Category: Astronomy

Artist illustraton of a black hole consuming a neutron star. Image credit: Dana Berry/NASA. Click to enlarge.
Scientists have solved a 35-year-old mystery of the origin of powerful, split-second flashes of light called short gamma-ray bursts. These flashes, brighter than a billion suns yet lasting only a few milliseconds, have been simply too fast to catch… until now.

If you guessed that a black hole is involved, you are at least half right. Short gamma-ray bursts arise from collisions between a black hole and a neutron star or between two neutron stars. In the first scenario, the black hole gulps down the neutron star and grows bigger. In the second scenario, the two neutron stars create a black hole.

Gamma-ray bursts, the most powerful explosions known, were first detected in the late 1960s. They are random, fleeting, and can occur from any region of the sky. Try finding the location of a camera flash somewhere in a vast sports stadium and you’ll have a sense of the challenge facing gamma-ray burst hunters. Solving this mystery took unprecedented coordination among scientists using a multitude of ground-based telescopes and NASA satellites.

Two years ago scientists discovered that longer bursts, lasting over two seconds, arise from the explosion of very massive stars. About 30 percent of bursts, however, are short and under two seconds.

Four short gamma-ray bursts have been detected since May. Two of these are featured in four papers in the October 6 issue of Nature. One burst from July provides the “smoking gun” evidence to support the collision theory. Another burst goes a step further by providing tantalizing, first-time evidence of a black hole eating a neutron star—first stretching the neutron star into a crescent, swallowing it, and then gulping up crumbs of the broken star in the minutes and hours that followed.

These discoveries might also aid in the direct detection of gravitational waves, never before seen. Such mergers create gravitational waves, or ripples in spacetime. Short gamma-ray bursts could tell scientists when and where to look for the ripples.

“Gamma-ray bursts in general are notoriously difficult to study, but the shortest ones have been next to impossible to pin down,” said Dr. Neil Gehrels of NASA Goddard Space Flight Center in Greenbelt, Md., principal investigator of NASA’s Swift satellite and lead author on one of the Nature reports. “All that has changed. We now have the tools in place to study these events.”

The Swift satellite detected a short burst on May 9, and NASA’s High-Energy Transient Explorer (HETE) detected another on July 9. These are the two bursts featured in Nature. Swift and HETE quickly and autonomously relayed the burst coordinates to scientists and observatories via cell phone, beepers and e-mail.

The May 9 event marked the first time scientists identified an afterglow for a short gamma-ray burst, something commonly seen after long bursts. That discovery was the subject of a May 11 NASA press release. The new results published in Nature represent thorough analyses of these two burst afterglows, which clinch the case for the origin of short bursts.

“We had a hunch that short gamma-ray bursts came from a neutron star crashing into a black hole or another neutron star, but these new detections leave no doubt,” said Dr. Derek Fox of Penn State, lead author on one Nature report detailing a multi-wavelength observation.

Fox’s team discovered the X-ray afterglow of the July 9 burst with NASA’s Chandra X-ray Observatory. A team led by Prof. Jens Hjorth of the University of Copenhagen then identified the optical afterglow using the Danish 1.5-meter telescope at the La Silla Observatory in Chile. Fox’s team then continued its studies of the afterglow with NASA’s Hubble Space Telescope; the du Pont and Swope telescopes at Las Campanas, Chile, funded by the Carnegie Institution; the Subaru telescope on Mauna Kea, Hawaii, operated by the National Astronomical Observatory of Japan; and the Very Large Array, a stretch of 27 radio telescopes near Socorro, N.M., operated by the National Radio Astronomy Observatory.

The multi-wavelength observation of the July 9 burst, called GRB 050709, provided all the pieces of the puzzle to solve the short burst mystery.

“Powerful telescopes detected no supernova as the gamma-ray burst faded, arguing against the explosion of a massive star,” said Dr. George Ricker of MIT, HETE Principal Investigator and co-author of another Nature article. “The July 9 burst was like the dog that didn’t bark.”

Ricker added that the July 9 burst and probably the May 9 burst are located in the outskirts of their host galaxies, where old merging binaries are expected to be. Short gamma-ray bursts are not expected in young, star-forming galaxies. It takes billions of years for two massive stars, coupled in a binary system, to first evolve to the black hole or neutron star phase and then to merge. The transition of a star to a black hole or neutron star involves an explosion (supernova) that can kick the binary system far from its origin and out towards the edge of its host galaxy.

This July 9 burst and a later one on July 24 showed unique signals that point to not just any old merger but, more specifically, a black hole – neutron star merger. Scientists saw spikes of X-ray light after the initial gamma-ray burst. The quick gamma-ray portion is likely a signal of the black hole swallowing most of the neutron star. The X-ray signals, in the minutes to hours that followed, could be crumbs of neutron star material falling into the black hole, a bit like dessert.

