Category: Astronomy

Artist’s conception of a possible collision around BD +20 307. Image credit: Gemini Observatory/Jon Lomberg. Click to enlarge
A relatively young star located about 300 light-years away is greatly improving our understanding of the formation of Earth-like planets.

The star, going by the unassuming name of BD +20 307, is shrouded by the dustiest environment ever seen so close to a Sun-like star well after its formation. The warm dust is believed to be from recent collisions of rocky bodies at distances from the star comparable to that of the Earth from the Sun. The results were based on observations done at the Gemini and W.M. Keck Observatories, and were published in the July 21 issue of the British science journal Nature.

This finding supports the idea that comparable collisions of rocky bodies occurred early in our solar system’s formation about 4.5 billion years ago. Additionally, this work could lead to more discoveries of this sort which would indicate that the rocky planets and moons of our inner solar system are not as rare as some astronomers suspect.

?We were lucky. This set of observations is like finding the proverbial needle in the haystack,? said Inseok Song, the Gemini Observatory astronomer who led the U.S.-based research team. ?The dust we detected is exactly what we would expect from collisions of rocky asteroids or even planet-sized objects, and to find this dust so close to a star like our Sun bumps the significance way up. However, I can’t help but think that astronomers will now find more average stars where collisions like these have occurred.”

For years, astronomers have patiently studied hundreds of thousands of stars in the hopes of finding one with an infrared dust signature (the characteristics of the starlight absorbed, heated up and reemitted by the dust) as strong as this one at Earth-to-Sun distances from the star. “The amount of warm dust near BD+20 307 is so unprecedented I wouldn’t be surprised if it was the result of a massive collision between planet-size objects, for example, a collision like the one which many scientists believe formed Earth’s moon,” said Benjamin Zuckerman, UCLA professor of physics and astronomy, member of NASA’s Astrobiology Institute, and a co-author on the paper. The research team also included Eric Becklin of UCLA and Alycia Weinberger formerly at UCLA and now at the Carnegie Institution.

BD +20 307 is slightly more massive than our Sun and lies in the constellation Aries. The large dust disk that surrounds the star has been known since astronomers detected an excess of infrared radiation with the Infrared Astronomical Satellite (IRAS) in 1983. The Gemini and Keck observations provide a strong correlation between the observed emissions and dust particles of the size and temperatures expected by the collision of two or more rocky bodies close to a star.

Because the star is estimated to be about 300 million years old, any large planets that might orbit BD +20 307 must have already formed. However, the dynamics of rocky remnants from the planetary formantion process might be dictated by the planets in the system, as Jupiter did in our early solar system. The collisions responsible for the observed dust must have been between bodies at least as large as the largest asteroids present today in our solar system (about 300 kilometers across). “Whatever massive collision ocurred, it managed to totally pulverize a lot of rock,” said team member Alycia Weinberger.

Given the properties of this dust, the team estimates that the collisions could not have occurred more than about 1,000 years ago. A longer history would give the fine dust (about the size of cigarette smoke particles) enough time to be dragged into the central star.

The dusty environment around BD +20 307 is thought to be quite similar, but much more tenuous than what remains from the formation of our solar system. “What is so amazing is that the amount of dust around this star is approximately one million time greater than the dust around the Sun,” said UCLA team member Eric Becklin. In our solar system the remaining dust scatters sunlight to create an extremely faint glow called the zodiacal light (see image above). It can be seen under ideal conditions with the naked eye for a few hours after evening or before morning twilight.

The team?s observations were obtained using Michelle, a mid-infrared spectrograph/imager built by the UK Astronomy Technology Centre, on the Frederick C. Gillette Gemini North Telescope, and the Long Wavelength Spectrograph (LWS) at the W.M. Keck Observatory on Keck I.

Original Source: Gemini Observatory News Release

Artist?s conception of the gamma ray flare expanding from SGR 1806-20. Image credit: NASA.Click to enlarge
A gigantic explosion on a neutron star halfway across the Milky Way galaxy, the largest such explosion ever recorded in the universe, should allow astronomers for the first time to probe the interiors of these mysterious stellar objects.

An international team of astrophysicists, combing through data from a NASA X-ray satellite, the Rossi X-ray Timing Explorer, reports in the July 20th issue of Astrophysical Journal Letters that the explosion produced vibrations within the star, like a ringing bell, that generated rapid fluctuations in the X-ray radiation it emitted into space. These X-ray pulses, emitted during each seven second rotation by the fast-spinning star, contained the frequency vibrations of the neutron star?s massive quakes.

