Category: Astronomy

Physicists working to re-create the matter that existed at the birth of the universe expected something like a gas and ended up with the “perfect” liquid, four teams of researchers reported at an April 18 meeting of the American Physical Society. One of the teams is led by MIT.

“These truly stunning findings have led us to conclude that we are seeing something completely new–an unexpected form of matter–which is opening new avenues of thought about the fundamental properties of matter and the conditions that existed just after [the Big Bang],” said Raymond Orbach, director of the U.S. Department of Energy’s Office of Science, the primary supporter of the research.

Unlike ordinary liquids, in which individual molecules move about randomly, the new matter seems to move in a pattern that exhibits a high degree of coordination among the particles–something like a school of fish that responds as one entity while moving through a changing environment. That fluid motion is nearly “perfect,” as defined by the equations of hydrodynamics.

Picture a stream of honey, then a stream of water. “Water flows much more easily than honey, and the new liquid we’ve created seems to flow much more easily than water,” said Wit Busza, leader of the MIT team and the Francis Friedman Professor of Physics. Other MIT faculty involved in the work are Professor Bolek Wyslouch and Associate Professor Gunther Roland, both of physics.

Busza notes that the results don’t rule out that a gas-like form of matter existed at some point in the young universe, but the data do suggest “something different, and maybe even more interesting, at the lower energy densities created at RHIC (Relativistic Heavy Ion Collider).”

The research has also led to several other surprises. For example, “there is an elegance we see in the data that is not reflected in our theoretical understanding–yet,” said Roland.

Birth of the universe
About ten millionths of a second after the Big Bang, physicists believe that the universe was composed of a gas of weakly interacting objects, quarks and gluons that would ultimately clump together to form atomic nuclei and matter as we know it.

So, over the last 25 years, scientists have been working to re-create that gas, or quark-gluon plasma, by building ever-larger atom smashers. “The idea is to accelerate nuclei to nearly the speed of light, then have them crash head-on,” Busza said. “Under those conditions the plasma is expected to form.” The current results were achieved at the Relativistic Heavy Ion Collider located at the DOE’s Brookhaven National Laboratory.

RHIC accelerates gold nuclei in a circular tube some 2 kilometers in diameter. In four places the nuclei collide, and around those sites teams of scientists have built detectors to collect the data. The four instruments–STAR, PHENIX, PHOBOS and BRAHMS–vary in their approaches to tracking and analyzing particles’ behavior. The work reported at the APS meeting summarizes the first three years of RHIC results from all four devices. Papers from each team will also be published simultaneously in an upcoming issue of the journal Nuclear Physics A.

MIT is the lead institution for PHOBOS, a collaboration between the United States, Poland and Taiwan. “We are very small,” said Busza, who developed the concept for the device. “STAR and PHENIX each cost about $100 million and have some 400 staff. We cost less than $10 million and have about 50 people,” he said. (BRAHMS is also small.)

Nevertheless, the PHOBOS team got the first physics results from three of the five RHIC experimental runs and tied for first on a fourth. (The fifth run is still being analyzed.)

For one of those runs, the team collected the data, analyzed them and submitted a paper on the work all within five weeks. “That’s unheard of in high-energy physics,” said Busza, who credits Roland with the fast turnaround. “He was the person who managed the extraction of the physics from the data.”

What’s next?
Although the larger RHIC detectors will continue to collect data, PHOBOS has been retired. “From a cost-benefit perspective, we feel we’ve extracted as much knowledge as we can from such a small experiment,” Busza said.

So the team is now looking to the future. The members hope to continue their studies at RHIC’s successor, the Large Hadron Collider (LHC) being built in Europe. That facility will have 30 times the collision energy of RHIC, which will bring the scientists that much closer to the conditions at the birth of the universe. “At LHC we’ll test what we think we learned from RHIC,” Busza said. “We also expect new surprises, perhaps even bigger surprises,” he concluded.

MIT research staff currently involved in PHOBOS are Maarten Ballintijn, Piotr Kulinich, Christof Roland, George Stephans, Robin Verdier, Gerrit vanNieuwenhuizen and Constantin Loizides. Six graduate students are also on the team; the research has already resulted in five theses, with two on the way.

