Category: Astronomy

Image credit: UCSC

A team of astronomers from the University of Cambridge have been researching a rare group of galaxies, known as dwarf spheroidal galaxies, which seem to have few stars but massive amounts of “dark matter”. The team analyzed one such galaxy and found that the stars in the outer edges were moving so quickly that the galaxy could only stay together if it had 100 times more dark matter than the mass of the stars alone. This research will help astronomers understand how galaxies are formed and how dark matter plays into their composition.

New research on dwarf spheroidal galaxies by a team of astronomers at the University of Cambridge promises a real astronomical first: detection, for the first time, of the true outer limits of a galaxy.

The team is presenting today (23 July 2003) at the 25th General Assembly of the International Astronomical Union (IAUXXV) in Sydney, Australia. The research could provide the key to understanding how larger galaxies were formed, including our own Milky Way galaxy.

The rare dwarf spheroidal galaxies display few stars but contain massive amounts of ‘dark matter’ or matter that does not emit radiation that can be observed by astronomers. The team studied these galaxies in detail using some of the largest optical telescopes on earth in order to probe their dark secrets. Dwarf spheroidal galaxies are widely believed to be the building blocks from which galaxies were formed.

By studying the motion of many stars the scientists have created a picture of how the mass of the galaxy is arranged. Surprisingly, when the Cambridge team looked at the stars at the edge of one such galaxy, Draco, they found that the outer stars were moving so quickly that the galaxy could only stay together if it contained 100 times more dark matter than the mass of the stars alone. Using detailed models of the motions of stars in a galaxy containing large quantities of dark matter, the group was able to demonstrate their observations could only be understood if the galaxy was surrounded by a large halo of dark matter.

Observations of the Ursa Minor dwarf spheroidal galaxy presented a new complication in the study. The team found an unexpected clump of slow-moving stars interpreted as the dead remains of one of the pure star systems, a globular cluster. The cluster should have been scattered across the galaxy, but it was still held together. The team realised this was only possible if the dark matter were arranged in a manner very differently from standard galaxies.

In May 2003, further research into Ursa Minor showed the stars in the very outermost parts are not moving quickly like the stars at the edge of Draco. Several theories are being investigated including dark matter from edge of Ursa Minor has been snatched away from the galaxy by its massive parent, the Milky Way, allowing some stars to wander gently away from their parent. Or they could be stars which wandered too close to other stars in the centre of the galaxy and were slung out to the edge of the galaxy as a result.

Whatever the explanation, the findings promise a real astronomical first: detection, for the first time, of the true outer limits of a galaxy.

Gerry Gilmore, Professor of Experimental Philosophy at the Institute of Astronomy at the University of Cambridge, said:

“This research, utilising some of the largest optical telescopes on earth, has provided us with insight to the makeup of these rare dwarf galaxies. This research helps astronomers better understand how galaxies were formed, and help take into account dark matter in all galaxies.”

Original Source: Cambridge University News Release

Image credit: SDSS

Since the discovery several years ago of a mysterious force, called dark energy, which seems to be accelerating the Universe, astronomers have been searching for additional evidence to either support or discount this theory. Astronomers from the Sloan Digital Sky Survey have found fluctuations in cosmic background radiation that match the repulsive influence of dark energy.

Scientists from the Sloan Digital Sky Survey announced the discovery of independent physical evidence for the existence of dark energy.

The researchers found an imprint of dark energy by correlating millions of galaxies in the Sloan Digital Sky Survey (SDSS) and cosmic microwave background temperature maps from NASA’s Wilkinson Microwave Anisotropy Probe (WMAP). The researchers found dark energy’s “shadow” on the ancient cosmic radiation, a relic of cooled radiation from the Big Bang.

With the combination of results from these two large sky surveys, this discovery provides physical evidence for the existence of dark energy; a result that complements earlier work on the acceleration of the universe as measured from distant supernovae. Observations from the Balloon Observations of Millimetric Extragalactic Radiation and Geophysics (BOOMERANG) of Cosmic Microwave Background (CMB) were also part of the earlier findings.

Dark energy, a major component of the universe and one of the greatest conundrums in science, is gravitationally repulsive rather than attractive. This causes the universe’s expansion to accelerate, in contrast to the attraction of ordinary (and dark) matter, which would make it decelerate.

“In a flat universe the effect we’re observing only occurs if you have a universe with dark energy,” explained lead researcher Dr. Ryan Scranton of the University of Pittsburgh’s Physics and Astronomy department. “If the universe was just composed of matter and still flat, this effect wouldn’t exist.”

“As photons from the cosmic microwave background (CMB) travel to us from 380,000 years after the Big Bang, they can experience a number of physical processes, including the Integrated Sachs-Wolfe effect. This effect is an imprint or shadow of dark energy on microwaves. The effect also measures the changes in temperature of cosmic microwave background due to the effects of gravity on the energy of photons”, added Scranton.

The discovery is “a physical detection of dark energy, and highly complementary to other detections of dark energy” added Dr. Bob Nichol, an SDSS collaborator and associate professor of physics at Carnegie Mellon University in Pittsburgh. Nichol likened the Integrated Sachs-Wolfe effect to looking at a person standing in front of a sunny window: “You just see their outline and can recognize them from just this information. Likewise the signal we see has the right outline (or shadow) that we’d expect for dark energy,” said Nichol.

“In particular the color of the signal is the same as the color of the cosmic microwave background, proving it is cosmological in origin and not some annoying contamination,” added Nichol.

“This work provides physical confirmation that one needs dark energy to simultaneously explain both the CMB and SDSS data, independent of the supernovae work. Such cross-checks are vital in science,” added Jim Gunn, Project Scientist of the SDSS and Professor of Astronomy at Princeton University.