And there’s more. Mergers create gravitational waves, ripples in spacetime predicted by Einstein but never detected directly. The July 9 burst was about two billion light years away. A big merger closer to the Earth could be detected by the National Science Foundation’s Laser Interferometer Gravitational-Wave Observatory (LIGO). If Swift detects a nearby short burst, LIGO scientists could go back and check the data with a precise time and location in mind.

“This is good news for LIGO,” said Dr. Albert Lazzarini, of LIGO Laboratory at Caltech. “The connection between short bursts and mergers firms up projected rates for LIGO, and they appear to be at the high end of previous estimates. Also, observations provide tantalizing hints of black hole – neutron star mergers, which have not been detected before. During LIGO’s upcoming yearlong observation we may detect gravitational waves from such an event.”

A black hole – neutron star merger would generate stronger gravitational waves than two merging neutron stars. The question now is how common and how close these mergers are. Swift, launched in November 2004, can provide that answer.

Original Source: NASA News Release

Mysterious dust cloud in various wavelengths. Image credit: CfA. Click to enlarge.
In an exercise that demonstrates the power of a multiwavelength investigation using diverse facilities, astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) have deciphered the true nature of a mysterious object hiding inside a dark cosmic cloud. They found that the cloud, once thought to be featureless, contains a baby star, or possibly a failed star known as a “brown dwarf,” that is still forming within its dusty cocoon.

Observations indicate that the mystery object has a mass about 25 times that of Jupiter, which would place it squarely in the realm of brown dwarfs. However, its mass may eventually grow large enough to qualify it as a small star. The object also is cool and faint, shining with less than 1/20 the sun’s luminosity.

“This object is the runt of the star formation family,” said CfA astronomer Tyler Bourke.

Establishing the true nature of the object required the unique capabilities of the Submillimeter Array (SMA) in Hawaii. “The SMA spotted what no single-dish telescope could see,” said Bourke.

Using the SMA, scientists detected a weak outflow of material predicted by star formation theories. That outflow – 10 times smaller in mass than any seen before – confirmed both the low-mass nature of the object and its association with the surrounding dark cloud. “The sensitivity and resolution of the Submillimeter Array with its multiple antennas were crucial in detecting the outflow,” said Bourke.

The puzzling object was discovered using a Smithsonian-developed infrared camera on board NASA’s Spitzer Space Telescope. Spitzer studied the dusty cosmic cloud named L1014 as part of the Cores to Disks Legacy program. A core is the densest region of a cloud, massive enough to make a star like the sun.

L1014, located about 600 light-years away in the constellation Cygnus the Swan, initially was classified as a “starless core” because it showed no evidence for star formation. Astronomers were surprised when Spitzer images revealed a faint infrared light source that appeared to be within the core.

Additional data were needed to confirm that the faint object was directly associated with the dark core, rather than being a chance superposition of a more distant, more mundane background object.

Near-infrared observations by the MMT Observatory in Arizona revealed a scattered light nebula surrounding the faint central object in L1014. “Light from the object is bouncing off surrounding dust and toward us,” said CfA astronomer Tracy Huard, who took the MMT images. “Reflection nebulosity like that is a fingerprint of an embedded object.”

The apparent size of the nebulosity indicated that the light source likely was located within L1014 and not in a more distant cloud. MMT data also gave investigators the orientation in space, or tilt, of the object within L1014. Astronomers then turned to the SMA for final confirmation.

“The Spitzer observations gave us hints to the nature of the object inside L1014. The MMT strengthened the association between the infrared source and the starless core. The Submillimeter Array clinched the case and revealed this object’s true identity,” said Bourke.

By studying faint, young objects like the one still forming within L1014, astronomers hope to learn more about the early stages of star formation.

“The most elusive part of star formation is the moment of birth,” said CfA astronomer Phil Myers. “In order to answer how it happens, you need examples of very young systems. This system is only about 10,000 to 100,000 years old – a baby as far as stars or brown dwarfs go.”

The combined capabilities of Spitzer, the SMA and the MMT were essential for finding and examining this object. Those facilities undoubtedly will prove useful in studying similar very dim, very young objects – objects so young that they are still growing. “They’re so young and faint that we can’t tell how much mass they will accumulate,” Myers added. “There’s no prenatal test for these objects. We’re not sure exactly what we’ll get in the end!”

A paper by Tyler L. Bourke et al. covering the SMA observations will be published in an upcoming issue of The Astrophysical Journal Letters and is available online at http://arxiv.org/abs/astro-ph/0509865.

A second paper by Tracy L. Huard et al. covering the MMT observations will be published in The Astrophysical Journal and is available online at http://arxiv.org/abs/astro-ph/0509302.

