Category: Astronomy

Astronomers studying data from the National Science Foundation’s Very Long Baseline Array (VLBA) and other telescopes have concluded that a binary pair of stars forming an energetic microquasar was blasted out of the cluster in which it was born by a supernova explosion some 1.7 million years ago. This is the first time that a fast-moving stellar pair has been tracked back to a specific star cluster.

The scientists analyzed numerous observations of a microquasar called LSI +61 303, and concluded that it is moving away from a star cluster named IC 1805 at nearly 17 miles per second.

A microquasar is a pair of stars, one of which is either a dense neutron star or a black hole, in which material sucked from a “normal” star forms a rapidly-rotating disk around the denser object. The disk becomes so hot it emits X-rays, and also spits out “jets” of subatomic particles at nearly the speed of light.

“In this case, both the microquasar and the star cluster are about 7,500 light-years from Earth and the characteristics of the ‘normal’ star in the microquasar match those of the other stars in the cluster, so we feel confident that the microquasar was shot out from a birthplace in this cluster,” said Felix Mirabel, an astrophysicist at the Institute for Astronomy and Space Physics of Argentina and French Atomic Energy Commission. Mirabel worked with Irapuan Rodrigues, of the Federal University of Rio Grande do Sul, Brazil, and Qingzhong Liu of the Purple Mountain Observatory in Nanjing, China. The astronomers reported their results in the August 1 issue of the scientific journal Astronomy & Astrophysics.

Many neutron stars have been found to be moving rapidly through the sky, leading scientists to conclude that the supernova explosions that produced them were asymmetric, giving a “kick” to the star. LSI +61 303’s motion has carried it about 130 light-years from the cluster IC 1805. The cluster is in the constellation Cassiopeia.

LSI +61 303 contains, the astronomers say, either a black hole or a neutron star with twice the mass of the Sun, orbiting a normal star 14 times more massive than the Sun every 26.5 days. The supernova explosion that produced the black hole or neutron star blew away about twice the mass of the Sun.

The black hole or neutron star originally was much more massive than its companion. The scientists still are unsure about how massive it was. Some evidence, they say, indicates that it was formed only four or five million years ago and exploded a million or so years ago. In that case, the star would have been 60 or more times more massive than the Sun, and would have expelled some 90 percent of its initial mass before the supernova explosion.

On the other hand, they say, the star may have formed some 10 million years ago, in which case it would have been 15-20 times more massive than the Sun.

“Studying this system and hopefully others like it that may be found will help us to understand both the evolution of stars before they explode as supernovae and the physics of the supernova explosions themselves,” Mirabel said.

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

Two of the biggest physics breakthroughs during the last decade are the discovery that wispy subatomic particles called neutrinos actually have a small amount of mass and the detection that the expansion of the universe is actually picking up speed.

Now three University of Washington physicists are suggesting the two discoveries are integrally linked through one of the strangest features of the universe, dark energy, a linkage they say could be caused by a previously unrecognized subatomic particle they call the “acceleron.”

Dark energy was negligible in the early universe, but now it accounts for about 70 percent of the cosmos. Understanding the phenomenon could help to explain why someday, long in the future, the universe will expand so much that no other stars or galaxies will be visible in our night sky, and ultimately it could help scientists discern whether expansion of the universe will go on indefinitely.

In this new theory, neutrinos are influenced by a new force resulting from their interactions with accelerons. Dark energy results as the universe tries to pull neutrinos apart, yielding a tension like that in stretched rubber band, said Ann Nelson, a UW physics professor. That tension fuels the expansion of the universe, she said.

Neutrinos are created by the trillions in the nuclear furnaces of stars such as our sun. They stream through the universe, and billions pass through all matter, including people, every second. Besides a minuscule mass, they have no electrical charge, which means they interact very little, if at all, with the materials they pass through.

But the interaction between accelerons and other matter is even weaker, Nelson said, which is why those particles have not yet been seen by sophisticated detectors. However, in the new theory, accelerons exhibit a force that can influence neutrinos, a force she believes can be detected by a variety of neutrino experiments already operating around the world.

“There are many models of dark energy, but the tests are mostly limited to cosmology, in particular measuring the rate of expansion of the universe. Because this involves observing very distant objects, it is very difficult to make such a measurement precisely,” Nelson said.

“This is the only model that gives us some meaningful way to do experiments on earth to find the force that gives rise to dark energy. We can do this using existing neutrino experiments.”

The new theory is advanced in a paper by Nelson; David Kaplan, also a UW physics professor; and Neal Weiner, a UW research associate in physics. Their work, supported in part by a grant from the U.S. Department of Energy, is detailed in a paper accepted for publication in an upcoming issue of Physical Review Letters, a journal of the American Physical Society.