Dr. Andrew Connolly of the University of Pittsburgh explained that photons streaming from the cosmic microwave background pass through many concentrations of galaxies and dark matter. As they fall into a gravitational well they gain energy (just like a ball rolling down a hill). As they come out they lose energy (again like a ball rolling up a hill). Photographic images of the microwaves become more blue (i.e. more energetic) as they fall in toward these supercluster concentrations and then become more red (i.e. less energetic) as they climb away from them.

“In a universe consisting mostly of normal matter one would expect that the net effect of the red and blue shifts would cancel. However in recent years we are finding that most of the stuff in our universe is abnormal in that it is gravitationally repulsive rather than gravitationally attractive,” explained Albert Stebbins, a scientist at the NASA/Fermilab Astrophysics Center Fermi National Accelerator Laboratory, an SDSS collaborating institution. “This abnormal stuff we call dark energy.”

SDSS collaborator Connolly said if the depth of the gravitational well decreases while the photon travels through it then the photon would exit with slightly more energy. “If this were true then we would expect to see that the cosmic microwave background temperature is slightly hotter in regions with more galaxies. This is exactly what we found.”

Stebbins added that the net energy change expected from a single concentration of mass is less than one part in a million and researchers had to look at a large number of galaxies before they could expect to see the effect. He said that the results confirm that dark energy exists in relatively small mass concentrations: only 100 million light years across where the previously observed effects dark energy were on a scale of 10 billion light years across. A unique aspect of the SDSS data is its ability to accurately measure the distances to all galaxies from photographic analysis of their photometric redshifts. “Therefore, we can watch the imprint of this effect on the CMB grow as a function of the age of the universe,” Connolly said. “Eventually we might be able to determine the nature of the dark energy from measurements like these, though that is a bit in the future.”

“To make the conclusion that dark energy exists we only have to assume that the universe is not curved. After the Wilkinson Microwave Anisotropy Probe results came in (in February, 2003), that’s a well-accepted assumption,” Scranton explained. “This is extremely exciting. We didn’t know if we could get a signal so we spent a lot of time testing the data against contamination from our galaxy or other sources. Having the results come out as strongly as they did was extremely satisfying.”

The discoveries were made in 3,400 square degrees of the sky surveyed by the SDSS.

“This combination of space-based microwave and ground-based optical data gave us this new window into the properties of dark energy,” said David Spergel, a Princeton University cosmologist and a member of the WMAP science team. “By combining WMAP and SDSS data, Scranton and his collaborators have shown that dark energy, whatever it is, is something that is not attracted by gravity even on the large scales probed by the Sloan Digital Sky Survey.

“This is an important hint for physicists trying to understand the mysterious dark energy,” Spergel added.

In addition to principal investigators Scranton, Connolly, Nichol and Stebbins, Istavan Szapudi of the University of Hawaii contributed to the research. Others involved in the analysis include Niayesh Afshordi of Princeton University, Max Tegmark of the University of Pennsylvania and Daniel Eisenstein of the University of Arizona.

ABOUT THE SLOAN DIGITAL SKY SURVEY (SDSS)
The Sloan Digital Sky Survey (sdss.org) will map in detail one-quarter of the entire sky, determining the positions and absolute brightness of 100 million celestial objects. It will also measure the distances to more than a million galaxies and quasars. The Astrophysical Research Consortium (ARC) operates Apache Point Observatory, site of the SDSS telescopes.

SDSS is a joint project of The University of Chicago, Fermilab, the Institute for Advanced Study, the Japan Participation Group, The Johns Hopkins University, the Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, University of Pittsburgh, Princeton University, the United States Naval Observatory, and the University of Washington.

Funding for the project has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Aeronautics and Space Administration, the National Science Foundation, the U.S. Department of Energy, the Japanese Monbukagakusho and the Max Planck Society.

The WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP) is a NASA mission built in partnership with Princeton University and the Goddard Space Flight Center to measure the temperature of the cosmic background radiation, the remnant heat from the Big Bang. The WMAP mission reveals conditions as they existed in the early universe by measuring the properties of the cosmic microwave background radiation over the full sky. (http://map.gsfc.nasa.gov)

Original Source: SDSS News Release

Image credit: ESO

Astronomers from the European Southern Observatory have found a whole new population of massive newborn stars inside a giant molecular cloud near the centre of the Milky Way. Inside the cloud are four massive stellar clusters with young stars as large as 120 times the mass of our Sun. This region, called W49, is one of the most energetic star forming regions of the Milky Way, and the recent observations help astronomers better understand how these regions form.

Peering into a giant molecular cloud in the Milky Way galaxy – known as W49 – astronomers from the European Southern Observatory (ESO) have discovered a whole new population of very massive newborn stars. This research is being presented today at the International Astronomical Union’s 25th General Assembly held in Sydney, Australia, by ESO-scientist Jo?o Alves.

With the help of infrared images obtained during a period of excellent observing conditions with the ESO 3.5-m New Technology Telescope (NTT) at the La Silla Observatory (Chile), the astronomers looked deep into this molecular cloud and discovered four massive stellar clusters, with hot and energetic stars as massive as 120 solar masses. The exceedingly strong radiation from the stars in the largest of these clusters is “powering” a 20 light-year diameter region of mostly ionized hydrogen gas (a “giant HII region”).

W49 is one of the most energetic regions of star formation in the Milky Way. With the present discovery, the true sources of the enormous energy have now been revealed for the first time, finally bringing to an end some decades of astronomical speculations and hypotheses.

Giant molecular clouds
Stars form predominantly inside Giant Molecular Clouds which populate our Galaxy, the Milky Way. One of the most prominent of these is W49, which has a mass of a million solar masses. It is located some 37,000 light-years away and is the most luminous star-forming region known in our home galaxy: its luminosity is several million times the luminosity of our Sun. A smaller region within this cloud is denoted W49A – this is one of the strongest radio-emitting areas known in the Galaxy.

