements can be made to fit easily enough but that always leaves the estimate using the third technique out of line. Dubbed the 'Axis of Evil', it is as if the universe is being difficult by keeping back one or two pieces of the jigsaw and so deliberately preventing us from calibrating our weighing scales properly.

More than 40 of the leading cluster astronomers from UK, Europe and the US attended the meeting to discuss the early results from the Planck satellite, currently scanning the heavens at millimetre wavelengths, looking for the smallest signals from clusters of galaxies and the cosmic background radiation in order to understand the birth of the universe. The Planck measurements were compared with optical images of clusters from the Sloan Digitised Sky Survey and new X-ray observations from the XMM-Newton satellite.

ARI astronomers are taking a leading role in this research through participation in the X-ray cluster work and observations of the constituent galaxies using the largest ground-based optical telescopes.

One possible resolution to the 'Axis of Evil' problem discussed at the meeting is a new population of clusters which is optically bright but also X-ray faint. Dr Jim Bartlett (Univ. Paris), who is one of the astronomers who presented the Planck results, argued that the prospect of a new cluster population which responds differently was a 'frightening prospect' because it overturns age old ideas about the gravitational physics being the same from cluster to cluster.

Chris Collins, LJMU Professor of Cosmology, who organised the meeting said: 'I saw this meeting as an opportunity to bring together experts who study clusters at only one wavelength and don't always talk to their colleagues working at other wavelengths. The results presented are unexpected and all three communities (optical, X-ray and millimetre) will need to work together in the future to figure out what is going on.'

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Royal Astronomical Society (RAS).

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Neutrons, simulations reveal details of molecule that complicates next-generation biofuels

ScienceDaily (June 16, 2011) — A first-of-its-kind combination of experiment and simulation at the Department of Energy's Oak Ridge National Laboratory is providing a close-up look at the molecule that complicates next-generation biofuels.

Lignin, a major component of plant cell walls, aggregates to form clumps, which cause problems during the production of cellulosic ethanol. The exact shape and structure of the aggregates, however, have remained largely unknown.

A team led by ORNL's Jeremy Smith revealed the surface structure of lignin aggregates down to 1 angstrom -- the equivalent of a 10 billionth of a meter or smaller than the width of a carbon atom. The team's findings were published in Physical Review E.

"We've combined neutron scattering experiments with large-scale simulations on ORNL's main supercomputer to reveal that pretreated softwood lignin aggregates are characterized by a highly folded surface," said Smith, who directs ORNL's Center for Molecular Biophysics and holds a Governor's Chair at University of Tennessee.

Lignin clumps can inhibit the conversion of biofuel feedstocks -- for example, switchgrass -- into ethanol, a renewable substitute for gasoline. When enzymes are used to release plant sugars necessary for ethanol production, the lignin aggregates bind to the enzymes and reduce the efficiency of the conversion.

Lignin's highly folded surface creates more opportunities to capture the passing enzymes than a smooth surface would. An improved understanding of the lignin aggregates will aid scientists in efforts to design a more effective pretreatment process, which in turn could lower the cost of biofuels.

"Nature has evolved a very sophisticated mechanism to protect plants against enzymatic attack," said ORNL team member Loukas Petridis. "We're trying to understand the physical basis of biomass recalcitrance -- resistance of the plants to enzymatic degradation."

The complementary techniques of simulation on ORNL's Jaguar supercomputer and neutron scattering at the lab's High Flux Isotope Reactor enabled Smith's team to resolve lignin's structure at scales ranging from 1 to 1,000 angstroms. Smith's project is the first to combine the two methods in biofuel research. "This work illustrates how state-of-the-art neutron scattering and high-performance supercomputing can be integrated to reveal structures of importance to the energy biosciences," Smith said.

The research was supported by DOE's Office of Science and used the resources of the Leadership Computing Facility at ORNL under a DOE INCITE award. Team members include ORNL's Sai Venkatesh Pingali, Volker Urban, William Heller, Hugh O'Neill and Marcus Foston and Arthur Ragauskas from Georgia Institute of Technology.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Oak Ridge National Laboratory.

Journal Reference:

Loukas Petridis, Sai Pingali, Volker Urban, William Heller, Hugh O’Neil, Marcus Foston, Arthur Ragauskas, Jeremy Smith. Self-similar multiscale structure of lignin revealed by neutron scattering and molecular dynamics simulation. Physical Review E, 2011; 83 (6) DOI: 10.1103/PhysRevE.83.061911

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here