Original Source: MIT News Release

Image credit: ANU
A new star that may be one of the first to have formed in the Universe has been discovered by an international team led by ANU researchers.

The new star ? which goes by the innocuous name HE 1327-2326 ? is of enormous importance because it provides the crucial evidence of the time when the very first stars formed after the Big Bang.

?This star?s a record breaker ? it has the lowest levels of iron ever recorded in a star so far. This is of great importance because it indicates HE 1327-2326 formed in the very early Universe,? team leader and astronomy PhD student, Ms Anna Frebel said.

In general, stars with a low iron abundance compared to the Earth?s sun are called ?metal-poor? stars.

?Elements such as iron are only synthesised in the course of the lifetime of stars during the evolution of the Universe,? Ms Frebel said.

?Thus, we believe HE 1327-2326 formed shortly after the Big Bang ? it?s about twice as iron-poor as the previous record holder, HE 0107-5240, which was discovered in 2001 by ANU and German astronomers as part of the same survey.

?HE 1327-2326 will be used to trace the very early chemical enrichment history of the Universe as well as star formation processes and will challenge astronomers around the world ? it?s a pretty exciting prospect.?

The researchers first observed HE 1327-2326 using the European Southern Observatory?s 3.6-metre telescope in Chile. High quality data taken later with Japan?s 8-metre Subaru telescope in Hawaii revealed HE 1327-2326?s extraordinarily low iron content.

The star was discovered in a sample of about 1800 ?metal-poor? stars that are being investigated as part of Ms Frebel?s PhD project and is detailed in the latest edition of Nature in the paper Nucleosynthetic signatures of the first stars.

Research collaborators included Professor John Norris from the Research School of Astronomy and Astrophysics, Dr Wako Aoki from the National Astronomical Observatories of Japan and Dr Norbert Christlieb from Hamburger Sternwarte in Germany, as well as other researchers in Sweden, the US, the UK, Japan and Australia.

?HE 1327-2326 is a very unusual object in many ways for us astronomers,? Professor Norris, Ms Frebel?s supervisor, said. ?Relative to its iron levels has abnormally high levels of several elements including carbon, nitrogen and strontium.

?Another very interesting and unusual observation is that no lithium could be detected in the relatively unevolved star. A yet unknown process must have led to depletion of that element.

?Stars that formed later in the history of the Universe tend to have more predictable ratios of these elements,? Professor Norris said.

Ms Frebel said there could be several scenarios that explain the unusual features of HE 1327-2326.

?An explanation could be that only one explosion of one of the first stars in the Universe happened, which led to pollution of the surrounding gas cloud with elements heavier than hydrogen, helium and lithium in which stars like HE 1327-2326 might have formed,? she said.

?However, it can not be excluded that HE 1327-2326 formed just after the Big Bang and there was little time for the iron content to develop and therefore is actually one of the ?first stars? itself ? although as yet no genuine ?first star? has been found.?

Original Source: ANU News Release

Recent spectroscopic studies of infrared light reflected from the surface of Sedna reveal that it is probably unlike Pluto and Charon since Sedna’s surface does not display evidence for a large amount of either water or methane ice. Due to Sedna?s extreme distance from the Sun, the frigid surface has probably been untouched for millions of years by anything except cosmic rays and solar ultraviolet radiation.

Gemini Observatory astronomer Chad Trujillo led an effort by the same California Institute of Technology research team responsible for Sedna’s original discovery to obtain spectra of this distant planetoid using the Near Infrared Imager (NIRI) on Gemini North. Their aim was to better understand the surface of this distant world and how it has evolved since its formation. ?It is likely that Sedna has experienced an extremely isolated life in the outskirts of our solar system,? said Trujillo. ?Out there beyond what we used to think was the edge of the solar system, interactions or collisions between bodies are probably very rare. Our observations confirm what you would expect from a surface that has been so far out in our solar system for such a long time and exposed to space weathering.?