Much as geologists probe the Earth?s interior from seismic waves produced by earthquakes and solar astronomers study the sun using shock waves traveling through the sun, the X-ray fluctuations discovered from this explosion should provide critical information about the internal structure of neutron stars.

?This explosion was akin to hitting the neutron star with a gigantic hammer, causing it to ring like a bell,? said Richard Rothschild, an astrophysicist at the University of California?s Center for Astrophysics and Space Sciences and one of the authors of the journal report. ?Now the question is, What does the frequency of the neutron star?s oscillations?the tone produced by the ringing bell?mean?

?Does it mean neutron stars are just a bunch of neutrons packed together? Or do neutron stars have exotic particles, like quarks, at their centers as many scientists believe? And how does the crust of a neutron star float on top of its superfluid core? This is a rare opportunity for astrophysicists to study the interior of a neutron star, because we finally have some data theoreticians can chew on. Hopefully, they?ll be able to tell us what this all means.?

The biggest star quakes ripped through the neutron star at an incredible speed, vibrating the star at 94.5 cycles per second. ?This is near the frequency of the 22nd key of a piano, F sharp,? said Tomaso Belloni, an Italian member of the team who measured the signals.

The international team?led by GianLuca Israel, Luigi Stella and Belloni of Italy?s National Institute of Astrophysics?discovered the oscillations from data it retrieved two days after Christmas by the Rossi X-Ray Timing Explorer, a satellite designed to study the fluctuating X-ray emissions from stellar sources. The peculiar oscillations the researchers found began three minutes after a titanic explosion on a neutron star that, for only a tenth of a second, released more energy than the sun emits in 150,000 years. The oscillations then gradually receded after about 10 minutes.

Neutron stars are the dense, rapidly spinning cores of matter that result from the crushing collapse of a star that has depleted all of its nuclear fuel and exploded in a cataclysmic event known as a supernova. The collapse is so crushing that electrons are forced into the atomic nucleus and combine with protons to become neutrons. The resulting sphere of neutrons is so dense?packing the mass of the sun in a sphere only 10 miles in diameter?that a spoonful of its matter would weigh billions of tons on Earth.

Most of the millions of neutron stars in our Milky Way galaxy produce magnetic fields that are a trillion times stronger than those of the Earth. But astrophysicists have discovered less than a dozen ultra-high magnetic neutron stars, called ?magnetars,? with magnetic fields a thousand times greater?strong enough to strip information from a credit card at a distance halfway to the moon.

These intense magnetic fields are strong enough they sometimes buckle the crust of neutron stars, causing ?star quakes? that result in the release of gamma rays, a more energetic form of radiation than X-rays. Four of these magnetars are known to do just that and are termed ?soft gamma repeaters,? or SGRS, by astrophysicists because they flare up randomly and release a series of brief bursts of gamma rays.

SGR 1806-20, the formal designation of the neutron star that exploded and sent X-rays flooding through the galaxy on December 27, 2004?producing a flash brighter than anything ever detected beyond the solar system?is one of them. The flash was so bright that it blinded all X-ray satellites in space for an instant and lit up the Earth?s upper atmosphere.

Astrophysicists suspect the burst of gamma-ray and X-ray radiation from this unusually large explosion could have come from a highly twisted magnetic field surrounding the neutron star that suddenly snapped, creating a titanic quake on the neutron star.

?The scenario was probably analogous to a twisted rubber band that finally broke and in the process released a tremendous amount of energy,? said Rothschild. ?With this energy release, the magnetic field surrounding the magnetar was presumably able to relax to a more stable configuration.?

The December 27 flash of energy was detected by several other NASA and European satellites and recorded by radio telescopes around the world. It already has been the subject of numerous scientific papers published in recent months.

?The sudden and surprising occurrence of this giant flare, which will help us learn more about the nature of magnetars and the internal make-up of neutron stars,? said Rothschild, ?underlines the importance of having satellites and telescopes with the capacity to record unusual and unpredictable phenomena in the universe.?

Other members of the international team were Pier Giorgio Casella, Simone Dall?Osso and Massimo Persic of Italy?s National Institute of Astrophysics; Yoel Rephaeli of UCSD and the University of Tel Aviv; Duane Gruber, formerly of UCSD and now at the Eureka Scientific Corporation in Oakland, Calif; and Nanda Rea of the National Institute for Space Research in the Netherlands.

Original Source: UCSD News Release

Here’s a link to the biggest stars in the Universe.

