Category: Astronomy

Image credit: Hubble

New research from the Hubble Space Telescope indicates that the majority of large dying Wolf-Rayat stars have a smaller companion star orbiting nearby. This discovery will help astronomers understand how these unique stars evolve in the Universe, and could provide new a new method to estimate their size. Wolf-Rayat stars start out at least 20 times the mass of the Sun, last only a few million years, and then explode as supernovae. It’s now believed that these stars and their companions transfer mass as they orbit one another.

The majority of massive and brilliant but dying “Wolf-Rayet” stars have company – a smaller companion star orbiting nearby, according to new observations using the Hubble Space Telescope. The result will help astronomers understand how the biggest stars in the Universe evolve. It may also resolve the mystery of impossibly massive stars, and calls into question a certain kind of distance estimate that uses the apparent brightness of starlight.

Wolf-Rayet (WR) stars begin life as cosmic titans, with at least 20 times the mass of the Sun. They live fast and die hard, exploding as supernova and blasting vast amounts of heavy elements into space for use in later generations of stars and planets. “I tell people I study the stars that made a lot of the carbon in their bodies and the gold in their jewelry,” says Dr. Debra Wallace of NASA’s Goddard Space Flight Center, Greenbelt, Md. “Understanding how Wolf-Rayet stars evolve is a critical link in the chain of events that ultimately led to life.” Wallace is lead author of papers on this research to be published in the Astronomical Journal and the Astrophysical Journal.

By the time these stars are near the end of their brief lifetimes, during the “Wolf-Rayet” phase, they are fusing heavy elements in their cores in a frantic bid to prevent collapsing under their own immense mass. This generates intense heat and radiation that drives fierce, 2.2 million to 5.4 million mile-per-hour (3.6 million to 9 million km/hr) stellar winds characteristic of WR stars (Image 1). These winds blow off the outer layers of WR stars, greatly reducing their mass and compressing nearby interstellar clouds, triggering their gravitational collapse and igniting a new generation of stars.

Because cosmic distances are so great, what appears as a single star even when viewed through large telescopes (Image 2) may in fact be two or more stars orbiting each other (Images 3 and 4). In the new research, Wallace and her team used the superior resolving power of the Planetary Camera in the Wide-Field Planetary Camera 2 instrument on board Hubble to identify new potential companion stars for 23 of 61 WR stars in our galaxy. Although the apparent companion stars need to be confirmed with a light-analysis technique called spectroscopy, the team was conservative in declaring nearby stars companions.

“The portion of Wolf-Rayet stars having visually identified companion stars zoomed from 15 percent before Hubble to 59 percent with our observations, which included a quarter of the known WR stars in our galaxy,” said Wallace. “I wouldn’t be surprised if future observations reveal companions around an even greater percentage of them.”

The presence of a companion star should significantly influence how these stars evolve, according to the team. One of many possible influences is mass transfer. If the stars come close together at some point in their orbits, their gravitational interaction could cause one to transfer gas to the other, significantly altering their masses over time. Since more massive stars use up their fuel much faster than less massive stars, such a mass transfer could significantly change their lifetimes. Other influences include altering orbits, rotation rates, or mass-loss rates through the pull of their gravity, and the impact of stellar winds. “Astronomers assumed Wolf-Rayet stars were single when trying to calculate how they evolve, but we are finding most have company,” said Wallace. “It’s like thinking married life will be the same as life as a bachelor. A companion star has got to change the life of these stars somehow.”

Since what is seen as one star may in fact be two or even more, stupendous mass estimates of more than a hundred times that of the Sun for certain stars may have to be revised downward. “This actually helps clear up an apparent mystery, because astronomers believe there is a limit to how big a star can be,” said Wallace. “The more massive a star, the faster it consumes its fuel and the brighter it shines. Above about 100 solar masses, a star should essentially blow itself apart through its intense radiation.”

The result also makes a common technique for estimating distances to these stars more uncertain. To get a distance estimate to a star, one gets the spectral type of the star, an analysis of the star’s light that reveals its unique characteristics, like a fingerprint. For a given spectral type, one knows the star’s average absolute luminosity (how bright it would be if it were a certain distance – 32.6 light-years – away). By measuring its apparent luminosity (how bright it appears to be at its actual, but unknown, distance), one can then use the relationship between its apparent and absolute luminosity to determine the actual distance. If there are really two (or more) stars there that you don’t see, the WR star will appear to be brighter than it should for its spectral type and real distance, causing the distance to be misestimated.