The researchers say a neutrino’s mass can actually change according to the environment through which it is passing, in the same way the appearance of light changes depending on whether it’s traveling through air, water or a prism. That means that neutrino detectors can come up with somewhat different findings depending on where they are and what surrounds them.

But if neutrinos are a component of dark energy, that suggests the existence of a force that would reconcile anomalies among the various experiments, Nelson said. The existence of that force, made up of both neutrinos and accelerons, will continue to fuel the expansion of the universe, she said.

Physicists have pursued evidence that could tell whether the universe will continue to expand indefinitely or come to an abrupt halt and collapse on itself in a so-called “big crunch.” While the new theory doesn’t prescribe a “big crunch,” Nelson said, it does mean that at some point the expansion will stop getting faster.

“In our theory, eventually the neutrinos would get too far apart and become too massive to be influenced by the effect of dark energy any more, so the acceleration of the expansion would have to stop,” she said. “The universe could continue to expand, but at an ever-decreasing rate.”

Original Source: University of Washington News Release

While rovers and orbiting spacecraft scour Mars searching for clues to its past, researchers have uncovered another piece of the red planet in the most inhospitable place on Earth — Antarctica.

The new specimen was found by a field party from the U.S. Antarctic Search for Meteorites program (ANSMET) on Dec. 15, 2003, on an ice field in the Miller Range of the Transantarctic Mountains, roughly 750 km (466 miles) from the South Pole. This 715.2-gram (1.6-pound) black rock, officially designated MIL 03346, was one of 1358 meteorites collected by ANSMET during the 2003-2004 austral summer.

Discovery of this meteorite occurred during the second full field season of a cooperative effort funded by NASA and supported by the National Science Foundation (NSF) to enhance recovery of rare meteorite types in Antarctica, in the hopes new martian samples would be found.

Scientists at the Smithsonian Institution’s National Museum of Natural History involved in classification of Antarctic finds said the mineralogy, texture and the oxidized nature of the rock are unmistakably martian. The new specimen is the seventh recognized member of a group of martian meteorites called the nakhlites, named after the first known specimen that fell in Nakhla, Egypt, in 1911.

Like the other martian meteorites, MIL 03346 is a piece of the red planet that can be studied in detail in the laboratory, providing a critical “reality check” for use in interpreting the wealth of images and data being returned by the spacecraft currently exploring Mars. Following the existing protocols of the U.S. Antarctic meteorite program, scientists from around the world will be invited to request samples of the new specimen for their own detailed research.

Nakhlites are significant among the known martian meteorites for several reasons. Thought to have originated within thick lava flows that crystallized on Mars approximately 1.3 billion years ago, and sent to Earth by a meteorite impact about 11 million years ago, the nakhlites are among the older known martian meteorites. As a result they bear witness to significant segments of the volcanic and environmental history of Mars.

The U.S. Antarctic Meteorite program is a cooperative effort jointly supported by NSF, NASA and the Smithsonian Institution. Antarctic field work is supported by grants from NASA and NSF to Case Western Reserve University, Cleveland; initial examination and curation of recovered Antarctic meteorites is supported by NASA at the astromaterials curation facilities at Johnson Space Center in Houston; and initial characterization and long-term curation of Antarctic meteorite samples is supported by NASA and the Smithsonian Institution at the National Museum of Natural History in Washington.

Details concerning initial characterization of the specimen and sample availability are available through a special edition of the Antarctic Meteorite Newsletter, to be immediately released on the Web at:

Antarctic Meteorite Newsletter

Original Source: NASA News Release

Using observations of 3,000 quasars discovered by the Sloan Digital Sky Survey (SDSS), scientists have made the most precise measurement to date of the cosmic clustering of diffuse hydrogen gas. These quasars–100 times more than have been used in such analyses in the past–are at distances of eight to ten billion light years, making them among the most distant objects known.

Filaments of gas between the quasars and the Earth absorb light in the quasar’s spectra, allowing researchers to map the gas distribution and to measure how clumpy the gas is on scales of one million light years. The degree of clumping of this gas, in turn, can answer fundamental questions such as whether neutrinos have mass and what the nature of dark energy is, hypothesized to be driving the accelerated expansion of the universe.

“Scientists have long studied the clustering of galaxies to learn about cosmology,” explained Uros Seljak of Princeton University, one of the SDSS researchers. “However, the physics of galaxy formation and clustering is very complicated. In particular, because most of the mass of the universe is made up of dark matter, an uncertainty arises from our lack of understanding of the relation between the distribution of galaxies (which we see) and the dark matter (which we can’t see but the cosmological models predict).” The gas filaments seen in the quasar spectra are thought to be distributed very much like the dark matter, removing this source of uncertainty.