An artist’s impression of a Superwind in a young massive galaxy. Image credit: PPARC/David Hardy. Click to enlarge
A team of astronomers, led by the University of Durham, has discovered the aftermath of a spectacular explosion in a galaxy 11.5 billion light years away. Their observations, reported today (14th July 2005) in the journal Nature provide the most direct evidence yet of a galaxy being almost torn apart by explosions that produce a stream of high-speed material known as “Superwinds”. The observations were made using the 4.2 metre William Herschel Telescope on La Palma in which the UK is a major stakeholder.

Through Superwinds, galaxies are thought to blast a significant part of their gas into intergalactic space at speeds of up to several hundred miles per second. The driving force behind them is the explosion of many massive stars during an intense burst of star formation early in the galaxy’s life, possibly assisted by energy from a super massive black hole growing at its heart.

Superwinds are vital to the theory of galaxy formation for several reasons: firstly, they limit the sizes of galaxies by preventing further star formation – without them theoretical models indicate far more very bright galaxies than are actually seen in the Universe today. Secondly, they carry heavy elements – Star dust – far from their production sites in stars out into intergalactic space, providing raw material for planets and life across the Universe. Whilst the theories predicted Superwinds of this kind existed, previously observed examples were much smaller phenomena in nearby galaxies. These observations provide some of the most direct evidence yet for the existence of large-scale, galaxy-wide superwinds so far back in the history of the Universe.

The discovery of the Superwind was made by observing the gas in the halo of a galaxy (known as “LAB-2”), which at over 300,000 light years across is about three times larger than the disk of our own Milky Way galaxy. The astronomers discovered that light from hot glowing hydrogen gas is dimmed in a very specific way across the entire galaxy.

“We believe that the dimming is caused by a shell of cooled material which has been swept-up from the surroundings by a galaxy-wide Superwind explosion,” said Dr. Richard Wilman of the University of Durham. “Based on the uniformity of the absorption across the galaxy, it appears that the explosion was triggered several hundred million years earlier. This allows time for the gas to cool and to slow down from its high ejection speed, and thus to produce the absorption. As we see it, the shell is probably a few hundred thousand light years in front of its parent galaxy,” added Dr. Wilman.

Astronomers have long been puzzled about why key elements for the formation of planets and ultimately life (such as carbon, oxygen and iron) are so widely distributed throughout the Universe; only 2 billion years after the Big Bang, the remotest regions of intergalactic space have been enriched with them. The Superwind observed in this galaxy shows how such blast waves can travel through space carrying the elements formed deep within galaxies.

Crucial to the discovery and its interpretation was the ability to obtain detailed information on the gas in two-dimensions across the whole galaxy. This was made possible by a technique known as integral field spectroscopy, which is only just reaching maturity on the world’s largest telescopes.

Dr Joris Gerssen, a key member of the Durham team, explains, “Most astronomical spectroscopy is performed by placing a small aperture, or a narrow slit on the target, which for complex, extended sources such as this galaxy gives a rather incomplete picture”.

To overcome this the astronomers used an integral field spectrograph called ‘Sauron’ for a large survey of nearby galaxies, built at the Observatoire de Lyon by a collaboration of French, Dutch and UK astronomers.

Dr Gerssen added,” “Sauron is truly unique and its high efficiency means that it can more than hold its own against instruments on the world’s largest telescopes, some twice the size of the William Herschel Telescope. Nevertheless, the sheer distance of our target galaxy meant that Sauron had to stare at it for over 15 hours in order to make this discovery”.

“Sauron has provided us with the best evidence so far for an extensive outflow from a galaxy undergoing a huge starburst. These measurements are among the first steps towards understanding the physics of galaxy formation.,” commented Prof. Roger Davies, University of Oxford, one of the institutes involved on Sauron,” and we look forward to using similar two-dimensional spectrographs being built for 8m telescopes; these will probe the galaxy formation process to even earlier times.”

To date, observational evidence for Superwinds in young galaxies in the distant Universe has been largely indirect and circumstantial; efforts have focussed on searching for their subtle statistical signatures in large surveys of galaxies and intergalactic gas.

According to Prof. Richard Bower, from the University of Durham’s Institute of Computational Cosmology who initiated the research, “Astronomers have observed high-speed outflows in distant star-forming galaxies for several years, but never before have we been able to gauge their true scale from observations of a single galaxy. By taking advantage of the highly extended emission source of this galaxy, we can see the outflow as a kind of silhouette against the whole galaxy. This suggests that Superwinds are truly galaxy-wide in scale, and that they really are as important as our theories require.”