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: CfA News Release

Artist illustration of the 10th planet and its moon. Image credit: Caltech. Click to enlarge.
The newly discovered 10th planet, 2003 UB313, is looking more and more like one of the solar system’s major players. It has the heft of a real planet (latest estimates put it at about 20 percent larger than Pluto), a catchy code name (Xena, after the TV warrior princess), and a Guinness Book-ish record of its own (at about 97 astronomical units-or 9 billion miles from the sun-it is the solar system’s farthest detected object). And, astronomers from the California Institute of Technology and their colleagues have now discovered, it has a moon.

The moon, 100 times fainter than Xena and orbiting the planet once every couple of weeks, was spotted on September 10, 2005, with the 10-meter Keck II telescope at the W.M. Keck Observatory in Hawaii by Michael E. Brown, professor of planetary astronomy, and his colleagues at Caltech, the Keck Observatory, Yale University, and the Gemini Observatory in Hawaii. The research was partly funded by NASA. A paper about the discovery was submitted on October 3 to Astrophysical Journal Letters.

“Since the day we discovered Xena, the big question has been whether or not it has a moon,” says Brown. “Having a moon is just inherently cool-and it is something that most self-respecting planets have, so it is good to see that this one does too.”

Brown estimates that the moon, nicknamed “Gabrielle”-after the fictional Xena’s fictional sidekick-is at least one-tenth of the size of Xena, which is thought to be about 2700 km in diameter (Pluto is 2274 km), and may be around 250 km across.

To know Gabrielle’s size more precisely, the researchers need to know the moon’s composition, which has not yet been determined. Most objects in the Kuiper Belt, the massive swath of miniplanets that stretches from beyond Neptune out into the distant fringes of the solar system, are about half rock and half water ice. Since a half-rock, half-ice surface reflects a fairly predictable amount of sunlight, a general estimate of the size of an object with that composition can be made. Very icy objects, however, reflect a lot more light, and so will appear brighter-and thus bigger-than similarly sized rocky objects.

Further observations of the moon with NASA’s Hubble Space Telescope, planned for November and December, will allow Brown and his colleagues to pin down Gabrielle’s exact orbit around Xena. With that data, they will be able to calculate Xena’s mass, using a formula first devised some 300 years ago by Isaac Newton.

“A combination of the distance of the moon from the planet and the speed it goes around the planet tells you very precisely what the mass of the planet is,” explains Brown. “If the planet is very massive, the moon will go around very fast; if it is less massive, the moon will travel more slowly. It is the only way we could ever measure the mass of Xena-because it has a moon.”

The researchers discovered Gabrielle using Keck II’s recently commissioned Laser Guide Star Adaptive Optics system. Adaptive optics is a technique that removes the blurring of atmospheric turbulence, creating images as sharp as would be obtained from space-based telescopes. The new laser guide star system allows researchers to create an artificial “star” by bouncing a laser beam off a layer of the atmosphere about 75 miles above the ground. Bright stars located near the object of interest are used as the reference point for the adaptive optics corrections. Since no bright stars are naturally found near Xena, adaptive optics imaging would have been impossible without the laser system.

“With Laser Guide Star Adaptive Optics, observers not only get more resolution, but the light from distant objects is concentrated over a much smaller area of the sky, making faint detections possible,” says Marcos van Dam, adaptive optics scientist at the W.M. Keck Observatory, and second author on the new paper.

The new system also allowed Brown and his colleagues to observe a small moon in January around 2003 EL61, code-named “Santa,” another large new Kuiper Belt object. No moon was spotted around 2005 FY9-or “Easterbunny”-the third of the three big Kuiper Belt objects recently discovered by Brown and his colleagues using the 48-inch Samuel Oschin Telescope at Palomar Observatory. But the presence of moons around three of the Kuiper Belt’s four largest objects-Xena, Santa, and Pluto-challenges conventional ideas about how worlds in this region of the solar system acquire satellites.

Previously, researchers believed that Kuiper Belt objects obtained moons through a process called gravitational capture, in which two formerly separate objects moved too close to one another and become entrapped in each other’s gravitational embrace. This was thought to be true of the Kuiper Belt’s small denizens-but not, however, of Pluto. Pluto’s massive, closely orbiting moon, Charon, broke off the planet billions of years ago, after it was smashed by another Kuiper Belt object. Xena’s and Santa’s moons appear best explained by a similar origin.

“Pluto once seemed a unique oddball at the fringe of the solar system,” Brown says. “But we now see that Xena, Pluto, and the others are part of a diverse family of large objects with similar characteristics, histories, and even moons, which together will teach us much more about the solar system than any single oddball ever would.”