“We have known for several years that quasar spectra are a unique tool for studying the distribution of dark matter in the early universe, but the quantity and quality of the SDSS data have made that vision a reality,” said David Weinberg of Ohio State University, a member of the SDSS team. “It’s amazing that we can learn so much about the structure of the universe 10 billion years ago.”

Seljak and his collaborators on the SDSS combined the analysis of the quasar spectra with measurements of galaxy clustering, gravitational lensing, and ripples in the Cosmic Microwave Background observed by NASA’s Wilkinson Microwave Anisotropy Probe (WMAP). This gives the best determination to date of the clustering of matter in the universe from scales of one million light years to many billions of light years. This comprensive view allows detailed comparison with theoretical models for the history and constituents of the universe.

“This is the most rigorous test to date of the predictions of the cosmological model of inflation; inflation passes with flying colors,” added Seljak.

Inflationary theory states that right after the Big Bang the universe underwent a period of extremely rapid acceleration, during which tiny fluctuations were transformed into astronomical-sized wrinkles in space-time, ultimately observable in the clumping of astronomical objects. The theory of inflation predicts a very specific dependence of the degree of clustering with scale, which the current analysis strongly supports. Other scenarios, such as the cyclic universe theory, make very similar predictions and are also in agreement with the latest results.

Early analyses by the WMAP team and others had hinted at deviations in cosmic clustering from the prediction of inflation. If correct, this would have required a major revision of the current paradigm for origin of structure in the universe.

“The new data and the corresponding analysis substantially improves the observational precision of this test,” said Patrick McDonald of Princeton University and one of the finding’s authors. “The new results are in nearly perfect agreement with inflation.”

“The clustering of matter is a precise and powerful test of cosmological models, and the present analysis is consistent with, and extends our previous studies,” agreed Adrian Pope of The Johns Hopkins University, who led an earlier analysis of the clustering of SDSS galaxies.

The new analysis also provides the best information on the mass of the neutrino. Terrestial experiments–resulting in the 2002 Nobel Prize in Physics–have definitively shown that neutrinos have mass, but these experiments could only measure the difference in mass between the three different types of neutrinos known. The presence of neutrinos would affect the cosmic clustering on million-light-year scales, exactly the scales probed with the quasar spectra.

The new analysis suggests that the lightest neutrino mass has to be less than two times the previously measured mass difference. The new measurements also eliminate the possibility of an additional massive neutrino family suggested by some terrestrial experiments.

“Cosmology, the science of the very large, is able to tell us about properties of fundamental particles, such as neutrinos,” said Lam Hui of The U.S. Department of Energy’s Fermi National Accelerator Laboratory, who has been carrying out an independent analysis of these data, together with Scott Burles of MIT and others.

The new analysis also provides further support for the existence of dark energy, and suggests that dark energy is unchanging in time. This analysis provides the best limits on its time evolution to date.

“No evidence of dark energy changing in time has emerged so far, and the possibility that the universe will be torn apart by a big rip in the future is substantially reduced by these new results,” said Alexey Makarov of Princeton University, who also took part in this research.

Original Source: SDSS News Release

A major breakthrough in pinpointing some of the most primordial and violently star forming galaxies in the Universe has been made by a joint collaboration of UK and US astronomers using the Spitzer Space Telescope to resolve primordial galaxies initially detected by the James Clerk Maxwell telescope [JCMT]. UK astronomers from the University of Kent, The Royal Observatory Edinburgh and the University of Oxford teamed up with American cosmologists to finally identify these elusive galaxies. The work will be published in the Astrophysical Journal Supplement Spitzer Special Issue in September 2004.

Back in 1995, the UK’s SCUBA camera (Sub-millimetre Common User Bolometer Array) on the James Clerk Maxwell Telescope in Hawaii, which detects light with wavelengths just under a millimetre, began finding fuzzy traces of very distant, primordial galaxies. Some of these are either too distant or too dusty to be seen even by the Hubble Space Telescope. But SCUBA’s images on their own, and those of other similar cameras, are not fine enough: within the fuzzy SCUBA detections are sometimes many galaxies. So astronomers have spent enormous effort following up these SCUBA galaxies on other telescopes, particularly radio telescopes, to answer the question: which one is the primordial galaxy, and which ones are in the foreground? But even with the most sensitive radio telescope images ever made, only around half the SCUBA galaxies can be pinpointed unambiguously. Even worse, the radio telescopes miss all of the most distant and most primordial of SCUBA’s galaxies.