The team includes Wallace; Dr. Douglas R. Gies of the Department of Physics and Astronomy, Georgia State University, Atlanta, Ga.; Anthony F. J. Moffat, D?partement de Physique, Universit? de Montr?al, Quebec, Canada; and Michael M. Shara, Department of Astrophysics, American Museum of Natural History, New York, N.Y. The research was funded by NASA.

Original Source: NASA News Release

Image credit: University of Florida

A team of astronomers from the University of Florida have found what could be the brightest star ever seen in the Universe. Located 45,000 light years away across our galaxy, LBV 1806-20 could be 40 million times brighter and 150 times larger than our own Sun. This gigantic and bright star isn’t long for the Universe; however, it’s only a couple of million years old, and will blow up as a supernova in a few million more. This star defies current theories about how large stars should be able to get.

A University of Florida-led team of astronomers may have discovered the brightest star yet observed in the universe, a fiery behemoth that could be as much as much as seven times brighter than the current record holder.

But don?t expect to find the star — which is at least 5 million times brighter than the sun — in the night sky. Dust particles between Earth and the star block out all of its visible light. Whereas the sun is located only 8.3 light minutes from Earth, the bright star is 45,000 light years away, on the other side of the galaxy. It is detectable only with instruments that measure infrared light, which has longer wavelengths that can better penetrate the dust.

In a National Science Foundation-funded study scheduled to be presented today at the American Astronomical Society national conference in Atlanta, the team says the star is at least as bright as the Pistol Star, the current record holder, so named for the pistol-shaped nebula surrounding it. Whereas the Pistol Star is between 5 million and 6 million times as bright as the sun, however, the new contender, LBV 1806-20, could be as much as 40 million times the sun?s brightness.

?We think we?ve found what may be the most massive and most luminous star ever discovered,? said Steve Eikenberry, a UF professor of astronomy and the lead author of a paper on the discovery that was recently submitted to the Astrophysical Journal.

Eikenberry will discuss his findings in a news conference to be held by the society at 12:30 p.m. today at the Courtland Room in the Hyatt Regency Atlanta, where the conference is being held.

One longstanding problem with gauging the brightness of stars at great distances is that what seems at first to be one amazingly bright star turns out on closer examination to be a cluster of nearby stars. Don Figer, an astronomer at the Baltimore-based Space Telescope Science Institute who led the team that discovered the Pistol Star in 1997, said the high-quality data collected by the UF-led team reduced but did not eliminate this possibility.

?The high-resolution data prove that the object is not simply a cluster of lower mass stars, although it is possible that it is a collection of a few stars in a tight orbit around each other,? Figer said. ?More study will be needed to determine the distance and singularity of the object in order to establish whether the object is truly the most massive star known.?

Astronomers have known about LBV 1806-20 since the 1990s. At that time, it was identified as a ?luminous blue variable star? – a relatively rare, massive and short-lived star. Such stars get their names from their propensity to display light and color variability in the infrared spectrum.

Luminous blue variable stars are extremely large, with LBV 1806-20 probably at least 150 times larger than the sun, Eikenberry said. The stars are also extremely young by stellar time. LBV 1806-20 is estimated at less than 2 million years old. The sun in our solar system, by contrast, is 5 billion years old. Typical stars, such as the sun, live 10 billion years.

LBVs have ?short and troubled lives,? as Eikenberry put it, because ?the more mass you have, the more nuclear fuel you have, the faster you burn it up. They start blowing themselves to bits.?

Eikenberry?s team made several key advances that led to the estimate of the star?s oversized mass and brightness, he said.

One, they sharpened infrared images obtained from the Palomar 200-inch telescope at the California Institute of Technology?s Palomar Observatory using a camera equipped with ?speckle imaging,? a relatively new technology for improving resolution of objects at great distances.

?The shimmering that you see coming off a hot blacktop road in the summer – the upper atmosphere kind of does that with star light,? Eikenberry said. ?Speckle imaging kind of freezes that motion out, and you get much better images.?

Composed of 17 astronomers and graduate students, the team also came up with an accurate estimate for the distance from the Earth to the bright star. Team members further determined its temperature and how much of the star?s infrared light gets absorbed by dust particles as the light makes its way toward Earth. The scientists relied on data collected by the Blanco 4-meter telescope at the National Optical Astronomy Observatory?s Cerro Tololo Inter-American Observatory in Chile.

Each of these variables contributed to the estimate of the star?s remarkable candlepower. ?You correct for dust absorption, then you correct for temperature of the star, you correct for distance of the star – all of those things feed into luminosity,? Eikenberry said.