The Sedna data lack the strong spectral lines that would indicate the existence of substances like methane and water ice, but deeper studies are needed to confirm how low the levels of these ices might be on this planetoid. Sedna might be more like the minor planet Pholus (that lies just inside the orbit of Saturn), which is similar in its redness in visible light. This same ?space weathering? may also affect Pluto and Charon, but there may be other processes that replenish their water- and methane-rich surfaces, such as atmospheric effects, geological processes and collisions.

The data could reveal something of Sedna’s evolutionary history in the outer solar system. Astronomers think that objects like Sedna start out with icy surfaces. Over time cosmic rays and solar ultraviolet radiation ?bake and burn? the surfaces into black hydrocarbon-rich substances similar to asphalt, which do not reveal themselves well in infrared spectra. Such a history might explain why Sedna doesn’t exhibit traces of methane and water ice, whereas Pluto and Charon do.

?Like a sandblaster operating for several billion years, most of the objects out as far as Pluto are constantly being resurfaced by impacts and collisions which expose and supply fresh surface materials before the black stuff can get baked on,? said Michael Brown of California Institute of Technology, who is the Principle Investigator of the team that originally discovered Sedna. ?Pluto and its moon Charon provide an excellent example of this process, with Pluto displaying a strong methane ice signature in its spectrum and Charon dominated by water ice.?

The team does not rule out the possibility that longer-duration (deeper) observations might reveal evidence of methane or water ice on Sedna. However, the Gemini data indicate that if they do exist their extent is limited.

The results of these observations will appear in The Astrophysical Journal.

Original Source: Gemini News Release

Most Milky Way stars – such as our own Sun – move in millions-of-years-long near-circular orbits unperturbed by the super-massive black hole (SMBH) in the midst of the galaxy. But at Milky Way Central stars can display unusually frenetic and highly eccentric motions. Those closest to the SMBH spend most of their time near aphelion – well away from its event horizon. But the SMBH’s relentless gravitational grip soon draws them inward again toward perihelion. As these stars lose their footing in the SMBH’s gravity well, they accelerate rapidly – only escaping total dissolution due to their extremely high orbital angular momentum.

Such “S-stars” were first identified by two independent teams of astronomers (one led by Reinhard Genzel at the Max Planck Institute in Garching, Germany, and the other by Andrea Ghez at UCLA) in 2002. Due to high concentrations of gas and dust enshrouding the galactic core, the teams had to detect these highly mobile sources using infrared light. By looking for shifts in the spectra of the stars and determining how fast they moved in relationship to other objects, precise orbits could be obtained. In the three years since their discovery one S-star (S2) has nearly finished a complete orbit of the Milky Way’s SMBH.

But there is something very peculiar about S-stars. Based on current models of stellar evolution, these stars should be very old – but have somehow managed to retain all the characteristics of youth.

Theoretical astronomers Melvyn Davies of Lund Observatory, Sweden and Andrew King of the University of Leicester, United Kingdom have an answer: “Our picture simultaneously explains why S-stars have tightly-bound orbits, and the observed depletion of red giants in the very center of the Galaxy.” Most stars seen around us (outside Milky Way Central) have well understood life cycles. These stars pass through a “main sequence” of development – originating as large, low-temperature bodies with smoldering central fusion furnaces and ending as small white dwarves radiating “heat” as visible light while quietly chilling out in the twilight of their celestial careers.

A star’s destiny is primarily determined by its mass. Super-massive stars, (as great as 150 Suns) live very fast lives and survive for as little as fifty thousand years. During their youth, these stars exult as brilliant blue giants with surface temperatures as high as 30,000 degrees C. Meanwhile more modest stars such as the Sun live much longer, glowing temperately for 5 to 15 billion years at lower surface temperatures (5,000 – 10,000 degrees C). Within all stars nuclear furnaces provide the energy needed to create visible light. As a star matures, its nuclear furnace grows in surface area and it gives off more and more radiation. At a certain point core radiation pressure becomes so intense that the outer atmosphere of the star swells many times over. This diffuse low- temperature gaseous envelope tells astronomers that a star is well-advanced in age and is approaching the end of its life-cycle.

But there are no such “red-giants” among the S-stars at Milky Way Central.