UK and US astronomers teamed up to combine Spitzer’s sharp images with SCUBA’s ability to find primordial galaxies. The team were stunned to find all the SCUBA galaxies in Spitzers field of view detected in only ten minutes with Spitzer. These breakthrough observations, described as a watershed by the team, finally give astronomers a way of unambiguously pinpointing even the most distant of SCUBA’s galaxies. This could only be done by combining SCUBA with the Spitzer Space Telescope: SCUBA shows there is a primordial, violent starburst somewhere in the vicinity, which is then pinpointed by Spitzer.

At the same time, Spitzer solved another mystery about SCUBA galaxies. When Galileo first trained a telescope at the Milky Way, he was astonished to find the fuzzy light resolved into many individual stars. This is, in essence, what the team of astronomers have done with the diffuse extragalactic background light seen from all directions at a wavelength of about half a millimetre. By comparing the distinct Spitzer galaxies with the SCUBA data, the team discovered that they had identified the sources of this cosmic background for the first time. This background is caused by an important population of galaxies: most of the stars in the early Universe are created in these galaxies, and star formation is where everything comes from – including the material that makes planets like our own. Finding where this star formation happens tells us, in a sense, where we came from. Identifying most of these galaxies is a second coup for the joint UK/US team.

Dr. Stephen Serjeant (University of Kent, UK) said, Our Spitzer Space Telescope images picked our galaxies out astonishingly quickly, in only ten minutes, when the community has been pouring effort into detecting them. This really is pioneering work and a great triumph for the Spitzer Space Telescope and the UKs SCUBA camera. To cap it all, at the same time weve found the galaxies that dominate the star formation in the early Universe. The Earth and everything on it is made from the dust created in stars like those people, trees, beef burgers, the lot.

Dr. Rob Ivison (Royal Observatory Edinburgh, UK) said, In 10 minutes, the Spitzer Space Telescope has managed to pinpoint the galaxies we have been chasing for 7 years. We can finally begin to sort the babies and teenagers of the galaxy world from the adults and senior citizens.

Dr. Herv Dole (University of Arizona USA and IAS, Orsay, France) said, These Spitzer observations were designed as the first joint survey using the MIPS and IRAC instruments on Spitzer, to assess the instrument sensitivities. As a matter of fact, it’s a great technological, operational and scientific success, overwhelming our wildest expectations. This demonstrates the amazing capabilities of Spitzer for studying galaxy evolution at high redshifts; no doubt that deeper and larger ongoing surveys will give even more exciting results!

Dr. Steve Willner (Harvard-Smithsonian Center for Astrophysics, USA) said, We expected to detect one or a few of these galaxies, but I was stunned that we detected all of the ones we looked at. The new data finally tell us what these galaxies are all about. We’ve known all along that they had to be far away and rapidly turning all their gas into stars, but now we know their true distances and ages.

Original Source: PPARC News Release

Astronomers using ESA?s X-ray observatory XMM-Newton have detected a small, bright ?hot spot? on the surface of the neutron star called Geminga, 500 light-years away. The hot spot is the size of a football field and is caused by the same mechanism producing Geminga?s X-ray tails. This discovery identifies the missing link between the X-ray and gamma-ray emission from Geminga.

Neutron stars are the smallest kind of stars known. They are the super-dense remnants of massive stars that died in cataclysmic explosions called supernovae. They have been thrown through space like cannonballs and set spinning at a furious rate, with magnetic fields hundreds of billions of times stronger than Earth?s.

In the case of Geminga, this cannonball contains one and a half times the mass of the Sun, squeezed into a sphere just 20 kilometres across and spinning four times every second.

A cloud bustling with electrically charged particles surrounds Geminga. These particles are shepherded by its magnetic and electric fields. ESA?s XMM-Newton observatory had already discovered that some of these particles are ejected into space, forming tails that stream behind the neutron star as it hurtles along.

Scientists did not know whether Geminga?s tails are formed by electrons or by their twin particles with an opposite electrical charge, called positrons. Nevertheless, they expected that, if for instance electrons are kicked into space, then the positrons should be funnelled down towards the neutron star itself, like in an ?own goal?. Where these particles strike the surface of the star, they ought to create a hot spot, a region considerably hotter than the surroundings.

An international team of astronomers, lead by Patrizia Caraveo, IASF-CNR, Italy, has now reported the detection of such a hot spot on Geminga using ESA?s XMM-Newton observatory.

With a temperature of about two million degrees, this hot spot is considerably hotter than the one half million degrees of the surrounding surface. According to this new work, Geminga?s hot spot is just 60 metres in radius.

“This hot spot is the size of a football field,” said Caraveo, “and is the smallest object ever detected outside of our Solar System.” Details of this size can presently be measured only on the Moon and Mars and, even then, only from a spacecraft in orbit around them.