Original Source: Caltech News Release

Spiral Galaxy NGC 1350. Image credit: ESO. Click to enlarge.
Eighty-five million years ago on small planet Earth, dinosaurs ruled, ignorant of their soon-to-come demise in the great Jurassic extinction, while mammals were still small and shy creatures. The southern Andes of Bolivia, Chile, and Argentina were not yet formed and South America was still an island continent.

Eighty-five million years ago, our Sun and its solar system was 60,000 light years away from where it now stands [1].

Eighty-five million years ago, in another corner of the Universe, light left the beautiful spiral galaxy NGC 1350, for a journey across the universe. Part of this light was recorded at the beginning of the year 2000 AD by ESO’s Very Large Telescope, located on the 2,600m high Cerro Paranal in the Chilean Andes on planet Earth.

Astronomers classify NGC 1350 as an Sa(r) type galaxy, meaning it is a spiral with large central regions. In fact, NGC 1350 lies at the border between the broken-ring spiral type and a grand design spiral with two major outer arms. It is about 130,000 light-years across and, hence, is slightly larger than our Milky Way.

The rather faint and graceful outer arms originate at the inner main ring and can be traced for almost half a circle when they each meet the opposite arm, giving the impression of completing a second outer ring, the “eye”. The arms are given a blue tint as a result of the presence of very young and massive stars. The amount of dust, seen as small fragmented dust spirals in the central part of the galaxy and producing a fine tapestry that bear resemblance with blood vessels in the eye, is also a signature of the formation of stars.

The outer parts of the galaxy are so tenuous that many background galaxies can be seen shining through them, providing the observers with an awesome sense of depth. It is indeed quite remarkable to see that with a total exposure time of only 16 minutes, the VLT lets us admire such an incredible collection of island universes wandering about in the sky. ESO PR Photo 31b/05 is a mosaic of some of the most prominent galaxies found in the images. Some of these may reside as far as several billion light-years away, i.e. the light from these galaxies was emitted when the Sun and the Earth had not yet formed.

NGC 1350 is located in the rather inconspicuous southern Fornax (The Furnace) constellation [2]. Recessing from us at a speed of 1860 km/s [3], it is eighty-five million light-years away. It is thus most probably not a member of the Fornax cluster of galaxies, the most notable entity in the constellation, that lies about 65 million light-years away and contains the much more famous barred spiral NGC 1365. On the sky, NGC 1350 stands on the outskirts of the Fornax cluster as can be seen on this image taken with the 1m-Schmidt telescope at La Silla.

Original Source: ESO News Release

A distant supernova that exploded 41,000 years ago may have led to the extinction of the mammoth, according to research conducted by nuclear scientist Richard Firestone of the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab).

Firestone, who collaborated with Arizona geologist Allen West on this study, unveiled this theory Sept. 24 at the 2nd International Conference “The World of Elephants” in Hot Springs, SD. Their theory joins the list of possible culprits responsible for the demise of mammoths, which last roamed North America roughly 13,000 years ago. Scientists have long eyed climate change, disease, or intensive hunting by humans as likely suspects.

Now, a supernova may join the lineup. Firestone and West believe that debris from a supernova explosion coalesced into low-density, comet-like objects that wreaked havoc on the solar system long ago. One such comet may have hit North America 13,000 years ago, unleashing a cataclysmic event that killed off the vast majority of mammoths and many other large North American mammals. They found evidence of this impact layer at several archaeological sites throughout North America where Clovis hunting artifacts and human-butchered mammoths have been unearthed. It has long been established that human activity ceased at these sites about 13,000 years ago, which is roughly the same time that mammoths disappeared.

They also found evidence of the supernova explosion’s initial shockwave: 34,000-year-old mammoth tusks that are peppered with tiny impact craters apparently produced by iron-rich grains traveling at an estimated 10,000 kilometers per second. These grains may have been emitted from a supernova that exploded roughly 7,000 years earlier and about 250 light years from Earth.

“Our research indicates that a 10-kilometer-wide comet, which may have been composed from the remnants of a supernova explosion, could have hit North America 13,000 years ago,” says Firestone. “This event was preceded by an intense blast of iron-rich grains that impacted the planet roughly 34,000 years ago.”

In support of the comet impact, Firestone and West found magnetic metal spherules in the sediment of nine 13,000-year-old Clovis sites in Michigan, Canada, Arizona, New Mexico and the Carolinas. Low-density carbon spherules, charcoal, and excess radioactivity were also found at these sites.

“Armed with only a magnet and a Geiger counter, we found the magnetic particles in the well-dated Clovis layer all over North America where no one had looked before,” says Firestone.