All stars are birthed in clusters and form associations. This should include S-stars near the SMBH. Star clusters precipitate as a group out of large regions of nebular dust and primordial gas. Although cluster stars are bound together gravitationally, tidal forces from the center of the galaxy can tear them apart over millions of years. Individual stars within such clusters then spiral inward toward the core of the galaxy. As this occurs, these stars should age to become “stars within stars” – highly radiant blue stellar cores enshrouded by hugely swollen gaseous red-giant envelopes. In their paper “The Stars of the Galactic Center” (published March 21, 2005) the authors go on to say: “S stars orbit in a region where tidal forces from the central super-massive black hole prevent star formation.”

According to current astronomical thinking S-stars should also form in clusters, and these clusters must originate well away from tidal forces near the galaxy core. It is possible, of course, for S-stars to have a different birth cycle from other stars. One idea explored by theorists is that core S-stars form as a result of recent collisions between dense molecular clouds near Milky Way Central. Another notion is that they may be spun out of the accretion disk surrounding the SMBH itself. To account for their luminosity, and high temperatures (30K degrees C), S-stars must have intermediate masses (~10 solar) and live relatively short life cycles (~10 Myrs). Because of these constraints core S-stars must all be relatively young and new ones must form constantly.

“A plausible alternative picture is that S-stars result from the sinking of massive stellar clusters toward the black hole by dynamical friction. However tides disrupt such clusters at distances much further out than the region of the observed S-stars. To supply the S-stars requires scattering into near radial orbits by gravitational interactions with other stars. However this process occurs on a timescale which would considerably exceed the main-sequence lifetime of such stars of the observed temperatures.” writes the pair.

Effectively, core S-stars must either be very youthful and delivered into the region of the SMBH by some unknown mechanism, or they must be much older than thought and somehow rendered “youthful” by interacting with the black hole and its immediate environs. Could there be a “fountain of stellar youth” at the center of the Milky Way Galaxy?

“Stripping stars solves the birth problem.”, says the authors. “… the only stars potentially identifiable as Galactic Center red giants lose their envelopes and turn into S stars instead.” Core S-stars have gone through a process of cluster birth and maturation similar to our Sun. Because they may be less massive than once thought (~ 1-4 solar masses), they’ve had more time to move toward the core.

Driven inward by gravitational scattering from more massive stars, these aging red giants receive a cosmic “face-lift” – as black hole tidal forces strip away their outer shrouds to join other gases fueling the SMBH itself. Because of greater than once thought longevity, these lower mass stars have had ample time to arrive at the galactic core from more distant clusters. The fact that they have lost their shrouds explains their relative brilliance, high temperatures, and apparent youth.

Does our own Sun have such a future before it?

According to Melvyn Davies, “No, the sun won’t suffer the same fate. We are too far from the galactic center. We are about 30000 light years from the black hole; the stars getting scattered in have come from much closer in, certainly no further than about 3000 light years.” Professor Andrew King adds, “The Sun has no close companion which could disturb its normal evolution. So it will eventually become a red giant and evolve into a run-of-the-mill white dwarf.”

Well, it would appear that there is no fountain of youth in the center of the galaxy for Sol after all.

Written by Jeff Barbour

Astronomers using the National Science Foundation’s Very Long Baseline Array (VLBA) radio telescope have tracked the motion of a violent region where the powerful winds of two giant stars slam into each other. The collision region moves as the stars, part of a binary pair, orbit each other, and the precise measurement of its motion was the key to unlocking vital new information about the stars and their winds.

Both stars are much more massive than the Sun — one about 20 times the mass of the Sun and the other about 50 times the Sun’s mass. The 20-solar-mass star is a type called a Wolf-Rayet star, characterized by a very strong wind of particles propelled outward from its surface. The more massive star also has a strong outward wind, but one less intense than that of the Wolf-Rayet star. The two stars, part of a system named WR 140, circle each other in an elliptical orbit roughly the size of our Solar System.

“The spectacular feature of this system is the region where the stars’ winds collide, producing bright radio emission. We have been able to track this collision region as it moves with the orbits of the stars,” said Sean Dougherty, an astronomer at the Herzberg Institute for Astrophysics in Canada. Dougherty and his colleagues presented their findings in the April 10 edition of the Astrophysical Journal.

