Astronomers find bounty of failed stars: One youngster only six times heftier than Jupiter

ScienceDaily (Oct. 11, 2011) — A University of Toronto-led team of astronomers has discovered over two dozen new free-floating brown dwarfs, including a lightweight youngster only about six times heftier than Jupiter, that reside in two young star clusters. What's more, one cluster contains a surprising surplus of them, harbouring half as many of these astronomical oddballs as normal stars.

"Our findings suggest once again that objects not much bigger than Jupiter could form the same way as stars do. In other words, nature appears to have more than one trick up its sleeve for producing planetary mass objects," says Professor Ray Jayawardhana, Canada Research Chair in Observational Astrophysics at the University of Toronto and leader of the international team that made the discovery.

Brown dwarfs straddle the boundary between stars and planets. Sometimes described as failed stars, they glow brightly when young, from the heat of formation, but cool down over time and end up with atmospheres that exhibit planet-like characteristics. Scientists think that most brown dwarfs may have formed like stars, in isolation from contracting gas clouds, but some of the puniest free-floaters may have formed like planets around a star and later ejected.

The findings come from observations using the Subaru Telescope in Hawaii and the Very Large Telescope (VLT) in Chile during the Substellar Objects in Nearby Young Clusters (SONYC) survey. Astronomers took extremely deep images of the NGC 1333 and rho Ophiuchi star clusters with Subaru at both optical and infrared wavelengths. Once they identified candidate brown dwarfs from the very red colors, the research team confirmed them with spectra taken at Subaru and the VLT. The team's findings will be reported in two upcoming papers in the Astrophysical Journal and presented this week at a scientific conference in Garching, Germany.

The six-Jupiter-mass brown dwarf found in the NGC 1333 cluster is one of the least massive free-floating objects known. "Its mass is comparable to those of giant planets, yet it doesn't circle a star. How it formed is a mystery," said Aleks Scholz of the Dublin Institute of Advanced Studies in Ireland, lead author of one paper and a former postdoctoral fellow at the University of Toronto.

Several other newly identified brown dwarfs in both NGC 1333 and rho Ophiuchi clusters have masses below 20 times that of Jupiter.

"Brown dwarfs seem to be more common in NGC 1333 than in other young star clusters. That difference may be hinting at how different environmental conditions affect their formation," says University of Toronto's Koraljka Muzic, lead author of the second paper.

"We could not have made these exciting discoveries if not for the remarkable capabilities of Subaru and the VLT. Instruments that can image large patches of the sky and take hundreds of spectra at once are key to our success," said co-author Motohide Tamura of the National Astronomical Observatory of Japan.

Other co-authors of the two papers are Vincent Geers of ETH Zurich in Switzerland, also a former UofT postdoc, and Mariangela Bonavita of the University of Toronto.

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One clock with two times: When quantum mechanics meets general relativity

ScienceDaily (Oct. 20, 2011) — The unification of quantum mechanics and Einstein's general relativity is one of the most exciting and still open questions in modern physics. General relativity, the joint theory of gravity, space and time gives predictions that become clearly evident on a cosmic scale of stars and galaxies. Quantum effects, on the other hand, are fragile and are typically observed on small scales, e.g. when considering single particles and atoms. That is why it is very hard to test the interplay between quantum mechanics and general relativity.

Now theoretical physicists led by Caslav Brukner at the University of Vienna propose a novel experiment which can probe the overlap of the two theories. The focus of the work is to measure the general relativistic notion of time on a quantum scale.

The findings were recently published in Nature Communications.

Time in general relativity

One of the counterintuitive predictions of Einstein's general relativity is that gravity distorts the flow of time. The theory predicts that clocks tick slower near a massive body and tick faster the further they are away from the mass. This effect results in a so-called "twin paradox": if one twin moves out to live at a higher altitude, he will age faster than the other twin who remains on the ground. This effect has been precisely verified in classical experiments, but not in conjunction with quantum effects, which is the aim of the newly proposed experiment.