Massive stars are excessive in all ways. Compared to their smaller and ligther brethren, they form at an Olympic speed and have a frantic and relatively short life. Formation sites of massive stars are quite rare and, accordingly, most are many thousands of light-years away. For that reason alone, it is in general much more difficult to observe details of massive-star formation.

Moreover, as massive stars are generally formed in the main plane of the Galaxy, in the disc where a lot of dust is present, the first stages of such stars are normally hidden behind very thick curtains. In the case of W49A, less than one millionth of the visible light emitted by a star in this region will find its way through the heavy intervening layers of galactic dust and reach the telescopes on Earth.

And finally, because massive stars just formed are still very deeply embedded in their natal clouds, they are anyway not detectable at optical wavelengths. Observations of this early phase of the lives of heavy stars must therefore be done at longer wavelengths (where the dust is more transparent), but even so, such natal dusty clouds still absorb a large proportion of the light emitted by the young stars.

Because of this observational obstacle, nobody had ever looked deep enough into the central most dense regions of the W49A molecular cloud – and nobody really knew what was in there. That is, until Jo?o Alves and his colleague, Nicole Homeier decided to obtain “deep” and penetrating observations of this mysterious area with the SofI near-infrared camera on the 3.5-m New Technology Telescope (NTT) at the ESO La Silla Observatory (Chile).

A series of infrared images was secured during a spell of good weather and very good atmospheric conditions (seeing about 0.5 arcsec). They clearly show the presence of a cluster of stars at the centre of a region of ionized hydrogen gas (an “HII-region”) measuring 20 light-years across. In addition, three other smaller clusters of stars were detected in the image.

Altogether, the ESO astronomers were able to identify more than one hundred heavy-weight stars inside W49A, with masses greater than 15 to 20 times the mass of our Sun. Among these, about thirty are located within the 20 light-year central region and about ten in each of the three other clusters.

The discovery of these hot and massive stars solves a long-standing problem concerning W49A: the exceptional brightness (in astronomical terminology: “luminosity”) of the entire region requires the energetic output from about one hundred massive stars, and nobody had ever seen them. But here they are on the deep and sharp SofI images!
Formation scenarios

The presence of such a large number of very massive stars spread over the entire region suggests that star formation in the various regions of W49A must have happened rather simultaneously from different seeds and not, as some theories propose, by a “domino-type” chain effect where stellar winds of fast particles and the emitted radiation of newly formed massive stars trigger another burst of star formation in the immediate neighbourhood.

The present research results also imply that star formation in W49A began earlier and extends over a larger area than previously thought.

Jo?o Alves is sure that this news will be received with interest by his colleagues: “W49A has long been known to radio astronomers as one of the most powerful star-forming region in the Galaxy with 30 or so massive baby-stars of the O-type, very deeply embedded in their parental cloud. What we have found is in fact quite amazing: this stellar maternity ward is much bigger than we first thought and it has not stopped forming stars yet. We now have evidence for no less than more than one hundred such stars in this region, way beyond the few dozen known until now”.

Nicole Homeier adds: “Above all, we uncovered four massive clusters in there, with stars as massive as 120 times the mass of our Sun – real ‘beasts’ that bombard their surroundings with incredibly intense stellar winds and strong ultraviolet light. This is not a nice place to live – and imagine, this is all inside our so-called ‘quiet Galaxy’!”

Original Source: ESO News Release

Image credit: CfA

Astronomers have found a distant galaxy with a core shaped like a warped pancake around its central supermassive black hole. The disk contains 400,000 times the mass of the Sun, and got its strange shape because the black hole is spewing material in two broad cones. This is different from most black holes, which channel the outflow into a thin, fast-moving jet.

While a person’s shape can be affected by pancakes, especially if you eat too many, you may not expect the same to be true on a cosmic scale. As it turns out, at least for the Circinus spiral galaxy, a pancake can shape an entire galactic nucleus. Astronomer Lincoln Greenhill (Harvard-Smithsonian Center for Astrophysics) and colleagues have found direct evidence for a “pancake” of gas and dust at the center of Circinus — a thin, warped disk surrounding the galaxy’s central, supermassive black hole.

That disk shapes the galaxy’s nucleus. It shadows different regions from the “glare” of the black hole, a glare created by the glow of accreting gas. And when some of this material is blown away from the black hole, as by radiation, the disk channels it, leaving shadowed regions in relative peace. This idea stands in contrast to the prevailing wisdom that shadows and outflows are caused by vast, thick “doughnuts” of dust and gas.

“We caught the Circinus galaxy and its black hole red-handed,” said Greenhill. “Most astronomers think that the center of an active galaxy has an outflow directed and channeled by a doughnut-shaped torus of dust and gas. Our detailed radio images show that the culprit is a warped disk. And if that’s true for the Circinus galaxy, then the same may be true for other active galaxies.”

Greenhill and his fellow astronomers identified the disk using the Australia Telescope Long Baseline Array, which is a network of radio telescopes 600 miles across. Only radio imaging can reveal directly such tiny structures inside galactic nuclei. The Circinus disk in particular is so deeply buried in a jumble of stars, gas, and dust that no optical telescope can detect it. They estimate the disk contains enough mass to form perhaps as many as 400,000 stars like our Sun, were it given a chance.

The Australian array picked up microwave signals from clouds rich in water vapor within both the warped edge-on disk and the outflow. The locations and velocities of the clouds provide strong evidence that the disk is channeling ejected material into two broad cones extending above and below the galactic plane.