Original Source: PPARC News Release

Artist’s impression of neutron star IGR J16283-4838. Image Credit:NASA/Dana Berry. Click to enlarge
An international team of scientists has uncovered a rare type of neutron star so elusive that it took three satellites to identify it.

The findings, made with ESA?s Integral satellite and two NASA satellites, reveals new insights about star birth and death in our Galaxy. We report this discovery, highlighting the complementary nature of European and US spacecraft, on the day in which ESA?s Integral celebrates 1000 days in orbit.
The neutron star, called IGR J16283-4838, is an ultra-dense ?ember? of an exploded star and was first seen by Integral on 7 April 2005. This neutron star is about 20,000 light years away, in a ?double hiding place?. This means it is deep inside the spiral arm Norma of our Milky Way galaxy, obscured by dust, and then buried in a two-star system enshrouded by dense gas.

?We are always hunting for new sources,? said Simona Soldi, the scientist at the Integral Science Data Centre in Geneva, Switzerland, who first saw the neutron star. ?It is exciting to find something so elusive. How many more sources like this are out there??

Neutron stars are the core remains of ?supernovae?, exploded stars once about ten times as massive as our Sun. They contain about a Sun’s worth of mass compacted into a sphere about 20 kilometres across.

?Our Galaxy?s spiral arms are loaded with neutron stars, black holes and other exotic objects, but the problem is that the spiral arms are too dusty to see through,? said Dr Volker Beckmann at NASA Goddard Spaceflight Centre, lead author of the combined results.

?The right combination of X-ray and gamma-ray telescopes could reveal what is hiding there, and provide new clues about the true star formation rate in our Galaxy,? he added.

Because gamma rays are hard to focus into sharp images, the science team then used the X-ray telescope on Swift to determine a precise location. In mid April 2005, Swift confirmed that the light was ?highly absorbed?, which means the binary system was filled with dense gas from the stellar wind of the companion star.

Later the scientists used the Rossi Explorer to observe the source as it faded away. This observation revealed a familiar light signature, clinching the case for a fading high-mass X-ray binary with a neutron star.

IGR J16283-4838 is the seventh so-called ?highly absorbed?, or hidden neutron star to be identified. Neutron stars, created from fast-burning massive stars, are intrinsically tied to star formation rates. They are also energetic ?beacons? in regions too dusty to study in detail otherwise. As more and more are discovered, new insights about what is happening in the Galaxy’s spiral arms begin to emerge.

IGR J16283-4838 revealed itself with an ?outburst? on or near its surface. Neutron stars such as IGR J16283-4838 are often part of binary systems, orbiting a normal star. Occasionally, gas from the normal star, lured by gravity, crashes onto the surface of the neutron star and releases a great amount of energy. These outbursts can last for weeks before the system returns to dormancy for months or years.

Integral, the Rossi Explorer and Swift all detect X-rays and gamma rays, which are far more energetic than the visible light that our eyes detect. Yet each satellite has different capabilities. Integral has a large field of view, enabling it to scan our Milky Way galaxy for neutron stars and black hole activity.

Swift contains a high-resolution X-ray telescope, which allowed scientists to zoom in on IGR J16283-4838. The Rossi Explorer has a timing spectrometer, a device used to uncover properties of the light source, such as speed and rapid variations in the order of milliseconds.

Original Source: ESA Portal

This view of nearly 10,000 galaxies is the deepest visible-light image of the cosmos. Image credit: Hubble. Click to enlarge
One of the fastest supercomputers in the world and the first ever designed specifically to study the evolution of star clusters and galaxies is now in operation at Rochester Institute of Technology.

The new computer, built by David Merritt, professor of physics in RIT?s College of Science, uses a novel architecture to reach speeds much higher than that of standard supercomputers of comparable size.

Known as gravitySimulator, the computer is designed to solve the ?gravitational N-body problem?. It simulates how a galaxy evolves as the stars move about each other in response to their own gravity. This problem is computationally demanding because there are so many interactions to calculate requiring a tremendous amount of computer time. As a result, standard supercomputers can only carry out such calculations with thousands of stars at a time.

The new computer achieves much greater performance by incorporating special accelerator boards, called GRAPEs or Gravity Pipelines, into a standard Beowulf-like cluster. The gravitySimulator, which is one of only two machines of its kind in the world, achieves a top speed of 4 Teraflops, or four trillion calculations per second, making it one of the 100 fastest computers in the world, and it can handle up to 4 million stars at once. The computer cost over $500,000 to construct and was funded by RIT, the National Science Foundation, and NASA.