One of the mysteries about LBV 1806-20 is how it got so big. Current theories of star formation suggest they should be limited to about 120 solar masses, or 120 times as large as the sun, because the heat and pressure from such big stars? cores force matter away from their surfaces. Eikenberry said one possibility is that the big star was formed in a process called shock-induced star formation, which occurs when a supernova blows up and slams the gaseous material in a molecular cloud together into a massive star.

The star?s size is not its only distinguishing characteristic. It is located in a small cluster of highly unusual or extremely rare stars, including a so-called ?soft gamma ray repeater,? a freakishly magnetic neutron star that is one of only four identified in the entire galaxy of 100 billion stars. With a magnetic field hundreds of trillions of times more powerful than Earth?s magnetic field, this type of star gets its name from its periodic bursts of gamma rays. The cluster also apparently includes an infant or newly formed star.

?We?ve got this zoo of freak stars, all crammed together, really nearby, and they?re all part of the same cluster of stars,? Eikenberry said. ?It?s really kind of weird.?

Also buried within the cluster is an extremely young infant star, Eikenberry said. The presence of the infant star, the luminous blue variable and the soft gamma ray repeater are vivid examples of an important emerging fact about stellar evolution: All stars in a single cluster don?t form at the same time, he said. ?We?re seeing what I think is going to become a textbook example of the fact that stars aren?t all born in an instant, even in a small cluster,? he said.

Figer, the Pistol Star discoverer, said the research makes an important contribution to astronomers? understanding of the star formation process.

?The findings are significant because such massive stars are very rare and define the upper limits of the star formation process,? he said. ?The team has made a remarkable contribution to our understanding of the most extreme stars.?

The team carrying out this work also included UF?s Jessica LaVine; Keith Matthews, with the California Institute of Technology; Stephane Corbel, with the Universite de Paris; John-David Smith, with the University of Arizona; John Wilson, with the University of Virginia; Donald Barry, Michael Colonno and James Houck, all with Cornell University; and undergraduate research students Shannon Patel, Malia Jackson, and Dounan Hu of Cornell University; and Megan Garske of Northwestern Nazarene University.

Original Source: University of Florida News Release

Image credit: PPARC

Until now, astronomers haven’t been able to find a lot of data about what happened at an early phase in the evolution of the Universe, when it’s thought that the stars were formed. But new research, performed by astronomers using the Gemini observatory in Chile, has revealed several galaxies 8 to 11 billion years ago which are more fully formed than expected. They thought they would see protogalaxies crashing into each other, but instead they found very mature galaxies. Its possible that black holes were much more common in the early Universe and served as anchors to form galaxies rapidly.

Until now, astronomers have been nearly blind when looking back in time to survey an era when most stars in the Universe were expected to have formed. This critical cosmological blind-spot has been removed by a team, including a UK scientist, using the Frederick C. Gillett Gemini North Telescope, showing that many galaxies in the young Universe are not behaving as expected some 8-11 billion years ago.

The surprise: these galaxies appear to be more fully formed and mature than expected at this early stage in the evolution of the Universe. This finding is similar to a teacher walking into a classroom expecting to greet a room full of unruly teenagers and finding well-groomed young adults.

“Theory tells us that this epoch should be dominated by little galaxies crashing together,” said Dr. Roberto Abraham (University of Toronto) who is a Co-Principal Investigator of the team conducting the observations at Gemini. “We are seeing that a large fraction of the stars in the Universe are already in place when the Universe was quite young, which should not be the case. This glimpse back in time shows pretty clearly that we need to re-think what happened during this early epoch in galactic evolution. The theoreticians will definitely have something to gnaw on!”

The results were announced today at the 203rd meeting of the American Astronomical Society in Atlanta, Georgia. The data will soon be released to the entire astronomical community for further analysis, and four papers are nearing completion for publication in The Astrophysical Journal and The Astronomical Journal.

Dr Isobel Hook, leader of the UK Gemini Support Group, based at Oxford University, is a member of the multinational Gemini Deep Deep Survey (GDDS) team who undertook the investigation. She explains how the technique works, The team used a special technique to capture the faintest galactic light ever dissected into the rainbow of colours called a spectrum. In all, spectra from over 300 galaxies were collected, most of which are within what is called the “Redshift Desert,” a relatively unexplored period of the Universe seen by telescopes looking back to an era when the universe was only 3-6 billion years old.