“Water masers have been observed in broad, wide-angle outflows in star formation regions within our Galaxy, but this is the first time they have been observed associated with the nuclear region of an active galaxy,” said Simon Ellingsen (University of Tasmania), a co-author of the study. “These observations also are the first to show that this wide-angle outflow originates within about a third of a light-year from the galactic nucleus.”

A black hole is a massive object so compact and with such a powerful gravitational field that nothing can escape its pull once past the black hole’s event horizon. However, material can and does escape from regions near the black hole due to radiation pressure and inefficiencies of the accretion flow, among other things. The escaping material carries away angular momentum, allowing the remaining matter to fall into the black hole. The black hole in Circinus presents a stark contrast to other supermassive black holes whose outflows are channeled into long, narrow jets of material that blast out from the galactic nucleus.

“In the center of the Circinus galaxy, we see a black hole that spews out gas and dust in a broad spray like clouds of vapor from a steam locomotive. This presents us with a paradox. X-ray radiation from the nucleus of Circinus — radiation driven by the black hole — is as intense as for black holes in other active galaxies. In that way, the Circinus black hole appears to be typical. However, while other black holes drive narrow relativistic jets of plasma, the Circinus black hole drives a comparatively meek wind — one that can support the formation of delicate molecules and dust,” said Greenhill.

Greenhill and his colleagues plan to continue studying the nucleus of the Circinus galaxy to investigate the mechanism responsible for generating the outflow.

Original Source: CfA News Release

Image credit: NASA

A survey of stars in our neighbourhood has revealed those rich in metals, such as iron and titanium, are five times more likely to have planets orbiting them. The survey of 61 stars with planets and 693 stars without, revealed a distinct difference in the ‘metalicity’ of stars. Debra Fisher from the University of California, Berkley, says, “If you look at the metal-rich stars, 20 percent have planets. That’s stunning.” (contributed by Darren Osborne)

A comparison of 754 nearby stars like our sun – some with planets and some without – shows definitively that the more iron and other metals there are in a star, the greater the chance it has a companion planet.

“Astronomers have been saying that only 5 percent of stars have planets, but that’s not a very precise assessment,” said Debra Fischer, a research astronomer at the University of California, Berkeley. “We now know that stars which are abundant in heavy metals are five times more likely to harbor orbiting planets than are stars deficient in metals. If you look at the metal-rich stars, 20 percent have planets. That’s stunning.”

“The metals are the seeds from which planets form,” added colleague Jeff Valenti, an assistant astronomer at the Space Telescope Science Institute (STScI) in Baltimore, Md.

Fischer will present details of the analysis by her and Valenti at 1:30 p.m. Australian Eastern Standard Time (AEST) on Monday, July 21, at the International Astronomical Union meeting in Sydney, Australia.

Iron and other elements heavier than helium – what astronomers lump together as “metals” – are created by fusion reactions inside stars and sown into the interstellar medium by spectacular supernova explosions. Thus, while metals were extremely rare in the early history of the Milky Way galaxy, over time, each successive generation of stars became richer in these elements, increasing the chances of forming a planet.

“Stars forming today are much more likely to have planets than early generations of stars,” Valenti said. “It’s a planetary baby boom.”

As the number of extrasolar planets has grown – about 100 stars are now known to have planets – astronomers have noticed that stars rich in metals are more likely to harbor planets. A correlation between a star’s “metalicity” – a measure of iron abundance in a star’s outer layer that is indicative of the abundance of many other elements, from nickel to silicon – had been suggested previously by astronomers Guillermo Gonzalez and Nuno Santos based on surveys of a few dozen planet-bearing stars.

The new survey of metal abundances by Fischer and Valenti is the first to cover a statistically large sample of 61 stars with planets and 693 stars without planets. Their analysis provides the numbers that prove a correlation between metal abundance and planet formation.

“People have looked already in fair detail at most of the stars with known planets, but they have basically ignored the hundreds of stars that don’t seem to have planets. These under-appreciated stars provide the context for understanding why planets form,” said Valenti, who is an expert at determining the chemical composition of stars.

The data show that stars like the sun, whose metal content is considered typical of stars in our neighborhood, have a 5 to 10 percent chance of having planets. Stars with three times more metal than the sun have a 20 percent chance of harboring planets, while those with 1/3 the metal content of the sun have about a 3 percent chance of having planets. The 29 most metal-poor stars in the sample, all with less than 1/3 the sun’s metal abundance, had no planets.

“These data suggest that there is a threshold metalicity, and thus not all stars in our galaxy have the same chance of forming planetary systems,” Fischer said. “Whether a star has planetary companions or not is a condition of its birth. Those with a larger initial allotment of metals have an advantage over those without, a trend we’re now able to see clearly with this new data.”

The two astronomers determined metal composition by analyzing 1,600 spectra from more than 1,000 stars before narrowing the analysis to 754 stars that had been observed long enough to rule a gas giant planet in or out. Some of these stars have been observed for 15 years by Fischer, Geoffrey Marcy, professor of astronomy at UC Berkeley, and colleague Paul Butler, now at the Carnegie Institution of Washington, in their systematic search for extrasolar planets around nearby stars. All 754 stars were surveyed for more than two years, enough time to determine whether a close-in, Jupiter-size planet is present or not.

Though the surfaces of stars contain many metals, the astronomers focused on five – iron, nickel, titanium, silicon and sodium. After four years of analysis, the astronomers were able to group the stars by metal composition and determine the likelihood that stars of a certain composition have planets. With iron, for example, the stars were ranked relative to the iron content of the sun, which is 0.0032%.

“This is the most unbiased survey of its kind,” Fischer emphasized. “It is unique because all of the metal abundances were determined with the same technique and we analyzed all of the stars on our project with more than two years of data.”
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Fischer said the new data suggest why metal-rich stars are likely to develop planetary systems as they form. The data are consistent with the hypothesis that heavier elements stick together easier, allowing dust, rocks and eventually planetary cores to form around newly ignited stars. Since the young star and the surrounding disk of dust and gas would have the same composition, the metal composition observed from the star reflects the abundance of raw materials, including heavy metals, available in the disk to build planets. The data indicate a nearly linear relationship between amount of metals and the chance of harboring planets.