Since gravitySimulator was installed in the spring, Merritt and his associates have been using it to study the binary black hole problem- what happens when two galaxies collide and their central, supermassive black holes form a bound pair.

?Eventually the two black holes are expected to merge into a single, larger black hole,? Merritt says. ?But before that happens, they interact with the stars around them, ejecting some and swallowing others. We think we see the imprints of this process in nearby galaxies, but so far no one has carried out simulations with high enough precision to test the theory.?

Merritt and his team will also use gravitySimulator to study the dynamics of the central Milky Way Galaxy in order to understand the origin of our own black hole.

Merritt sees the gravitySimulator as an important example of RIT?s development as a major scientific research institute. ?Our unique combination of in-class instruction, experiential learning and research will be a major asset in the continued development of astrophysics and other research disciplines here at RIT,? Merritt says. ?The gravitySimulator is the perfect example of the cutting edge work we are already doing and will be a major stepping stone for the development of future scientific research.?

Original Source: RIT News Release

Computer illustration of microquasar LS5039. Image credit: PPARC. Click to enlarge.
In a recent issue of Science Magazine, the High Energy Stereoscopic System (H.E.S.S.) team of international astrophysicists reports the discovery of another new type of very high energy (VHE) gamma ray source.

Gamma-rays are produced in extreme cosmic particle accelerators such as supernova explosions and provide a unique view of the high energy processes at work in the Milky Way. VHE gamma-ray astronomy is still a young field and H.E.S.S. is conducting the first sensitive survey at this energy range, finding previously unknown sources.

The object that is producing the high energy radiation is thought to be a ‘microquasar’. These objects consist of two stars in orbit around each other. One star is an ordinary star, but the other has used up all its nuclear fuel, leaving behind a compact corpse. Depending on the mass of the star that produced it, this compact object is either a neutron star or a black hole, but either way its strong gravitational pull draws in matter from its companion star. This matter spirals down towards the neutron star or the black hole, in a similar way to water spiraling down a plughole.

However, sometimes the compact object receives more matter than it can cope with. The material is then squirted away from the system in a jet of matter moving at speeds close to that of light, resulting in a microquasar. Only a few such objects are known to exist in our galaxy and one of them, an object called LS5039, has now been detected by the H.E.S.S. team.

In fact, the real nature LS5039 is something of a mystery. It is not clear what the compact object is. Some of the characteristics suggest it is a neutron star, some that it is a black hole. Not only that, but the jet isn’t much of a jet; although it is moving at about 20% of the speed of light, which might seem a lot, in the context of these objects it’s actually quite slow.

Nor is it clear how the gamma rays are being produced. As Dr. Guillaume Dubus of the Ecole Polytechnique points out “We really shouldn’t have detected this object. Very high energy gamma rays emitted close to the companion star are more likely to be absorbed, creating a matter/antimatter cascade, than escape from the system.”

Dr Paula Chadwick of the University of Durham adds “It’s very exciting to have added another class of object to the growing catalogue of gamma ray sources. It’s an intriguing object – it will take more observations to work out what is going on in there.”

The H.E.S.S. array is ideal for finding new VHE gamma ray objects; because it’s wide field of view (ten times the diameter of the Moon) means that it can survey the sky and discover previously unknown sources.

The results were obtained using the High Energy Stereoscopic System (H.E.S.S.) telescopes in Namibia, in South-West Africa. This system of four 13 m diameter telescopes is currently the most sensitive detector of VHE gamma-rays – radiation that is a million, million times more energetic than the visible light. These high energy gamma rays are quite rare even for relatively strong sources; only about one gamma ray per month hits a square metre at the top of the Earth’s atmosphere. Also, since they are absorbed in the atmosphere, a direct detection of a significant number of the rare gamma rays would require a satellite of huge size. The H.E.S.S. telescopes employ a trick – they use the atmosphere as detector medium. When gamma rays are absorbed in the air, they emit short flashes of blue light, named Cherenkov light, lasting a few billionths of a second. This light is collected by the H.E.S.S. telescopes with large mirrors and extremely sensitive cameras and can be used to create images of astronomical objects as they appear in gamma-rays.