The presence of a hot spot was suspected in the late 1990s but only now can we see it ?live?, emitting X-rays as Geminga rotates, thanks to the superior sensitivity of ESA?s X-ray observatory, XMM-Newton.

The team used the European Photon Imaging Cameras (EPIC) to conduct a study of Geminga, lasting about 28 consecutive hours and recording the arrival time and energy of every X-ray photon that Geminga emitted within XMM-Newton?s grasp.

“In total, this amounted to 76 850 X-ray counts ? twice as many as have been collected by all previous observations of Geminga, since the time of the Roman Empire,” said Caraveo.

Knowing the rotation rate of Geminga and the time of each photon?s arrival meant that astronomers could identify which photons were coming from each region of the neutron star as it rotates.

When they compared photons coming from different regions of the star, they found that the ?colour? of the X-rays, which corresponds to their energy, changed as Geminga rotated. In particular, they could clearly see a distinct colour change when the hot spot came into view and then disappeared behind the star.

This research closes the gap between the X-ray and gamma-ray emission from neutron stars. XMM-Newton has shown that they both can originate through the same physical mechanism, namely the acceleration of charged particles in the magnetosphere of these degenerate stars.

“XMM-Newton?s Geminga observation has been particularly fruitful,” said Norbert Schartel, ESA?s Project Scientist for XMM-Newton. “Last year, it yielded the discovery of the source tails and now it has found its rotating hot spot.”

Caraveo is already applying this new technique to other pulsating neutron stars observed by XMM-Newton looking for hot spots. This research represents an important new tool for understanding the physics of neutron stars.

Original Source: ESA News Release

Nearly five billion years ago, the giant gaseous planets Jupiter and Saturn formed, apparently in radically different ways.

So says a scientist at the University of California’s Los Alamos National Laboratory who created exhaustive computer models based on experiments in which the element hydrogen was shocked to pressures nearly as great as those found inside the two planets.

Working with a French colleague, Didier Saumon of Los Alamos’ Applied Physics Division created models establishing that heavy elements are concentrated in Saturn’s massive core, while those same elements are mixed throughout Jupiter, with very little or no central core at all. The study, published in this week’s Astrophysical Journal, showed that refractory elements such as iron, silicon, carbon, nitrogen and oxygen are concentrated in Saturn’s core, but are diffused in Jupiter, leading to a hypothesis that they were formed through different processes.

Saumon collected data from several recent shock compression experiments that have showed how hydrogen behaves at pressures a million times greater than atmospheric pressure, approaching those present in the gas giants. These experiments – performed over the past several years at U.S. national labs and in Russia – have for the first time permitted accurate measurements of the so-called equation of state of simple fluids, such as hydrogen, within the high-pressure and high-density realm where ionization occurs for deuterium, the isotope made of a hydrogen atom with an additional neutron.

Working with T. Guillot of the Observatoire de la Cote d’Azur, France, Saumon developed about 50,000 different models of the internal structures of the two giant gaseous planets that included every possible variation permitted by astrophysical observations and laboratory experiments.

“Some data from earlier planetary probes gave us indirect information about what takes place inside Saturn and Jupiter, and now we’re hoping to learn more from the Cassini mission that just arrived in Saturn’s orbit,” Saumon said. “We selected only the computer models that fit the planetary observations.”

Jupiter, Saturn and the other giant planets are made up of gases, like the sun: They are about 70 percent hydrogen by mass, with the rest mostly helium and small amounts of heavier elements. Therefore, their interior structures were hard to calculate because hydrogen’s equation of state at high pressures wasn’t well understood.

Saumon and Guillot constrained their computer models with data from the deuterium experiments, thereby reducing previous uncertainties for the equation of state of hydrogen, which is the central ingredient needed to improve models of the structures of the planets and how they formed.

“We tried to include every possible variation that might be allowed by the experimental data on shock compression of deuterium,” Saumon explained.

By estimating the total amount of the heavy elements and their distribution inside Jupiter and Saturn, the models provide a better picture of how the planets formed through the accretion of hydrogen, helium and solid elements from the nebula that swirled around the sun billions of years ago.

“There’s been general agreement that the cores of Saturn and Jupiter are different,” Saumon said. “What’s new here is how exhaustive these models are. We’ve managed to eliminate or quantify many of the uncertainties, so we have much better confidence in the range within which the actual data will fall for hydrogen, and therefore for the refractory metals and other elements.

“Although we can’t say our models are precise, we know quite well how imprecise they are,” he added.

These results from the models will help guide measurements to be taken by Cassini and future proposed interplanetary space probes to Jupiter.