The supersharp radio “vision” of the continent-wide VLBA allowed the scientists to measure the motion of the wind collision region and then to determine the details of the stars’ orbits and an accurate distance to the system.

“Our new calculations of the orbital details and the distance are vitally important to understanding the nature of these Wolf-Rayet stars and of the wind-collision region,” Dougherty said.

The stars in WR 140 complete an orbital cycle in 7.9 years. The astronomers tracked the system for a year and a half, noting dramatic changes in the wind collision region.

“People have worked out theoretical models for these collision regions, but the models don’t seem to fit what our observations have shown,” said Mark Claussen, of the National Radio Astronomy Observatory in Socorro, New Mexico. “The new data on this system should provide the theorists with much better information for refining their models of how Wolf-Rayet stars evolve and how wind-collision regions work,” Claussen added.

The scientists watched the changes in the stellar system as the star’s orbits carried them in paths that bring them nearly as close to each other as Mars is to the Sun and as far as Neptune is from the Sun. Their detailed analysis gave them new information on the Wolf-Rayet star’s strong wind. At some points in the orbit, the wind collision region strongly emitted radio waves, and at other points, the scientists could not detect the collison region.

Wolf-Rayet stars are giant stars nearing the time when they will explode as supernovae.

“No other telescope in the world can see the details revealed by the VLBA,” Claussen said. “This unmatched ability allowed us to determine the masses and other properties of the stars, and will help us answer some basic questions about the nature of Wolf-Rayet stars and how they develop.” he added.

The astronomers plan to continue observing WR 140 to follow the system’s changes as the two massive stars continue to circle each other.

Dougherty and Claussen worked with Anthony Beasley of the Atacama Large Millimeter Array office, Ashley Zauderer of the University of Maryland and Nick Bolingbroke of the University of Victoria, British Columbia.

Original Source: NRAO News Release

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Remember Sedna? It’s that icy object uncovered last year in the outer reaches of the Solar System. When it was first discovered, astronomers noticed it rotated once every 20 days. The only explanation that could explain this slow rotation was a moon, but a moon never showed up in any of their observations. Scott Gaudi is a researcher with the Harvard Smithsonian Centre for Astrophysics. He and his colleagues have been watching the rotation of Sedna with a skeptical eye, and think it’s only rotating once every 10 hours or so. As for the moon? Easy come, easy go.
Continue reading “Podcast: Sedna Loses Its Moon”

Image credit: NRAO
Astronomers using the National Science Foundation’s Very Large Array (VLA) radio telescope are taking advantage of a once-in-a-lifetime opportunity to watch an old star suddenly stir back into new activity after coming to the end of its normal life. Their surprising results have forced them to change their ideas of how such an old, white dwarf star can re-ignite its nuclear furnace for one final blast of energy.

Computer simulations had predicted a series of events that would follow such a re-ignition of fusion reactions, but the star didn’t follow the script — events moved 100 times more quickly than the simulations predicted.

“We’ve now produced a new theoretical model of how this process works, and the VLA observations have provided the first evidence supporting our new model,” said Albert Zijlstra, of the University of Manchester in the United Kingdom. Zijlstra and his colleagues presented their findings in the April 8 issue of the journal Science.

The astronomers studied a star known as V4334 Sgr, in the constellation Sagittarius. It is better known as “Sakurai’s Object,” after Japanese amateur astronomer Yukio Sakurai, who discovered it on February 20, 1996, when it suddenly burst into new brightness. At first, astronomers thought the outburst was a common nova explosion, but further study showed that Sakurai’s Object was anything but common.

The star is an old white dwarf that had run out of hydrogen fuel for nuclear fusion reactions in its core. Astronomers believe that some such stars can undergo a final burst of fusion in a shell of helium that surrounds a core of heavier nuclei such as carbon and oxygen. However, the outburst of Sakurai’s Object is the first such blast seen in modern times. Stellar outbursts observed in 1670 and 1918 may have been caused by the same phenomenon.

Astronomers expect the Sun to become a white dwarf in about five billion years. A white dwarf is a dense core left after a star’s normal, fusion-powered life has ended. A teaspoon of white dwarf material would weigh about 10 tons. White dwarfs can have masses up to 1.4 times that of the Sun; larger stars collapse at the end of their lives into even-denser neutron stars or black holes.