“These results tell us why some of the stars in our Milky Way galaxy have planets while others do not,” said Marcy. “The heavy metals must clump together to form rocks which themselves clump into the solid cores of planets.”

The research by Fischer and Valenti is supported by the National Aeronautics and Space Administration, the National Science Foundation, the Particle Physics and Astronomy Research Council (PPARC) in the United Kingdom, the Anglo-Australian Observatory, Sun Microsystems, the Keck Observatory and the University of California’s Lick Observatories.

Original Source: Berkeley News Release

Image credit: Hubble

Thousands of globular star clusters wander aimlessly between galaxies, in what was once thought to be ’empty space’. This is the finding of a joint US-UK project announced today at the International Astronomical Union General Assembly in Sydney. The group, lead by Dr. Michael West of the University of Hawaii, believes these clusters were ‘torn’ away from their parent galaxies and now drift as orphans. (contributed by Darren Osborne)

US and UK astronomers have discovered a population of previously unknown star clusters in what was thought to be the empty space between galaxies. The research is being presented today at the International Astronomical Union?s 25th General Assembly being held in Sydney, Australia, by Dr. Michael West of the University of Hawaii.

Most galaxies are surrounded by tens, hundreds or even thousands of ancient star clusters, which swarm around them like bees around a hive. Our own Milky Way galaxy has about 150 of these ?globular clusters?, as they are called. Globular clusters are systems of up to a million stars compacted together by gravity into dense sphere-shaped groupings. Studies of globular clusters have provided many important insights over the years into the formation of their parent galaxies.

The discovery of this new type of star cluster was made using images obtained last year with the Hubble Space Telescope and the giant 10-meter Keck Telescope on Mauna Kea, Hawaii. ?We found a large number of ?orphaned? globular clusters,? said Dr West. ?These clusters are no longer held within the gravitational grip of galaxies, and seem to be wandering freely through intergalactic space like cosmic vagabonds.?

Although the lonely existence of such star clusters had been predicted for half a century, it is only now that astronomers have finally been able to confirm their existence. Dr West?s team published preliminary findings about its discovery in April this year, and is today presenting new results at the International Astronomical Union?s 25th General Assembly, being held in Sydney, Australia.

?The new data from the Hubble Space Telescope and Keck Telescope confirm our discovery, and are providing new insights to the origin of these objects,? said Dr West.

According to West, these globular star clusters probably once resided in galaxies just like most of the normal globular clusters that we see in nearby galaxies today. However, the pull of gravity from a passing galaxy can rip stars and star clusters loose — in some cases entire galaxies can be damaged or destroyed by violent collisions or by the collective gravitational pull from their galactic neighbors.

It is thought that the partial or complete destruction of their parent galaxies spilled the globular star clusters into intergalactic space.

Finding these globular clusters hasn?t been easy. With only one exception, all of the intergalactic globular clusters the teams have detected are so far away (millions of light-years) that they just look like tiny points of light in a vast sea of blackness.

?Because they’re so far away these objects are very faint, almost a billion times fainter than the unaided human eye can see,? said Dr West. ?Detecting such faint objects pushes the limits of even what the Hubble Space Telescope can do.?

?By studying these intergalactic vagabonds in greater detail we hope to learn more about the numbers and types of galaxies that may have been destroyed so far during the life of the universe,? said Dr West. ?Some of these star clusters might also eventually be ?adopted? by other galaxies if they stray close enough to be captured by their gravity.?

The researchers are currently analyzing new Hubble Space Telescope images they recently obtained, and are planning to obtain more at the end of this year.

Original Source: University of Hawaii News Release

If you’re interested in science and discovery in general, I’d like to suggest two weekly, hour-long radio shows that you should tune into – through the Internet.

• Quirks and Quarks – Every Canadian reader will know exactly what I’m talking about. This is a weekly radio show on the Canadian Broadcasting Channel hosted by Bob McDonald. They have archives available online going back almost 10 years.
• NPR Science Friday – Every Friday, NPR’s Talk of the Nation is taken over by Ira Flatow to discuss the latest happening in science. It’s a great show.

Both are well worth your time. Check them out.

Fraser Cain
Publisher
Universe Today

Image credit: Hubble

A new article published in the journal Nature helps settle a long-time mystery about some of the earliest solid particles in the Universe. By measuring supernova remnant Cassiopeia A with the very precise SCUBA telescope, astronomers were able to detect enormous quantities of cosmic dust below -257 degrees Celsius. Hot dust had been found in the past, but the colder dust was mostly invisible – until now. It appears that supernovae are extremely efficient at producing the dust that later forms planets, rocks, and people.

We have just discovered that some supernovae have bad habits – they belch out huge quantities of smoke, known as cosmic dust. This solves a long-standing mystery over the origin of cosmic dust and suggests that supernovae, which are exploding stars, were responsible for producing the first ever solid particles in the Universe.

The Prime Suspects
Supernovae are the violent explosions of stars occurring at the end of their lives. They occur around every 50 years or so in our Galaxy and there are two main types – Type Ia and II. Type II are the explosions of very massive stars with mass greater than 8 times the mass of the Sun (Msun). These stars are ‘live fast – die young’ using up their hydrogen and helium fuel in only a few million years, thousands of times faster than the Sun burns it’s fuel. When the fuel supply is exhausted the star must burn heavier and heavier elements until, finally, when it can do no more to keep itself alive the inner parts of the star collapse to form a neutron star or Black Hole, and the outer parts are flung off in the cataclysm we call a supernova. The enormous explosion sweeps up the surrounding gas into a shell which shines at X-ray, optical and radio wavelengths, and sends shock waves through the galaxy. Supernovae release more energy in a single instant than the Sun will produce in its whole life-time. If the nearest massive star, Betelgeuse in the constellation Orion, were to go supernova it would (for a short time) be brighter than the full moon.

