Feuding helium dwarf stars exposed by eclipse

ScienceDaily (May 24, 2011) — Researchers at the University of Warwick have found a unique feuding double white dwarf star system where each star appears to have been stripped down to just its helium.

Astronomers know of just over 50 close double white dwarfs, but this was only the second ever eclipsing close white dwarf pair to be found. The University of Warwick astronomers Steven Parsons and Professor Tom Marsh were able to use the fact that the stars eclipse each other when seen from Earth to make particularly detailed observations of the system.

These observations revealed that uniquely both the white dwarf stars in this pairing are composed largely of helium. Most white dwarfs tend to have largely inert cores of carbon and oxygen that have formed over the star's long life when it has used up most of its hydrogen and helium. Helium white dwarfs are a sure sign that the star has undergone some extreme mass loss at some point. To find two such helium white dwarfs stars is a clear sign to astronomers that both stars have had an exotic and mutually destructive past.

What was originally the most massive star of the pair had once actually began to expand to become a red giant but its outer hydrogen envelope was ripped off by its companion. This meant the star never got an opportunity to start fusing its helium and it was left as a helium white dwarf. When the companion star then began expanded it also had its expanding layer torn off by the first star -- but as the first star was already reduced to a white dwarf it could not use that new material. That hydrogen was therefore simply lost to the star system leaving behind helium white dwarfs.

In just over 1 billion years, the two stars feud will end as they will spiral together and merge, finally igniting each other's helium to become an object known as a hot subdwarf which should last for 100 million years.

The University of Warwick researchers found this star system CSS 41177 (which is over 351 parsecs , or 1140 light years, away -- in the constellation Leo) using a combination of data from the robotic 2m Liverpool Telescope in the Canary Islands and the 8m Gemini Telescope on Hawaii.

Story Source:

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

Journal Reference:

S. G. Parsons, T. R. Marsh, B. T. Gänsicke, A. J. Drake, D. Koester. A deeply eclipsing detached double helium white dwarf binary. Astrophysical Journal Letters, 2011; (accepted) [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.

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Feuding helium dwarf stars exposed by eclipse

ScienceDaily (May 24, 2011) — Researchers at the University of Warwick have found a unique feuding double white dwarf star system where each star appears to have been stripped down to just its helium.

Astronomers know of just over 50 close double white dwarfs, but this was only the second ever eclipsing close white dwarf pair to be found. The University of Warwick astronomers Steven Parsons and Professor Tom Marsh were able to use the fact that the stars eclipse each other when seen from Earth to make particularly detailed observations of the system.

These observations revealed that uniquely both the white dwarf stars in this pairing are composed largely of helium. Most white dwarfs tend to have largely inert cores of carbon and oxygen that have formed over the star's long life when it has used up most of its hydrogen and helium. Helium white dwarfs are a sure sign that the star has undergone some extreme mass loss at some point. To find two such helium white dwarfs stars is a clear sign to astronomers that both stars have had an exotic and mutually destructive past.

What was originally the most massive star of the pair had once actually began to expand to become a red giant but its outer hydrogen envelope was ripped off by its companion. This meant the star never got an opportunity to start fusing its helium and it was left as a helium white dwarf. When the companion star then began expanded it also had its expanding layer torn off by the first star -- but as the first star was already reduced to a white dwarf it could not use that new material. That hydrogen was therefore simply lost to the star system leaving behind helium white dwarfs.

In just over 1 billion years, the two stars feud will end as they will spiral together and merge, finally igniting each other's helium to become an object known as a hot subdwarf which should last for 100 million years.

The University of Warwick researchers found this star system CSS 41177 (which is over 351 parsecs , or 1140 light years, away -- in the constellation Leo) using a combination of data from the robotic 2m Liverpool Telescope in the Canary Islands and the 8m Gemini Telescope on Hawaii.

Story Source:

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

Journal Reference:

S. G. Parsons, T. R. Marsh, B. T. Gänsicke, A. J. Drake, D. Koester. A deeply eclipsing detached double helium white dwarf binary. Astrophysical Journal Letters, 2011; (accepted) [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

Shaking down frozen helium: In a 'supersolid' state, it has liquid-like characteristics

ScienceDaily (May 12, 2011) — In a four-decade, Holy Grail-like quest to fully understand what it means to be in a "supersolid" state, physicists have found that supersolid isn't always super solid. In other words, this exotic state of frozen helium appears to have liquid-like properties, says a new paper published in the journal Science.

Why is this important? Understanding supersolid helium brings us closer to understanding its close cousins superconductivity and superfluidity.

Physicists had long thought that the unusual behavior of torsion oscillators containing solid helium meant that chilling helium down to temperatures near absolute zero prompts its transformation into a supersolid. It is certainly solid, but in this physical quest, there was a nagging question: Is it a true supersolid?

To gain new perspectives on solid helium, new research tools were needed. "Think of this analogy: when Galileo first peered through a telescope, he saw ears on Saturn. With improved technology, humanity began to understand those ears were actually rings around the planet. And with better technology, we saw the differences in the rings. To further understand solid helium, science had to invent new approaches," says Séamus Davis, Cornell professor of physics. "Helium is a pure material. We're gaining a new understanding of the fundamental issues of how nature works, of how the universe works."

In fact, in this paper, the researchers show instead a more prosaic explanation: There are moving defects in the solid helium crystals, and their relaxation time falls with rising temperatures. This is more consistent with the torsional oscillation (shaking) experiments conducted at Cornell.

The researchers learned that the unusual properties of solid helium do not reflect a clunky transition between the solid state and a supersolid state. It behaves like a dimmer switch and presents a smooth transition near absolute zero.

Funding for this research: the National Science Foundation and the Kavli Institute for Theoretical Physics. Research at Los Alamos was supported by U.S. Department of Energy, through the Laboratory Directed Research and Development program.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Cornell University, via EurekAlert!, a service of AAAS.

Journal Reference:

E. J. Pratt, B. Hunt, V. Gadagkar, M. Yamashita, M. J. Graf, A. V. Balatsky, and J. C. Davis. Interplay of Rotational, Relaxational, and Shear Dynamics in Solid 4He. Science, 13 May 2011: Vol. 332 no. 6031 pp. 821-824 DOI: 10.1126/science.1203080

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.

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