Computer simulations indicated that heat-spurred convection (or “boiling”) would bring hydrogen from the star’s outer envelope down into the helium shell, driving a brief flash of new nuclear fusion. This would cause a sudden increase in brightness. The original computer models suggested a sequence of observable events that would occur over a few hundred years.

“Sakurai’s object went through the first phases of this sequence in just a few years — 100 times faster than we expected — so we had to revise our models,” Zijlstra said.

The revised models predicted that the star should rapidly reheat and begin to ionize gases in its surrounding region. “This is what we now see in our latest VLA observations,” Zijlstra said.

“It’s important to understand this process. Sakurai’s Object has ejected a large amount of the carbon from its inner core into space, both in the form of gas and dust grains. These will find their way into regions of space where new stars form, and the dust grains may become incorporated in new planets. Some carbon grains found in a meteorite show isotope ratios identical to those found in Sakurai’s Object, and we think they may have come from such an event. Our results suggest this source for cosmic carbon may be far more important than we suspected before,” Zijlstra added.

The scientists continue to observe Sakurai’s Object to take advantage of the rare opportunity to learn about the process of re-ignition. They are making new VLA observations just this month. Their new models predict that the star will heat very quickly, then slowly cool again, cooling back to its current temperature about the year 2200. They think there will be one more reheating episode before it starts its final cooling to a stellar cinder.

Zijlstra worked with Marcin Hajduk of the University of Manchester and Nikolaus Copernicus University, Torun, Poland; Falk Herwig of Los Alamos National Laboratory; Peter A.M. van Hoof of Queen’s University in Belfast and the Royal Observatory of Belgium; Florian Kerber of the European Southern Observatory in Germany; Stefan Kimeswenger of the University of Innsbruck, Austria; Don Pollacco of Queen’s University in Belfast; Aneurin Evans of Keele University in Staffordshire, UK; Jose Lopez of the National Autonomous University of Mexico in Ensenada; Myfanwy Bryce of Jodrell Bank Observatory in the UK; Stewart P.S. Eyres of the University of Central Lancashire in the UK; and Mikako Matsuura of the University of Manchester.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Original Source: NRAO News Release

Astronomers have found a vast loop-like structure, 20 light years across, adjacent to the most massive star-forming region known in our galaxy. The loop, which was observed in X-ray wavelengths, is 15 times the size of the Arches Cluster, a star-forming region close to the centre of the Milky Way. This is the first time that such a distinctive and huge loop structure has been observed. Dr Masaaki Sakano, from the University of Leicester, will be presenting the discovery at the RAS National Astronomy Meeting at the University of Birmingham on Friday 8th April.

The team of astronomers, which includes scientists from the University of Leicester, CEA Saclay and the Max Planke Institute for Extraterrestrial Physics, observed the Arches Cluster repeatedly using the European X-ray satellite, XMM-Newton, as a part of the XMM-Newton Galactic Centre Survey. The galactic centre can only be observed at certain wavelengths, such as X-rays, because large amounts of dust lie in our line of sight and this blocks out optical light.

Dr Sakano says, “The X-ray spectrum of the loop is extraordinary. Most diffuse X-ray sources in the Universe have a characteristic temperature because they are the residual radiation from an event, such as a supernova explosion. However in this case the loop is non-thermal and this means that whatever the origin of the structure is, it is not stationary but rather the result of some ongoing process.”

The most straightforward interpretation of the observations is that powerful particle-acceleration is occurring on-site, producing high energy particles with an energy of up to a thousand trillion electron volts (a thousand times more energetic than those produced in man-made particle accelerators). Such particles have been detected previously in a few supernova remnants and many pulsar nebulae, where a very powerful central source has created them. However, evidence for high-energy particles has never been observed before in star-forming regions of our galaxy.

At this stage it is not clear whether the loop structure is physically related to the Arches Cluster or just happens to be in our line of sight. However, if future observations show that the Arches Cluster is responsible for the feature, this discovery suggests that star-forming activity plays an important role in the energetic Universe.

Original Source: RAS News Release