Analysis of the magnetic particles by Prompt Gamma Activation Analysis at the Budapest Reactor and by Neutron Activation Analysis at Canada’s Becquerel Laboratories revealed that they are rich in titanium, iron, manganese, vanadium, rare earth elements, thorium, and uranium. This composition is very similar to lunar igneous rocks, called KREEP, which were discovered on the moon by the Apollo astronauts, and have also been found in lunar meteorites that fell to Earth in the Middle East an estimated 10,000 years ago.

“This suggests that the Earth, moon, and the entire solar system were bombarded by similar materials, which we believe were the remnants of the supernova explosion 41,000 years ago,” says Firestone.

In addition, Berkeley Lab’s Al Smith used the Lab’s Low-Background Counting Facility to detect the radioactive isotope potassium-40 in several Clovis arrowhead fragments. Researchers at Becquerel Laboratories also found that some Clovis layer sediment samples are significantly enriched with this isotope.

“The potassium-40 in the Clovis layer is much more abundant than potassium-40 in the solar system. This isotope is formed in considerable excess in an exploding supernova, and has mostly decayed since the Earth was formed,” says Firestone. “We therefore believe that whatever hit the Earth 13,000 years ago originated from a recently exploded supernova.”

Firestone and West also uncovered evidence of an even earlier event that blasted parts of the Earth with iron-rich grains. Three mammoth tusks found in Alaska and Siberia, which were carbon-dated to be about 34,000 years old, are pitted with slightly radioactive, iron-rich impact sites caused by high-velocity grains. Because tusks are composed of dentine, which is a very hard material, these craters aren’t easily formed. In fact, tests with shotgun pellets traveling 1,000 kilometers per hour produced no penetration in the tusks. Much higher energies are needed: x-ray analysis determined that the impact depths are consistent with grains traveling at speeds approaching 10,000 kilometers per second.

“This speed is the known rate of expansion of young supernova remnants,” says Firestone.

The supernova’s one-two punch to the Earth is further corroborated by radiocarbon measurements. The timeline of physical evidence discovered at Clovis sites and in the mammoth tusks mirrors radiocarbon peaks found in Icelandic marine sediment samples that are 41,000, 34,000, and 13,000 years old. Firestone contends that these peaks, which represent radiocarbon spikes that are 150 percent, 175 percent, and 40 percent above modern levels, respectively, can only be caused by a cosmic ray-producing event such as a supernova.

“The 150 percent increase of radiocarbon found in 41,000-year-old marine sediment is consistent with a supernova exploding 250 light years away, when compared to observations of a radiocarbon increase in tree rings from the time of the nearby historical supernova SN 1006,” says Firestone.

Firestone adds that it would take 7,000 years for the supernova’s iron-rich grains to travel 250 light years to the Earth, which corresponds to the time of the next marine sediment radiocarbon spike and the dating of the 34,000-year-old mammoth tusks. The most recent sediment spike corresponds with the end of the Clovis era and the comet-like bombardment.

“It’s surprising that it works out so well,” says Firestone.

Original Source: Berkeley Labs News Release

13 distant galaxies found in a sample of sky. Image credit: ESO. Click to enlarge.
It is one of the major goals of observational cosmology to trace the way galaxies formed and evolved and to compare it to predictions from theoretical models. It is therefore essential to know as precisely as possible how many galaxies were present in the Universe at different epochs.

This is easier to say than to do. Indeed, if counting galaxies from deep astronomical images is relatively straightforward, measuring their distance – hence, the epoch in the history of the universe where we see it [1] – is much more difficult. This requires taking a spectrum of the galaxy and measuring its redshift [2].

However, for the faintest galaxies – that are most likely the farthest and hence the oldest – this requires a lot of observing time on the largest of the telescopes. Until now, astronomers had thus to first carefully select the candidate high-redshift galaxies, in order to minimise the time spent on measuring the distance. But it seems that astronomers were too careful in doing so, and hence had a wrong picture of the population of galaxies.

It would be better to “simply” observe in a given patch of the sky all galaxies brighter than a given limit. But looking at one object at a time would make such a study impossible.

To take up the challenge, a team of French and Italian astronomers [3] used the largest possible telescope with a highly specialised, very sensitive instrument that is able to observe a very large number of (faint) objects in the remote universe simultaneously.

The astronomers made use of the VIsible Multi-Object Spectrograph (VIMOS) on Melipal, one of the 8.2-m telescopes of ESO’s Very Large Telescope Array. VIMOS can observe the spectra of about 1,000 galaxies in one exposure, from which redshifts, hence distances, can be measured. The possibility to observe two galaxies at once would be equivalent to using two VLT Unit Telescopes simultaneously. VIMOS thus effectively multiplies the efficiency of the VLT hundreds of times.

This makes it possible to complete in a few hours observations that would have taken months only a few years ago. With capabilities up to ten times more productive than competing instruments, VIMOS offers the possibility for the first time to conduct an unbiased census of the distant Universe.