Los Alamos National Laboratory is operated by the University of California for the National Nuclear Security Administration (NNSA) of the U.S. Department of Energy and works in partnership with NNSA’s Sandia and Lawrence Livermore national laboratories to support NNSA in its mission.

Los Alamos develops and applies science and technology to ensure the safety and reliability of the U.S. nuclear deterrent; reduce the threat of weapons of mass destruction, proliferation and terrorism; and solve national problems in defense, energy, environment and infrastructure.

Original Source: Los Alamos News Release

Today at the 13th Cambridge Workshop on “Cool Stars, Stellar Systems, and the Sun,” Dr. Kevin L. Luhman (Harvard-Smithsonian Center for Astrophysics) announced the discovery of a unique pair of newborn brown dwarfs in orbit around each other. Brown dwarfs are a relatively new class of objects discovered in the mid-1990s that are too small to ignite hydrogen fusion and shine as stars, yet too big to be considered planets. “Are brown dwarfs miniature failed stars, or super-sized planets, or are they altogether different from either stars or planets?” asks Luhman. The unique nature of this new brown dwarf pair has brought astronomers a step closer to the answer.

One possible explanation for the origin of brown dwarfs is that they are born in the same way as stars. Stars form in huge interstellar clouds in which gravity causes clumps of gas and dust to collapse into “seeds,” which then steadily pull in more and more material until they grow to become stars. However, when this process is studied in detail by computer, many simulations fail to produce brown dwarfs. Instead, all the seeds grow into full-fledged stars. This result led some astronomers to wonder if brown dwarfs and stars are created in different ways.

“In one alternative that has been proposed recently,” explains Luhman, “the seeds in an interstellar cloud pull on each other through their gravity, causing a slingshot effect and ejecting some of the seeds from the cloud before they have a chance to grow into stars. These small bodies are what we see as brown dwarfs, according to that hypothesis.”

Testing these ideas for the birth of brown dwarfs is hampered by the fact that brown dwarfs are normally extremely faint and hard to detect in the sky. For most of their lives, they are not hot enough to ignite hydrogen fusion, so they do not shine brightly like stars, and instead are relatively dim like planets. However, for a short time immediately following their birth, brown dwarfs are relatively bright due to the leftover heat from their formation. As a result, brown dwarfs are easiest to find and study at an age of around 1 million years, which is newborn compared to the 4.5 billion year age of our Sun.

Taking advantage of this fact, Luhman searched for newborn brown dwarfs in a cluster of young stars located 540 light-years away in the southern constellation of Chamaeleon. Luhman conducted his search using one of the two 6.5-meter-diameter Magellan telescopes at Las Campanas Observatory in Chile, which are among the largest telescopes in the world.

Of the two dozen new brown dwarfs found, most were isolated and floating in space by themselves. However, Luhman discovered one pair of brown dwarfs orbiting each other at a remarkably wide separation. All previously known pairs of brown dwarfs are relatively close to each other, less than half the distance of Pluto from the Sun. But the brown dwarfs in this new pair are much farther apart, about six times the distance of Pluto from the Sun.

Because these brown dwarfs are so far apart, they are very weakly bound to each other by gravity, and the slightest tug would permanently separate them. Therefore, Luhman concludes, “The mere existence of this extremely fragile pair indicates that these brown dwarfs were never subjected to the kind of violent gravitational pulls that they would undergo if they had formed as ejected seeds. Instead, it is likely that these baby brown dwarfs formed in the same way as stars, in a relatively gentle and undisturbed manner.”

Dr. Alan P. Boss (Carnegie Institution) agrees, stating, “Luhman’s discovery strengthens the case for the formation mechanism of brown dwarfs being similar to that of stars like the Sun, and hence for brown dwarfs being worthy of being termed ‘stars,’ even if they are too low in mass to be able to undergo sustained nuclear fusion.”

The discovery of this binary brown dwarf will be published in an upcoming issue of The Astrophysical Journal. The discovery paper currently is online in PDF format at http://cfa-www.harvard.edu/~kluhman/paper.pdf

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

The Magellan telescopes are operated by the Carnegie Institution of Washington, the University of Arizona, Harvard University, the University of Michigan, and the Massachusetts Institute of Technology.

Las Campanas Observatory is operated by the Carnegie Observatories, which was founded in 1904 by George Ellery Hale. It is one of six departments of the private, nonprofit Carnegie Institution of Washington, a pioneering force in basic scientific research since 1902.

Original Source: Harvard CfA News Release

Current theories of the formation of galaxies are based on the hierarchical merging of smaller entities into larger and larger structures, starting from about the size of a stellar globular cluster and ending with clusters of galaxies. According to this scenario, it is assumed that no massive galaxies existed in the young universe.