The Cosmic Smoke-Screen
Interstellar dust consists of tiny particles of solid material floating around in the space between the stars – with sizes typically that of cigarette smoke. It is not the same as the dust we clean up in our houses, and in fact the Earth is a giant lump of cosmic dust! It is responsible for blocking about half of all the light emitted from stars and galaxies and profoundly affects our view of the Universe. This ‘dusty’ cloud has a silver lining though, as the astronomers can `see’ the dust radiating the stolen starlight using special cameras designed to work at longer wavelengths, in the Infra-Red (IR: 10 – 100 microns) and Submillimeter (sub-mm: 0.3 – 1mm) part of the electromagnetic spectrum. One such camera is called SCUBA and it is located on the James Clerk Maxwell Telescope in Hawaii. SCUBA is a UK-built instrument which detects light-waves at sub-mm wavelengths and is able to see dust right out to where the furthest stars and galaxies are found.

Dusty Beginnings
Recent observations with SCUBA have shown that a huge amount of dust exists in galaxies and quasars when the Universe was only 1/10th of its present age, long before the Earth and solar system had formed. The presence of all this dust in the distant Universe has a great impact on what astronomers are able to see with their giant optical telescopes, as it limits the amount of starlight which can escape from a distant galaxy and be seen on Earth.

That there were so many solid particles in Universe at such an early time was a great surprise to astronomers as they had believed that dust was mainly formed in cool winds from red giant stars near the end of their lives. Since it takes a long time for star to reach this stage in its evolution (the Sun will take around 9 billion years) there has simply not been enough time for so much dust to have been made in this way.

‘Dust has been swept under the cosmic carpet – for years astronomers have treated it as a nuisance because of the way it hides the light from the stars. But then we found that there is dust right at the edge of the Universe, in the earliest stars and galaxies, and we realised that we were ignorant of even its basic origin’ explained Dr Dunne.

Supernovae also make large amounts of heavy elements, such as carbon and oxygen, and throw them out into interstellar space. These are the elements which make up our bodies and, since they are also the elements which make up dust grains, supernovae have long been a prime suspect in the mystery of the origin of cosmic dust. As it takes only a few million years for the most massive stars to reach the end of lives and explode as supernovae, they could make dust quickly enough to explain what is seen in the early Universe. However, until this team’s work, only tiny amounts of dust had ever been found in supernovae – leaving astronomers with a smoking gun but no ‘smoke’

Haley Morgan, a PhD student at Cardiff said ‘If supernovae were efficient dust ‘factories’ they would each be producing more than the mass of the Sun in dust.’

‘As massive stars evolve to become supernovae in the blink of an eye by astronomical standards, they could easily explain why the early Universe appears so dusty.’ added Dr Rob Ivison of the Royal Observatory Edinburgh.

Supernova Sleuths
The team from Cardiff and Edinburgh used SCUBA to look for the emission from dust in the remains of a recent supernova. Cassiopeia A is the remnant of a supernova which happened around 320 years ago. It is located in the constellation Cassiopeia, 11,000 light years from Earth and is about 10 light years across. Cas A is the brightest radio source in the sky so it is well studied at many wavelengths from the optical to X-rays. The images below show Cas A in the X-rays, optical, infra-red and radio. The X-rays follow the really hot gas (10 million degrees Kelvin), and the other wavelengths trace material at: 10 thousand degrees (optical), hot dust at 100 K (IR) and high energy electrons (radio).

Although astronomers had been searching for dust in supernova remnants for decades, they had used instruments which could only detect dust that was quite warm, such as that in the ISO infra-red image above. SCUBA has the advantage here because it is able to see dust which is very cold and this is because it works at longer sub-mm wavelengths.

‘In the same way that you can only see an iron poker glowing when it’s been in a fire, you can only see dust with infra-red cameras when it is warmer than about 25 Kelvin, but SCUBA can see it when it’s colder too’ explained Dr Steve Eales, Reader in Astrophysics at Cardiff University.

Cold Hard Evidence
SCUBA found a large amount of dust in the Cas A remnant, 1-4 times more than the mass of the Sun ! This is over 1,000 times more than had been seen before. This means that Cas A was very efficient at creating dust from the elements available. The temperature of the dust is very low, only 18 Kelvin (-257 degrees Celsius), and this is the reason that it had never been seen before. Below are the two sub-mm images of Cas A at 850 and 450 microns taken with SCUBA. You can see that the left image looks a little like the radio one above, and this is because the high energy electrons which make the radio image also emit some of their energy at slightly shorter wavelengths – contaminating the sub mm emission at 850microns. The middle image is at 450 microns where the contamination is much lower, and so most of this emission is from cold dust. If we remove the contamination we get a different picture (right). All the dust is seen in the bottom half of the remnant and the two sub-mm images now look much more similar!
850 microns without radio contamination

‘The puzzle is how the dust can remain so cold when we know that there is gas at over a million degrees present from the X-ray radiation it gives off.’ commented Prof. Mike Edmunds, head of the School of Physics & Astronomy in Cardiff.

The dust also has different properties to the ‘everyday’ kind of dust in the Milky Way and other galaxies – it is better at ‘shining’ in the sub-mm, maybe because it is still very young and relatively pristine. If all supernovae were this efficient at making dust they would be the biggest dust ‘factories’ in the Galaxy. Smoking supernovae provide a solution to the mystery of the huge amounts of dust seen in the early Universe.