Using the high efficiency of the VIMOS instrument, the team of astronomers embarked in the VIMOS VLT Deep Survey (VVDS) whose aim is to measure in some selected patch of the sky the redshift of all galaxies brighter than magnitude 24 in the red, that is, galaxies that are up to 16 million fainter than what the unaided eye can see.

In a total sample of about 8,000 galaxies selected only on the basis of their observed brightness in red light, almost 1,000 bright and vigorously star forming galaxies were discovered at an epoch 1,500 to 4,500 million years after the Big Bang (redshift between 1.4 and 5).

“To our surprise”, says Olivier Le F?vre, from the Laboratoire d’Astrophysique de Marseille (France) and co-leader of the VVDS project, “this is two to six times higher than had been found by previous works. These galaxies had been missed because previous surveys had selected objects in a much more restrictive manner than we did. And they did so to accommodate the much lower efficiency of the previous generation of instruments.”

While observations and models have consistently indicated that the Universe had not yet formed many stars in the first billion years of cosmic time, the discovery made by the scientists calls for a significant change in this picture.

Combining the spectra of all the galaxies in a given redshift range (i.e. belonging to the same epoch), the astronomers could estimate the amount of star formed in these galaxies. They find that the galaxies in the young Universe transform into stars between 10 and 100 times the mass of our Sun in a year.

“This discovery implies that galaxies formed many more stars early in the life of the Universe than had previously been thought”, explains Gianpaolo Vettolani, the other co-leader of the VVDS project, working at INAF-IRA in Bologna (Italy). “These observations will demand a profound reassessment of our theories of the formation and evolution of galaxies in a changing Universe.”

It now remains for astronomers to explain how one can create such a large population of galaxies, producing more stars than previously assumed, at a time when the Universe was about 10-20% of its current age.

Original Source: ESO News Release

Computer illustration of what the Universe’s first stars looked like. Image credit: CfA. Click to enlarge.
What did the very first stars look like? How did they live and die? Astronomers have ideas, but no proof. The first stars are so distant and formed so long ago that they are invisible to our best telescopes.

Until they explode. Hypernovas (more powerful cousins of supernovas) and their associated gamma-ray bursts offer astronomers the possibility of detecting light from the first generations of stars.

NASA’s Swift satellite already has seen a gamma-ray burst (GRB) with a redshift of 6.29, meaning that the progenitor star exploded about 13 billion years ago, when the universe was less than a billion years old. Theorists Volker Bromm (University of Texas at Austin) and Avi Loeb (Harvard-Smithsonian Center for Astrophysics) predict that one-tenth of the blasts Swift will spot during its operational lifetime will come from stars at a redshift of 5 or greater, that lived and died during the first billion years of the universe.

“Most of those GRBs will come from second generation or later stars,” said Loeb. “But if we get lucky, Swift may even detect a burst from one of the very first stars that formed — a star made of only hydrogen and helium.”

Calculations suggest that such stars, which are called Population III for historical reasons, would have been behemoths weighing 50-500 times as much as the Sun. A Population III star would have gulped its nuclear fuel faster than an SUV, dying quickly and explosively.

“Our best guess right now is that the recent GRB was not from a Pop III star. However, its redshift is high enough to make it very interesting,” said Bromm.

One key question examined by Bromm and Loeb is whether a Pop III star could have generated a GRB — a blast powerful enough to be seen from a distance of more than 13 billion light-years.

The answer they derived is a qualified yes. Pop III stars were massive enough to explode violently, leaving behind a black hole in most cases. However, a Pop III star likely would have to be part of a tight binary system to generate a GRB.

A close binary companion could strip the outer layers of a dying Pop III star, leaving less material to block the star’s explosive death throes. Jets of material generated from the newborn black hole therefore could punch their way out more easily, creating a burst of gamma-ray energy detectable across the universe.

About half of all nearby stars are members of binary or multiple star systems. The frequency of binaries, particularly close binaries, among Pop III stars remains unknown.

“Astronomers will address this question of the Pop III binary frequency using a dual approach, both observational and theoretical,” said Bromm. “By searching for high-redshift GRBs, we can constrain that number empirically. We also will try to improve simulations and make them detailed enough to model those details of star formation.”

If binary star systems are common among Pop III stars, then high-redshift GRBs could offer astronomers an ideal opportunity to study the first generation of stars.

“If Pop III binaries are common, Swift will be the first observatory to probe Population III star formation at high redshifts,” said Loeb.

This research has been submitted for publication to The Astrophysical Journal and is available online at http://arxiv.org/abs/astro-ph/0509303.