However, this view may now have to be revised. Using the multi-mode FORS2 instrument on the Very Large Telescope at Paranal, a team of Italian astronomers have identified four remote galaxies, several times more massive than the Milky Way galaxy, or as massive as the heaviest galaxies in the present-day universe. Those galaxies must have formed when the Universe was only about 2,000 million years old, that is some 12,000 million years ago.

The newly discovered objects may be members of a population of old massive galaxies undetected until now.

The existence of such systems shows that the build-up of massive elliptical galaxies was much faster in the early Universe than expected from current theory.

Hierarchical merging
Galaxies are like islands in the Universe, made of stars as well as dust and gas clouds. They come in different sizes and shapes. Astronomers generally distinguish between spiral galaxies – like our own Milky Way, NGC 1232 or the famous Andromeda galaxy – and elliptical galaxies, the latter mostly containing old stars and having very little dust or gas. Some galaxies are intermediate between spirals and ellipticals and are referred to as lenticular or spheroidal galaxies.

Galaxies are not only distinct in shape, they also vary in size: some may be as “light” as a stellar globular cluster in our Milky Way (i.e. they contain about the equivalent of a few million Suns) while others may be more massive than a million million Suns. Presently, more than half of the stars in the Universe are located in massive spheroidal galaxies.

One of the main open questions of modern astrophysics and cosmology is how and when galaxies formed and evolved starting from the primordial gas that filled the early Universe. In the most popular current theory, galaxies in the local Universe are the result of a relatively slow process where small and less massive galaxies merge to gradually build up bigger and more massive galaxies. In this scenario, dubbed “hierarchical merging”, the young Universe was populated by small galaxies with little mass, whereas the present Universe contains large, old and massive galaxies – the very last to form in the final stage of a slow assembling process.

If this scenario were true, then one should not be able to find massive elliptical galaxies in the young universe. Or, in other words, due to the finite speed of light, there should be no such massive galaxies very far from us. And indeed, until now no old elliptical galaxy was known beyond a radio-galaxy at redshift 1.55 that was discovered almost ten years ago.

The K20 survey
In order to better understand the formation process of galaxies and to verify if the hierarchical merging scenario is valid, a team of Italian and ESO astronomers used ESO’s Very Large Telescope as a “time machine” to do a search for very remote elliptical galaxies. However, this is not trivial. Distant elliptical galaxies, with their content of old and red stars, must be very faint objects indeed at optical wavelengths as the bulk of their light is redshifted into the infrared part of the spectrum. Remote elliptical galaxies are thus among the most difficult observational targets even for the largest telescopes; this is also why the 1.55 redshift record has persisted for so long.

But this challenge did not stop the researchers. They obtained deep optical spectroscopy with the multi-mode FORS2 instrument on the VLT for a sample of 546 faint objects found in a sky area of 52 arcmin2 (or about one tenth of the area of the Full Moon) known as the K20 field, and which partly overlaps with the GOODS-South area. Their perseverance paid off and they were rewarded by the discovery of four old, massive galaxies with redshifts between 1.6 and 1.9. These galaxies are seen when the Universe was only about 25% of its present age of 13,700 million years.

For one of the galaxies, the K20 team benefited also from the database of publicly available spectra in the GOODS-South area taken by the ESO/GOODS team.

A new population of galaxies
The newly discovered galaxies are thus seen when the Universe was about 3,500 million years old, i.e. 10,000 million years ago. But from the spectra taken, it appears that these galaxies contain stars with ages between 1,000 and 2,000 million years. This implies that the galaxies must have formed accordingly earlier, and that they must have essentially completed their assembly at a moment when the Universe was only 1,500 to 2,500 million years old.

The galaxies appear to have masses in excess of one hundred thousand million solar masses and they are therefore of sizes similar to the most massive galaxies in the present-day Universe. Complementary images taken within the GOODS (“The Great Observatories Origins Deep Survey”) survey by the Hubble Space Telescope show that these galaxies have structures and shapes more or less identical to those of the present-day massive elliptical galaxies.

The new observations have therefore revealed a new population of very old and massive galaxies.

The existence of such massive and old spheroidal galaxies in the early Universe shows that the assembly of the present-day massive elliptical galaxies started much earlier and was much faster than predicted by the hierarchical merging theory. Says Andrea Cimatti (INAF, Firenze, Italy), leader of the team: “Our new study now raises fundamental questions about our understanding and knowledge of the processes that regulated the genesis and the evolutionary history of the Universe and its structures.”

Original Source: ESO News Release

In the last few decades, scientists have discovered that there is a lot more to the universe than meets the eye: The cosmos appears to be filled with not just one, but two invisible constituents-dark matter and dark energy-whose existence has been proposed based solely on their gravitational effects on ordinary matter and energy.