‘These observations give us a tantalising glimpse of how the first solid particles in the Universe were created’ said Haley Morgan.

Original Source: Cardiff University News Release

Image credit: ESO

Astronomers from the European Southern Observatory have found a very rare “Einstein ring” gravitational lens, where the light from a distant quasar is warped and magnified by the gravity of a closer galaxy. The two objects are so closely aligned that the image of the quasar forms a ring around the galaxy from our vantage point here on Earth. With careful measurements, the team was able to determine that the quasar is 6.3 billion light-years away, and the galaxy is only 3.5 billion light-years away, making it the closest gravitational lens ever discovered.

Using the ESO 3.6-m telescope at La Silla (Chile), an international team of astronomers [1] has discovered a complex cosmic mirage in the southern constellation Crater (The Cup). This “gravitational lens” system consists of (at least) four images of the same quasar as well as a ring-shaped image of the galaxy in which the quasar resides – known as an “Einstein ring”. The more nearby lensing galaxy that causes this intriguing optical illusion is also well visible.

The team obtained spectra of these objects with the new EMMI camera mounted on the ESO 3.5-m New Technology Telescope (NTT), also at the La Silla observatory. They find that the lensed quasar [2] is located at a distance of 6,300 million light-years (its “redshift” is z = 0.66 [3]) while the lensing elliptical galaxy is rougly halfway between the quasar and us, at a distance of 3,500 million light-years (z = 0.3).

The system has been designated RXS J1131-1231 – it is the closest gravitationally lensed quasar discovered so far.

Cosmic mirages
The physical principle behind a “gravitational lens” (also known as a “cosmic mirage”) has been known since 1916 as a consequence of Albert Einstein’s Theory of General Relativity. The gravitational field of a massive object curves the local geometry of the Universe, so light rays passing close to the object are bent (like a “straight line” on the surface of the Earth is necessarily curved because of the curvature of the Earth’s surface).

This effect was first observed by astronomers in 1919 during a total solar eclipse. Accurate positional measurements of stars seen in the dark sky near the eclipsed Sun indicated an apparent displacement in the direction opposite to the Sun, about as much as predicted by Einstein’s theory. The effect is due to the gravitational attraction of the stellar photons when they pass near the Sun on their way to us. This was a direct confirmation of an entirely new phenomenon and it represented a milestone in physics.

In the 1930’s, astronomer Fritz Zwicky (1898 – 1974), of Swiss nationality and working at the Mount Wilson Observatory in California, realised that the same effect may also happen far out in space where galaxies and large galaxy clusters may be sufficiently compact and massive to bend the light from even more distant objects. However, it was only five decades later, in 1979, that his ideas were observationally confirmed when the first example of a cosmic mirage was discovered (as two images of the same distant quasar).

Cosmic mirages are generally seen as multiple images of a single quasar [2], lensed by a galaxy located between the quasar and us. The number and the shape of the images of the quasar depends on the relative positions of the quasar, the lensing galaxy and us. Moreover, if the alignment were perfect, we would also see a ring-shaped image around the lensing object. Such “Einstein rings” are very rare, though, and have only been observed in a very few cases.

Another particular interest of the gravitational lensing effect is that it may not only result in double or multiple images of the same object, but also that the brightness of these images increase significantly, just as it happens with an ordinary optical lens. Distant galaxies and galaxy clusters may thereby act as “natural telescopes” which allow us to observe more distant objects that would otherwise have been too faint to be detected with currently available astronomical telescopes.

Image sharpening techniques resolve the cosmic mirage better
A new gravitational lens, designated RXS J1131-1231, was serendipitously discovered in May 2002 by Dominique Sluse, then a PhD student at ESO in Chile, while inspecting quasar images taken with the ESO 3.6-m telescope at the La Silla Observatory. The discovery of this system profited from the good observational conditions prevailing at the time of the observations. From a simple visual inspection of these images, Sluse provisionally concluded that the system had four star-like (the lensed quasar images) and one diffuse (the lensing galaxy) component.

Because of the very small separation between the components, of the order of one arcsecond or less, and the unavoidable “blurring” effect caused by turbulence in the terrestrial atmosphere (“seeing”), the astronomers used sophisticated image-sharpening software to produce higher-resolution images on which precise brightness and positional measurements could then be performed (see also ESO PR 09/97). This so-called “deconvolution” technique makes it possible to visualize this complex system much better and, in particular, to confirm and render more conspicuous the associated Einstein ring, cf. PR Photo 20a/03.

Identification of the source and of the lens
The team of astronomers [1] then used the ESO 3.5-m New Technology Telescope (NTT) at La Silla to obtain spectra of the individual image components of this lensing system. This is imperative because, like human fingerprints, the spectra allow unambiguous identification of the observed objects.

Nevertheless, this is not an easy task because the different images of the cosmic mirage are located very close to each other in the sky and the best possible conditions are needed to obtain clean and well separated spectra. However, the excellent optical quality of the NTT combined with reasonably good seeing conditions (about 0.7 arcsecond) enabled the astronomers to detect the “spectral fingerprints” of both the source and the object acting as a lens, cf. ESO PR Photo 20b/03.

The evaluation of the spectra showed that the background source is a quasar with a redshift of z = 0.66 [3], corresponding to a distance of about 6,300 million light-years. The light from this quasar is lensed by a massive elliptical galaxy with a redshift z=0.3, i.e. at a distance of 3,500 million light-years or about halfway between the quasar and us. It is the nearest gravitationally lensed quasar known to date.

Because of the specific geometry of the lens and the position of the lensing galaxy, it is possible to show that the light from the extended galaxy in which the quasar is located should also be lensed and become visible as a ring-shaped image. That this is indeed the case is demonstrated by PR Photo 20a/03 which clearly shows the presence of such an “Einstein ring”, surrounding the image of the more nearby lensing galaxy.