Quantum interference and complementarity

The Viennese group of researchers wants to exploit the extraordinary possibility that a single quantum particle can lose the classical property of having a well-defined position, or as phrased in quantum mechanical terms: it can be in a "superposition." This allows for wave-like effects, called interference, with a single particle. However, if the position of the particle is measured, or even if it can in principle be known, this effect is lost. In other words, it is not possible to observe interference and simultaneously know the position of the particle. Such a connection between information and interference is an example of quantum complementarity -- a principle proposed by Niels Bohr. The experimental proposal now published in "Nature Communications" combines this principle with the "twin paradox" of general relativity.

Einstein's "twin paradox" for a quantum "only child"

The team at the University of Vienna considers a single clock (any particle with evolving internal degrees of freedom such as spin) which is brought in a superposition of two locations -- one closer and one further away from the surface of Earth. According to general relativity, the clock ticks at different rates in the two locations, in the same way as the two twins would age differently. But since the time measured by the clock reveals the information on where the clock was located, the interference and the wave-nature of the clock is lost. "It is the twin paradox for a quantum 'only child', and it requires general relativity as well as quantum mechanics. Such an interplay between the two theories has never been probed in experiments yet" -- says Magdalena Zych, the lead author of the paper and member of the Vienna Doctoral Program CoQuS. It is therefore the first proposal for an experiment that allows testing the genuine general relativistic notion of time in conjunction with quantum complementarity.

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Magdalena Zych, Fabio Costa, Igor Pikovski, Caslav Brukner. Quantum interferometric visibility as a witness of general relativistic proper time. Nature Communications, 2011; 2: 505 DOI: 10.1038/ncomms1498

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Model finds optimal fiber optic network connections 10,000 times more quickly

ScienceDaily (June 28, 2011) — Designing fiber optic networks involves finding the most efficient way to connect phones and computers that are in different places -- a costly and time-consuming process. Now researchers from North Carolina State University have developed a model that can find optimal connections 10,000 times more quickly, using less computing power to solve the problem.

"Problems that used to take days to solve can now be solved in just a few seconds," says Dr. George Rouskas, computer science professor at NC State and author of a paper describing the new method. The model could solve problems more than 10,000 times faster when data is routed through larger "rings," in the network, Rouskas says.

Every time you make a phone call or visit a website, you send and receive data in the form of wavelengths of light through a network of fiber optic cables. These data are often routed through rings that ensure the information gets where it needs to go. These ring networks are faced with the constant challenge of ensuring that their system design can meet user requirements efficiently. As a result, ring network designers try to determine the best fiber optic cable route for transmitting user data between two points, as well as which wavelength of light to use. Most commercial fiber optics handle approximately 100 different wavelengths of light.

Solving these design challenges is difficult and time-consuming. Using existing techniques, finding the optimal solution for a ring can take days, even for smaller rings. And a ring's connections are modified on an ongoing basis, to respond to changing use patterns and constantly increasing traffic demands.

But the new model developed by Rouskas and his team should speed things up considerably. Specifically, the researchers have designed a mathematical model that identifies the exact optimal routes and wavelengths for ring network designers. The model creates a large graph of all the paths in a ring, and where those paths overlap. The model then breaks that graph into smaller units, with each unit consisting of the paths in a ring that do not overlap. Because these paths do not overlap, they can use the same wavelengths of light. Paths that overlap cannot use the same wavelengths of light -- because two things cannot occupy the same space at the same time.

By breaking all of the potential paths down into these smaller groups, the model is able to identify the optimal path and wavelength between two points much more efficiently than previous techniques.

"This will significantly shorten the cycle of feedback and re-design for existing rings," Rouskas says. "It also means that the ring design work can be done using fewer computer resources, which makes it less expensive. This should allow network providers to be more responsive to user demands than ever before."

The paper, "Fast Exact ILP Decompositions for Ring RWA," is published in the July issue of the Journal of Optical Communications and Networking. The paper was co-authored by Dr. Emre Yetginer, a former postdoctoral researcher at NC State now at Tubitak UEKAE, and NC State Ph.D. student Zeyu Liu.

NC State's Department of Computer Science is part of the university's College of Engineering.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by North Carolina State University.

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Emre Yetginer, Zeyu Liu, George N. Rouskas. Fast Exact ILP Decompositions for Ring RWA. Journal of Optical Communications and Networking, 2011; 3 (7): 577 DOI: 10.1364/JOCN.3.000577

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