Now, theoretical physicist Robert J. Scherrer has come up with a model that could cut the mystery in half by explaining dark matter and dark energy as two aspects of a single unknown force. His model is described in a paper titled “Purely Kinetic k Essence as Unified Dark Matter” published online by Physical Review Letters on June 30 and available online at http://arxiv.org/abs/astro-ph/0402316.

“One way to think of this is that the universe is filled with an invisible fluid that exerts pressure on ordinary matter and changes the way that the universe expands,” says Scherrer, a professor of physics at Vanderbilt University.

According to Scherrer, his model is extremely simple and avoids the major problems that have characterized previous efforts to unify dark matter and dark energy.

In the 1970s, astrophysicists postulated the existence of invisible particles called dark matter in order to explain the motion of galaxies. Based on these observations, they estimate that there must be about 10 times as much dark matter in the universe as ordinary matter. One possible explanation for dark matter is that it is made up of a new type of particle (dubbed Weakly Interacting Massive Particles, or WIMPs) that don’t emit light and barely interact with ordinary matter. A number of experiments are searching for evidence of these particles.

As if that weren’t enough, in the 1990s along came dark energy, which produces a repulsive force that appears to be ripping the universe apart. Scientists invoked dark energy to explain the surprise discovery that the rate at which the universe is expanding is not slowing, as most cosmologists had thought, but is accelerating instead. According to the latest estimates, dark energy makes up 75 percent of the universe and dark matter accounts for another 23 percent, leaving ordinary matter and energy with a distinctly minority role of only 2 percent.

Scherrer’s unifying idea is an exotic form of energy with well-defined but complicated properties called a scalar field. In this context, a field is a physical quantity possessing energy and pressure that is spread throughout space. Cosmologists first invoked scalar fields to explain cosmic inflation, a period shortly after the Big Bang when the universe appears to have undergone an episode of hyper-expansion, inflating billions upon billions of times in less than a second.

Specifically, Scherrer uses a second-generation scalar field, known as a k-essence, in his model. K-essence fields have been advanced by Paul Steinhardt at Princeton University and others as an explanation for dark energy, but Scherrer is the first to point out that one simple type of k-essence field can also produce the effects attributed to dark matter.

Scientists differentiate between dark matter and dark energy because they seem to behave differently. Dark matter appears to have mass and to form giant clumps. In fact, cosmologists calculate that the gravitational attraction of these clumps played a key role in causing ordinary matter to form galaxies. Dark energy, by contrast, appears to be without mass and spreads uniformly throughout space where it acts as a kind of anti-gravity, a repulsive force that is pushing the universe apart.

K-essence fields can change their behavior over time. When investigating a very simple type of k-essence field-one in which potential energy is a constant-Scherrer discovered that as the field evolves, it passes through a phase where it can clump and mimic the effect of invisible particles followed by a phase when it spreads uniformly throughout space and takes on the characteristics of dark energy.

“The model naturally evolves into a state where it looks like dark matter for a while and then it looks like dark energy,” Scherrer says. “When I realized this, I thought, ‘This is compelling, let’s see what we can do with it.'”

When he examined the model in more detail, Scherrer found that it avoids many of the problems that have plagued previous theories that attempt to unify dark matter and dark energy.

The earliest model for dark energy was made by modifying the general theory of relativity to include a term called the cosmological constant. This was a term that Einstein originally included to balance the force of gravity in order to form a static universe. But he cheerfully dropped the constant when astronomical observations of the day found it was not needed. Recent models reintroducing the cosmological constant do a good job of reproducing the effects of dark energy but do not explain dark matter.

One attempt to unify dark matter and dark energy, called the Chaplygin gas model, is based on work by a Russian physicist in the 1930s. It produces an initial dark matter-like stage followed by a dark energy-like evolution, but it has trouble explaining the process of galaxy formation.

Scherrer’s formulation has some similarities to a unified theory proposed earlier this year by Nima Arkani-Hamed at Harvard University and his colleagues, who attempt to explain dark matter and dark energy as arising from the behavior of an invisible and omnipresent fluid that they call a “ghost condensate.”

Although Scherrer’s model has a number of positive features, it also has some drawbacks. For one thing, it requires some extreme “fine-tuning” to work. The physicist also cautions that more study will be required to determine if the model’s behavior is consistent with other observations. In addition, it cannot answer the coincidence problem: Why we live at the only time in the history of the universe when the densities calculated for dark matter and dark energy are comparable. Scientists are suspicious of this because it suggests that there is something special about the present era.

Original Source: Vanderbilt University News Release