The H.E.S.S. telescopes represent several years of construction effort by an international team of more than 100 scientists and engineers from Germany, France, the UK, Ireland, the Czech Republic, Armenia, South Africa and the host country Namibia. The instrument was inaugurated in September 2004 by the Namibian Prime Minister, Theo-Ben Guirab, and its first data have already resulted in a number of important discoveries, including the first astronomical image of a supernova shock wave at the highest gamma-ray energies.

Original Source: PPARC News Release

One of the meteorites analyzed to help pinpoint the age of Milky Way. Image credit: Nicolas Dauphas, University of Chicago. Click to enlarge.
The University of Chicago?s Nicolas Dauphas has developed a new way to calculate the age of the Milky Way that is free of the unvalidated assumptions that have plagued previous methods. Dauphas? method, which he reports in the June 29 issue of the journal Nature, can now be used to tackle other mysteries of the cosmos that have remained unsolved for decades.

?Age determinations are crucial to a fundamental understanding of the universe,? said Thomas Rauscher, an assistant professor of physics and astronomy at the University of Basel in Switzerland. ?The wide range of implications is what makes Nicolas? work so exciting and important.?

Dauphas, an Assistant Professor in Geophysical Sciences, operates the Origins Laboratory at the University of Chicago. His wide-ranging interests include the origins of Earth?s atmosphere, the oldest rocks that may contain evidence for life on Earth and what meteorites reveal about the formation of the solar system.

In his latest work, Dauphas has honed the accuracy of the cosmic clock by comparing the decay of two long-lived radioactive elements, uranium-238 and thorium-232. According to Dauphas? new method, the age of the Milky Way is approximately 14.5 billion years, plus or minus more than 2 billion years.

That age generally agrees with the estimate of 12.2 billion years?nearly as old as the universe itself? as determined by previously existing methods. Dauphas? finding verifies what was already suspected, despite the drawbacks of existing methods: ?After the big bang, it did not take much time for large structures to form, including our Milky Way galaxy,? he said.

The age of 12 billion years for the galaxy relied on the characteristics of two different sets of stars, globular clusters and white dwarfs. But this estimate depends on assumptions about stellar evolution and nuclear physics that scientists have yet to substantiate to their complete satisfaction.

Globular clusters are clusters of stars that exist on the outskirts of a galaxy. The processes of stellar evolution suggested that most of the stars in globular clusters are nearly as old as the galaxy itself. When the big bang occurred 13.7 billion years ago, the only elements in the universe were hydrogen, helium and a small quantity of lithium. The Milky Way?s globular clusters have to be nearly that old because they contain mostly hydrogen and helium. Younger stars contain heavier elements that were recycled from the remains of older stars, which initially forged these heavier elements in their cores via nuclear fusion.

White dwarf stars, meanwhile, are stars that have used up their fuel and have advanced to the last stage of their lives. ?The white dwarf has no source of energy, so it just cools down. If you look at its temperature and you know how fast it cools, then you can approximate the age of the galaxy, because some of these white dwarfs are about as old as the galaxy,? Dauphas said.

A more direct way to calculate the age of stars and the Milky Way depends on the accuracy of the uranium/thorium clock. Scientists can telescopically detect the optical ?fingerprints? of the chemical elements. Using this capability, they have measured the uranium/thorium ratio in a single old star that resides in the halo of the Milky Way.

Original Source: University of Chicago News Release

The white dwarf star Gliese 86B is the tiny dot to the left of the bright star. Image credit: ESO. Click to enlarge.
The team has found that a star known as Gliese 86 – part of the southern constellation Erinadus, and just visible to the unaided eye – has another companion in addition to the gas giant planet that was found in a tight orbit around it seven years ago. However, this more distant companion is not another planet, but a white dwarf star that is about as far from Gliese 86 as is Uranus from the sun. The discovery marks the first time a planet has been found in the vicinity of a white dwarf, and could have implications for our own solar system – which will itself be centered around a white dwarf in a few billion years.

“This is the first observational evidence that planets can survive the white dwarf formation process of a star several astronomical units away,” said researcher team member Markus Mugrauer, a doctoral student at the Astrophysical Institute and University Observatory, University of Jena, Germany. “In theory, nearby planets should not survive the formation process, but this finding is evidence that, if they are sufficiently distant, they can. This is of interest because most stars in the galaxy, including our own, will eventually evolve into white dwarfs.”

The study, which Mugrauer conducted with Dr. Ralph Neuhaeuser, director of observations at the university’s astrophysics institute, were published as a letter in the May issue of “Monthly Notices of the Royal Astronomical Society.”