Micro lensing within macro lensing ?
The particular configuration of the individual lensed images observed in this system has enabled the astronomers to produce a detailed model of the system. From this, they can then make predictions about the relative brightness of the various lensed images.

Somewhat unexpectedly, they found that the predicted brightnesses of the three brightest star-like images of the quasar are not in agreement with the observed ones – one of them turns out to be one magnitude (that is, a factor of 2.5) brighter than expected. This prediction does not call into question General Relativity but suggests that another effect is at work in this system.

The hypothesis advanced by the team is that one of the images is subject to “microlensing”. This effect is of the same nature as the cosmic mirage – multiple amplified images of the object are formed – but in this case, additional light-ray deflection is caused by a single star (or several stars) within the lensing galaxy. The result is that there are additional (unresolved) images of the quasar within one of the macro-lensed images.

The outcome is an “over-amplification” of this particular image. Whether this is really so will soon be tested by means of new observations of this gravitational lens system with the ESO Very Large Telescope (VLT) at Paranal (Chile) and also with the Very Large Array (VLA) radio observatory in New Mexico (USA).

Outlook
Until now, 62 multiple-imaged quasars have been discovered, in most cases showing 2 or 4 images of the same quasar. The presence of elongated images of the quasar and, in particular, of ring-like images is often observed at radio wavelengths. However, this remains a rare phenomenon in the optical domain – only four such systems have been imaged by optical/infrared telecopes until now.

The complex and comparatively bright system RXS J1131-1231 now discovered is a unique astrophysical laboratory. Its rare characteristics (e.g., brightness, presence of a ring-shaped image, small redshift, X-ray and radio emission, visible lens, …) will now enable the astronomers to study the properties of the lensing galaxy, including its stellar content, structure and mass distribution in great detail, and to probe the source morphology. These studies will use new observations which are currently being obtained with the VLT at Paranal, with the VLA radio interferometer in New Mexico and with the Hubble Space Telescope.
More information

The research described in this press release is presented in a Letter to the Editor, soon to appear in the European professional journal Astronomy & Astrophysics (“A quadruply imaged quasar with an optical Einstein ring candidate : 1RXS J113155.4-123155”, by Dominique Sluse et al.).

More information on gravitational lensing and on this research group can also be found at the URL : http://www.astro.ulg.ac.be/GRech/AEOS/.

Notes
[1]: The team consists of Dominique Sluse, Damien Hutsem?kers, and Thodori Nakos (ESO and Institut d’Astrophysique et de G?ophysique de l’Universit? de Li?ge – IAGL), Jean-Fran?ois Claeskens, Fr?d?ric Courbin, Christophe Jean, and Jean Surdej (IAGL), Malvina Billeres (ESO), and Sergiy Khmil (Astronomical Observatory of Shevchentko University).

[2]: Quasars are particularly active galaxies, the centres of which emit prodigious amounts of energy and energetic particles. It is believed that they harbour a massive black hole at their centre and that the energy is produced when surrounding matter falls into this black hole. This type of object was first discovered in 1963 by the Dutch-American astronomer Maarten Schmidt at the Palomar Observatory (California, USA) and the name refers to their “star-like” appearance on the images obtained at that time.

[3]: In astronomy, the “redshift” denotes the fraction by which the lines in the spectrum of an object are shifted towards longer wavelengths. Since the redshift of a cosmological object increases with distance, the observed redshift of a remote galaxy also provides an estimate of its distance.

Original Source: ESO News Release

Image credit: ANU

An Australian astronomer has discovered 20 galaxies that contain mostly gas, rather than stars – revising the definition of “galaxy”. These galaxies are giant discs of gas, tens of thousands of light-years across, and contain the mass of billions of sun, but for some reason their hydrogen hasn’t coalesced into stars like regular galaxies. The discovery of these gas galaxies will help astronomers better understand what it takes for a galaxy to form.

Any dictionary will tell you that a galaxy is a vast collection of stars, floating deep in space. But this definition may need revision following new research by an ANU graduate student who has discovered galaxies that consist mostly of gas, rather than stars.

In research to be presented to the General Assembly of the International Astronomical Union in Sydney today, Brad Warren will reveal his discovery of twenty gassy galaxies, which have very few stars.

?When you look for gas [in these galaxies] the signal just booms in,? Mr Warren said. ?But when you look for stars, all you see is a barely recognisable smudge.?

The galaxies are vast discs of hydrogen, tens of thousands of light years across, weighing more than a billion suns, with a tiny number of barely visible stars in their centre.

For an unknown reason, they have not transformed their rich source of hydrogen gas into masses of stars like their brilliant, twinkling counterparts.

?Hydrogen is the most common element in the Universe and it forms the building blocks for stars,? Mr Warren said.

?Most galaxies, like our own Milky Way, have transformed most of their gas into stars but the galaxies we have discovered have held back and we are not sure why.

?Discovering this missing link will give us important insights into how, when and why galaxies, such as our own, formed.?

Although the existence of gassy galaxies has been documented in the past, it is the first time they have been discovered with such prominent discrepancies between the amount of hydrogen gas and stars.

?This research throws up a further challenge in the ongoing quest to discover the secrets of the Universe,? Mr Warren said.

Mr Warren, from the Research School of Astronomy and Astrophysics, collaborated with fellow ANU researcher, Dr Helmut Jerjen, and Dr Baerbel Koribalski, from CSIRO?s Australia Telescope National facility.

The team used three of Australia?s most powerful telescopes for their research – the Parkes Radio Telescope; the Australia Telescope Compact Array near Narrabri and the University?s 2.3 metre telescope at Siding Spring Observatory, Coonabarabran.

Original Source: ANU News Release