Original Source: CfA News Release

The centre of this infrared image shows the higher mass primary star (pink) and its lower mass companion. Image credit: CfA. Click to enlarge.
Newborn stars are difficult to photograph. They tend to hide in the nebulous stellar nurseries where they formed, enshrouded by thick layers of dust. Now, Smithsonian astronomer T.K. Sridharan (Harvard-Smithsonian Center for Astrophysics) and his colleagues have photographed a pair of stellar twins in infrared light, which penetrates the dust. And these babies are whoppers, weighing several times the mass of the Sun.

Moreover, Sridharan’s images reveal a circumstellar disk surrounding the more massive of the two stars. The presence of a disk suggests that massive, multiple-star systems form the same way as the Sun, by gradually accreting material from a gaseous disk.

“This system is the youngest massive binary ever to be directly imaged – only about 100,000 years old,” said Sridharan.

Sridharan and his colleagues studied an object known as IRAS 20126+4104, located more than 5,000 light-years away in the constellation Cygnus the Swan. IRAS 20126+4104 was suspected of harboring a binary star because outflows from the region wobbled back and forth like a spinning top. The wobble hinted at the gravitational tug of an unseen companion.

On several exceptionally clear and steady nights, the researchers were able to take highly detailed infrared images of this object using the UKIRT telescope on Mauna Kea, Hawaii. Those images revealed not one but two stars, as well as a dark dust lane where the inner parts of the disk, known from previous radio-wavelength observations, appeared nearly edge-on in silhouette.

“Many people have seen the iconic Hubble Space Telescope images of circumstellar disks around low-mass stars. This image is the equivalent for high-mass stars,” said Sridharan.

Between them the two stars weigh more than 10 times the mass of the Sun. Sridharan calculates that the surrounding disk contains at least one-tenth of a solar mass, which is enough material to make 100 Jupiter-sized worlds. The disk may be even more massive. It extends outward for at least 850 astronomical units, or 80 billion miles (more than 20 times the distance to Pluto). Interestingly, the smaller companion star currently is located at the same distance from the primary star, hinting that the companion’s gravity may play a role in limiting the outer reaches of the disk.

Sridharan said that the next step in studying this intriguing twin system is to get higher-resolution observations using adaptive optics or interferometry. Such data will yield a better estimate of the companion’s mass and a detailed profile of the disk.

“We are currently following several leads to investigate this star system, so stay tuned,” Sridharan added.

Sridharan’s co-authors are S.J. Williams and G.A. Fuller of UMIST (Manchester, UK). This research was published in the Sept. 20, 2005, issue of The Astrophysical Journal Letters and is available online at http://arxiv.org/abs/astro-ph/0508342.

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

Different concentrations of elements in a meteorite: magnesium is green, calcium is yellow, aluminium is white, iron is red and silicon is blue. Image credit: Open University. Click to enlarge.
Researchers trying to work out how the planets formed have uncovered a new clue by analysing meteorites that are older than the Earth.

The research shows that the process which depleted planets and meteorites of so-called volatile elements such as zinc, lead and sodium (in their gaseous form) must have been one of the first things to happen in our nebula. The implication is that ‘volatile depletion’ may be an inevitable part of planet formation – a feature not just of our Solar System, but of many other planetary systems too.

The researchers at Imperial College London, who are funded by the Particle Physics and Astronomy Research Council (PPARC), reached their conclusions after analysing the composition of primitive meteorites, stony objects that are older than the Earth and which have barely changed since the Solar System was made up of fine dust and gas.

Their analysis, published today in the Proceedings of the National Academy of Sciences, shows that all the components that make up these rocks are depleted of volatile elements. This means that volatile element depletion must have occurred before the earliest solids had formed.

All of the terrestrial planets in the Solar System as far out as Jupiter, including Earth, are depleted of volatile elements. Researchers have long known that this depletion must have been an early process, but it was unknown whether it occurred at the beginning of the formation of the Solar System, or a few million years later.

It might be that volatile depletion is necessary to make terrestrial planets as we know them -as without it our inner solar system would look more like the outer solar system with Mars and Earth looking more like Neptune and Uranus with much thicker atmospheres.

Dr Phil Bland, from Imperial’s Department of Earth Science and Engineering, who led the research, explains: “Studying meteorites helps us to understand the initial evolution of the early Solar System, its environment, and what the material between stars is made of. Our results answer one of a huge number of questions we have about the processes that converted a nebula of fine dust and gas into planets.”

Professor Monica Grady, a planetary scientist from the Open University and member of PPARC’s Science Committee adds, “This research shows how looking at the tiniest of fragments of material can help us answer one of the biggest questions asked: ‘How did the Solar System form?’. It is fascinating to see how processes that took place over 4.5 billion years ago can be traced in such detail in laboratories on Earth today.