The planet itself was discovered in late 1998 at Switzerland’s La Silla observatory, and was the first exoplanet to be found using a telescope at La Silla that had been fitted with a spectrograph for the express purpose of searching for planets around other stars. Further analysis of Gliese 86’s movements indicated that the star also had a faint stellar companion that had not yet been observed, possibly a brown dwarf — an object with insufficient mass to sustain fusion in its core.

“No one was sure what it was, however,” Mugrauer said. “Just as the planet itself had been found by its influence on Gliese 86 but had not actually been ‘seen,’ the companion was tugging on the star but it was difficult to separate from background light.”

To resolve Gliese 86’s companion, the pair used high contrast observations using the 8m Very Large Telescope at La Silla together with a new simultaneous differential imaging device.

“With these instruments, we can resolve objects about 150,000 times fainter than the central star, but which are still very close to them,” Mugrauer said. “This allows us to search for close and very faint companions of our target stars.”

After filtering out the background noise, they found Gliese’s companion orbiting at a distance of about 21 AU, but were surprised to find it hotter than expected — at least 3700 Kelvin, too warm to be a brown dwarf. Judging by its velocity and distance from Gliese 86, they also found that the white dwarf has about 55 percent the mass of our sun, making it smaller than Gliese 86, which has 70 percent of our sun’s mass.

“But since a star loses a good deal of its mass as it evolves into a white dwarf, this companion was once much larger than Gliese 86, perhaps as large as our own sun or even larger,” Mugrauer said. “It was much closer to Gliese 86 before it became a white dwarf, perhaps 15 AU, or a distance about halfway between the orbits of Saturn and Uranus in our own system. It migrated outward after it lost mass during its evolution into a white dwarf.”

Because of the planet’s size and distance from the red giant, Mugrauer said, the companion’s evolution wouldn’t have dramatically affected the planet’s size.

“The planet’s gravity is simply too strong to lose mass because of the impacting material and due to its large separation,” he said. “However, during the red giant phase, the companion would have swollen up and become 10,000 more luminous. It would also have become the dominant heat source of the planet, heating it 1000K or more.”

Nowadays, he said, the companion would probably appear as a very bright star in the planet’s night sky, but would provide it with very little additional heat in comparison with Gliese 86, which the giant planet circles at about a tenth the distance of the Earth to the sun.

“We expect that distant planets — those farther than Jupiter is from our sun — can survive the evolution of a star from red giant to white dwarf. These observations tend to confirm that expectation,” Mugrauer said. “In the Gliese 86 system in particular, the separation between the white dwarf and the exoplanet is large enough that it seems very possible that a planet can survive the red giant phase of a G dwarf such as our sun.”

But Mugrauer said that he and Neuhaeuser would continue to search for companion stars in this and other exoplanetary systems because, despite the number of planets that have been found circling other stars, little is known about the properties of planets in binary systems. Planets in close binaries, like Gliese 86, are rare. “Gliese 86 is one of the closest binary systems hosting a planet,” Mugrauer said.

“These systems provide important information about the planet formation process and how the multiplicity of the host star may effect it,” he said. “Gliese 86 is only about 35 light years from earth, so it was near the top of our list of stars to explore. But we are on our way to checking out a lot more.”

Written by Chad Boutin

Artist illustratino of a planetary zone filled with pebbles. Image credit: CfA. Click to enlarge.
Interstellar travelers might want to detour around the star system TW Hydrae to avoid a messy planetary construction site. Astronomer David Wilner of the Harvard-Smithsonian Center for Astrophysics (CfA) and his colleagues have discovered that the gaseous protoplanetary disk surrounding TW Hydrae holds vast swaths of pebbles extending outward for at least 1 billion miles. These rocky chunks should continue to grow in size as they collide and stick together until they eventually form planets.

“We’re seeing planet building happening right before our eyes,” said Wilner. “The foundation has been laid and now the building materials are coming together to make a new solar system.”

Wilner used the National Science Foundation’s Very Large Array to measure radio emissions from TW Hydrae. He detected radiation from a cold, extended dust disk suffused with centimeter-sized pebbles. Such pebbles are a prerequisite for planet formation, created as dust collects together into larger and larger clumps. Over millions of years, those clumps grow into planets.

“We’re seeing an important step on the path from interstellar dust particles to planets,” said Mark Claussen (NRAO), a co-author on the paper announcing the discovery. “No one has seen this before.”