She adds, These spectra represent the most complete sample ever obtained of galaxies in the Redshift Desert. By obtaining large amounts of data from four widely separated fields, this survey provides the statistical basis for drawing conclusions that have been suspected by past observations done by the Hubble Space Telescope, Keck Observatory, Subaru Telescope and the Very Large Telescope over the past decade.

Studying the faint galaxies at this epoch when the Universe was only 20-40% of its current age presents a daunting challenge to astronomers, even when using the light-gathering capacity of a very large telescope like Gemini North with its 8-metre mirror. All previous galaxy surveys in this realm have focused on galaxies where intense star formation is occurring, which makes it easier to obtain spectra but produces a biased sample. The GDDS was able to select a more representative sample including those galaxies which hold the most starsnormal, dimmer, and more massive galaxiesthat demand special techniques to coax a spectrum from their dim light.

“The Gemini data is the most comprehensive survey ever done covering the bulk of the galaxies that represent conditions in the early Universe. These are the massive galaxies that are actually more difficult to study because of their lack of energetic light from star formation. These highly developed galaxies, whose star-forming youth is in fact long gone, just shouldn’t be there, but are,” said Co-Principal Investigator Dr. Karl Glazebrook (Johns Hopkins University).

Astronomers trying to understand this issue might have to put everything on the table. “It is unclear if we need to tweak the existing models or develop a new one in order to understand this finding,” said the survey’s third Co-Principal Investigator, Dr. Patrick McCarthy (Observatories of the Carnegie Institution). “It is quite obvious from the Gemini spectra that these are indeed very mature galaxies, and we are not seeing the effects of obscuring dust. Obviously there are some major aspects about the early lives of galaxies that we just don’t understand. It is even possible that black holes might have been much more ubiquitous than we thought in the early Universe and played a larger role in seeding early galaxy formation.”

What is arguably the dominant galactic evolution theory postulates that the population of galaxies at this early stage should have been dominated by evolutionary building blocks. Aptly called the Hierarchical Model, it predicts that normal to large galaxies, like those studied in this work, would not yet exist and would instead be forming from local beehives of activity where big galaxies grew. The GDDS reveals that this might not be the case.

The spectra from this survey were also used to determine the pollution of the interstellar gas by heavy elements (called “metals”) produced by stars. This is a key indicator of the history of stellar evolution in galaxies. Sandra Savaglio (Johns Hopkins University), who studied this aspect of the research said, “Our interpretation of the Universe is strongly affected by the way we observe it. Because the GDDS observed very weak galaxies, we could detect the interstellar gas even if partly obscured by the presence of dust. Studying the chemical composition of the interstellar gas, we discovered that the galaxies in our survey are more metal-rich than expected.”

Caltech astronomer, Dr. Richard Ellis commented, “The Gemini Deep Deep Survey represents a very significant achievement, both technically and scientifically. The survey has provided a new and valuable census of galaxies during a key period in cosmic history, one that has been difficult to study until now, particularly for the quiescent component of the galaxy population.”

Making observations in the Redshift Desert has frustrated modern astronomers for the last decade. While astronomers have known that plenty of galaxies must exist in the Redshift Desert, it is only a “desert” because we couldn’t get good spectra from many of them. The problem lies in the fact that key spectroscopic features used to study these galaxies have been redshifteddue to the expansion of the Universeinto a part of the optical spectrum that corresponds to a faint, natural, obscuring glow in the Earth’s night time atmosphere.

To overcome this problem, a sophisticated technique called “Nod and Shuffle” was used on the Gemini telescope. “The Nod and Shuffle technique enables us to skim off the faint natural glow of the night sky to reveal the tenuous spectra of galaxies beneath it. These galaxies are over 300 times fainter than this sky glow,” explains Dr. Kathy Roth, an astronomer at Gemini who was also part of the team and obtained much of the data. “It has proven to be an extremely effective way to radically reduce the “noise” or contamination levels that are found in the signal from an electronic light detector.”

Each observation lasted the equivalent of about 30 hours and produced nearly 100 spectra simultaneously. The entire project required over 120 total hours of telescope time. “This is a lot of valuable time on the sky, but when you consider that it has allowed us to help fill in a crucial 20% gap in our understanding of the Universe, it was time well spent,” adds Dr. Glazebrook who developed the use of Nod and Shuffle with Joss Hawthorn for faint galaxy observations while at the Anglo-Australian Observatory a few years ago.