For planetary scientists, the most valuable meteorites are those that are found immediately after falling to earth, and so are only minimally contaminated by the terrestrial environment. The researchers analysed around half of the approximately 45 primitive meteorite falls in existence around the world, including the Renazzo meteorite which was found in Italy in 1824.

Dr Phil Bland is a member of the Impacts and Astromaterials Research Centre (IARC), which combines planetary science researchers from Imperial College London and the Natural History Museum.

Original Source: PPARC News Release

Deep, wide field view of the Virgo Cluster showing a diffuse web of galaxies. Image credit: Chris Mihos et al. Click to enlarge.
Case Western Reserve University astronomers have captured the deepest wide-field image ever of the nearby Virgo cluster of galaxies, directly revealing for the first time a vast, complex web of “intracluster starlight” — nearly 1,000 times fainter than the dark night sky — filling the space between the galaxies within the cluster. The streamers, plumes and cocoons that make up this extremely faint starlight are made of stars ripped out of galaxies as they collide with one another inside the cluster, and act as a sort of “archaeological record” of the violent lives of cluster galaxies.

The Virgo image was captured through Case’s newly refurbished 24-inch Burrell Schmidt telescope, built in the 1930s and located at the Kitt Peak National Observatory in Arizona. Over the course of 14 dark moonless nights, the researchers took more than 70 images of the Virgo Cluster, then used advanced image processing techniques to combine the individual images into a single image capable of showing the faint intracluster light.

“When we saw all this very faint starlight in the image, my first reaction was WOW!,” project leader Chris Mihos said. “Then I began to worry about all the things we could have done wrong.” Many effects, such as stray light from nearby stars, from instruments in the observatory and even from the changing brightness of the night sky could all contaminate the image and lead to inaccurate results. “But as we corrected for each of these contaminants, not only did the faint starlight not disappear, it became even more apparent. That’s when we knew we had something big.”

The new image gives dramatic evidence of the violent life and death of cluster galaxies. Drawn together into giant clusters over the course of cosmic time by their mutual gravity, galaxies careen around in the cluster, smashing into other galaxies, being stripped apart by gravitational forces and even being cannibalized by the massive galaxies which sit at the cluster’s heart. The force of these encounters literally pulls many galaxies apart, leaving behind ghostly streams of stars adrift in the cluster, a faint tribute to the violence of cluster life.

“From computer simulations, we’ve long suspected this web of intracluster starlight should be there,” says Mihos, associate professor of astronomy at Case, “but it’s been extremely hard to map it out because it’s so faint.” Mihos and graduate students Craig Rudick (Case) and Cameron McBride (University of Pittsburgh, and former Case undergraduate) have developed computer simulations that track how clusters of galaxies evolve over time, to study exactly how this intracluster starlight is created.

“With the data from the telescope, we see how a cluster looks today,” Mihos explains. “But with computer simulations, we can watch how a cluster evolves over 10 billion years of time. By comparing the simulation to the real features we now see in Virgo, we can learn how the cluster formed and what happened to its many galaxies.” For example, the fact that the intracluster light in Virgo is so complex and irregular lends credence to the theory of “hierarchical assembly,” where clusters grow sporadically when groups of galaxies fall into the cluster, rather than through the smooth, slow addition of galaxies one by one.

To detect the faint intracluster light, upgrades were needed to Case’s Burrell Schmidt telescope, originally part of the original Warner and Swasey Observatory in Cleveland until its move to Kitt Peak in 1979. The improvements included the installation of a new camera system and upgrades to the telescope to make it more structurally stable and reduce unwanted scattered light.

“It’s like ‘The Little Engine that Could’,” says Case astronomer Paul Harding, who directed the refurbishment of the telescope. “It’s the smallest telescope on the mountain, but with these upgrades it’s capable of some pretty incredible science.” The telescope’s wide field of view — enough to fit three full moons across the image – proved crucial to the project, allowing the team to map out the intracluster light over a much larger part of the Virgo Cluster than would be possible using larger telescopes with their much smaller fields of view.
The Virgo Cluster of galaxies — so named because it appears in the constellation of Virgo — is the nearest galaxy cluster to the Earth, at a distance of approximately 50 million light years. The cluster contains more than 2,000 galaxies, the brightest of which can be seen with the aide of a small telescope.

The Case findings are reported in the paper “Diffuse Light in the Virgo Cluster” to be published in the September 20th issue of The Astrophysical Journal Letters. Along with Mihos team researchers included Case astronomers Heather Morrison and Paul Harding, and John Feldmeier, a National Science Foundation Fellow at the National Optical Astronomy Observatory in Tucson, Ariz. (and formerly of Case).

The wide-field image of the Virgo Cluster, along with movies of computer simulations of galaxies and galaxy clusters, can be found at http://astroweb.case.edu/hos/Virgo.

Original Source: Case Western University News Release