A dusty disk like that in TW Hydrae tends to emit radio waves with wavelengths similar to the size of the particles in the disk. Other effects can mask this, however. In TW Hydrae, the astronomers explained, both the relatively close distance of the system and the stage of the young star’s evolution are just right to allow the relationship of particle size and wavelength to prevail. The scientists observed the young star’s disk with the VLA at several centimeter-range wavelengths. “The strong emission at wavelengths of a few centimeters is convincing evidence that particles of about the same size are present,” Claussen said.

Not only does TW Hydrae show evidence of ongoing planet formation, it also shows signs that at least one giant planet may have formed already. Wilner’s colleague, Nuria Calvet (CfA), has created a computer simulation of the disk around TW Hydrae using previously published infrared observations. She showed that a gap extends from the star out to a distance of about 400 million miles – similar to the distance to the asteroid belt in our solar system. The gap likely formed when a giant planet sucked up all the nearby material, leaving a hole in the middle of the disk.

Located about 180 light-years away in the constellation Hydra the Water Snake, TW Hydrae consists of a 10 million-year-old star about four-fifths as massive as the Sun. The protoplanetary disk surrounding TW Hydrae contains about one-tenth as much material as the Sun – more than enough to form one or more Jupiter-sized worlds.

“TW Hydrae is unique,” said Wilner. “It’s nearby, and it’s just the right age to be forming planets. We’ll be studying it for decades to come.”

This research was published in the June 20, 2005, issue of The Astrophysical Journal Letters.

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.

Original Source: Harvard CfA News Release

Simulation of interstellar grains of dust. Image credit: OSU. Click to enlarge.
Science fiction writer Harlan Ellison once said that the most common elements in the universe are hydrogen and stupidity.

While the verdict is still out on the volume of stupidity, scientists have long known that hydrogen is indeed by far the most abundant element in the universe. When they peer through their telescopes, they see hydrogen in the vast clouds of dust and gas between stars ?- especially in the denser regions that are collapsing to form new stars and planets.

But one mystery has remained: why is much of that hydrogen in molecular form ?- with two hydrogen atoms bonded together ?- rather than its single atomic form? Where did all that molecular hydrogen come from? Ohio State University researchers recently decided to try to figure it out.

They discovered that one seemingly tiny detail — whether the surfaces of interstellar dust grains are smooth or bumpy — could explain why there is so much molecular hydrogen in the universe. They reported their results at the 60th International Symposium on Molecular Spectroscopy, held at Ohio State University .

Hydrogen is the simplest atomic element known; it consists of just one proton and one electron. Scientists have always taken for granted the existence of molecular hydrogen when forming theories about where all the larger and more elaborate molecules in the universe came from. But nobody could explain how so many hydrogen atoms were able to form molecules — until now.
When it comes to making molecular hydrogen, the ideal microscopic host surface is ?less like the flatness of Ohio and more like a Manhattan skyline.?

For two hydrogen atoms to have enough energy to bond in the cold reaches of space, they first have to meet on a surface, explained Eric Herbst, Distinguished University Professor of physics at Ohio State.

Though scientists suspected that space dust provided the necessary surface for such chemical reactions, laboratory simulations of the process never worked. At least, they didn’t work well enough to explain the full abundance of molecular hydrogen that scientists see in space.

Herbst, professor of physics, chemistry, and astronomy, joined with Herma Cuppen, a postdoctoral researcher, and Qiang Chang, a doctoral student, both in physics, to simulate different dust surfaces on a computer. They then modeled the motion of two hydrogen atoms tumbling along the different surfaces until they found one another to form a molecule.

Given the amount of dust that scientists think is floating in space, the Ohio State researchers were able to simulate the creation of the right amount of hydrogen, but only on bumpy surfaces.

When it comes to making molecular hydrogen, the ideal microscopic host surface is ?less like the flatness of Ohio and more like a Manhattan skyline,? Herbst said.

The problem with past simulations, it seems, is that they always assumed a flat surface.

Cuppen understands why. ?When you want to test something, starting with a flat surface is just faster and easier,? she said

She should know. She’s an expert in surface science, yet it still took her months to assemble the bumpy dust model, and she’s still working to refine it. Eventually, other scientists will be able to use the model to simulate other chemical reactions in space.

In the meantime, the Ohio State scientists are collaborating with colleagues at other institutions who are producing and using actual bumpy surfaces that mimic the texture of space dust. Though real space dust particles are as small as grains of sand, these larger, dime-sized surfaces will enable scientists to test whether different textures help molecular hydrogen to form in the lab.

Original Source: OSU News Release