Previous studies in the Redshift Desert have concentrated on galaxies that were not necessarily representative of mainstream systems. For this study, galaxies were carefully selected based upon data from the Las Campanas Infrared Survey in order to assure that strong ultraviolet emitting starburst galaxies were not oversampled. “This study is unique in that we were able to study the red end of the spectrum, and this tells us about the ages of old stars,” says Dr. Abraham. “We undertook incredibly long exposures with Geminiabout ten times as long as typical exposures. This let us look at much fainter galaxies than is usually the case, and let us focus on the bulk of the stars, instead of just the flashy young ones. This makes it a lot easier for us to work out how the galaxies are evolving. We are no longer guessing at it by studying young objects and assuming the old objects were not contributing much to the story of galaxy evolution. It turns out that there are lots of old galaxies out there, but they’re really hard to find.”

Original Source: PPARC News Release

Image credit: SDSS

Gravitational lensing happens when the light from a distant object, such as a quasar, is distorted by the gravity of a closer object. Astronomers have discovered just such a lens, where the distortions are so great, they have to be caused by a significant amount of dark matter – the visible material alone couldn’t be responsible. Dark matter is predicted by its gravitational influence on galaxies and stars in the Universe, but so far, astronomers aren’t really sure what it is; whether it’s just regular matter which is too cold to be seen from Earth, or some kind of exotic particle.

Sloan Digital Sky Survey scientists have discovered a gravitationally lensed quasar with the largest separation ever recorded, and, contrary to expectations, found that four of the most distant, most luminous quasars known are not gravitationally lensed.

Albert Einstein’s Theory of General Relativity predicts that the gravitational pull of a massive body can act as a lens, bending and distorting the light of a distant object. A massive structure somewhere between a distant quasar and Earth can “lens” the light of a quasar, making the image substantially brighter and producing several images of one object.

In a paper published in the December 18/25 edition of NATURE magazine, a Sloan Digital Sky Survey (SDSS) team led by University of Tokyo graduate students Naohisa Inada and Masamune Oguri report that four quasars in close proximity are, in fact, the light from one quasar split into four images by gravitational lensing.

More than 80 gravitationally lensed quasars have been discovered since the first example was found in 1979. A dozen of the cataloged lensed quasars are SDSS discoveries, of which half are the result of the work of Inada and his team.

But what makes this latest finding so dramatic is that the separation between the four images is twice as large as that of any previously known gravitationally lensed quasar. Until the discovery of this quadruple lens quasar, the largest separation known in a gravitationally lensed quasar was 7 arcseconds. The quasar found by the SDSS team lies in the constellation Leo Minor; it consists of four images separated by 14.62 arcseconds.

In order to produce such a large separation, the concentration of matter giving rise to the lensing has to be particularly high. There is a cluster of galaxies in the foreground of this gravitational lens; the dark matter associated with the cluster must be responsible for the unprecedented large separation.

“Additional observations obtained at the Subaru 8.2 meter telescope and Keck telescope confirmed that this system is indeed a gravitational lens,” explains Inada. “Quasars split this much by gravitational lensing are predicted to be very rare, and thus can only be discovered in very large surveys like the SDSS.”

Oguri added: “Discovering one such wide gravitational lens out of over 30,000 SDSS quasars surveyed to date is perfectly consistent with theoretical expectations of models in which the universe is dominated by cold dark matter. This offers additional strong evidence for such models.” (Cold dark matter, unlike hot dark matter, forms tight clumps, the kind that causes this kind of gravitational lens.)

“The gravitational lens we have discovered will provide an ideal laboratory to explore the relation between visible objects and invisible dark matter in the universe,” Oguri explained.

In a second paper to be published in the Astronomical Journal in March 2004, a team led by Gordon Richards of Princeton University used the high resolution of the Hubble Space Telescope to examine four of the most distant known quasars discovered by SDSS for signs of gravitational lensing.

Looking to great distances in astronomy is looking back in time. These quasars are seen at a time when the universe was less than 10percent of its present age. These quasars are tremendously luminous, and are thought to be powered by enormous black holes with masses several billion times that of the Sun. The researchers said it is a real mystery how such massive black holes could have formed so early in the universe. Yet if these objects are gravitationally lensed, SDSS researchers would infer substantially smaller luminosities and therefore black hole masses, making it easier to explain their formation.

“The more distant a quasar, the more likely a galaxy lies between it and the viewer. This is why we expected the most distant quasars to be lensed,” explained SDSS researcher Xiaohui Fan of the University of Arizona. However, contrary to expectations, none of the four shows any sign of multiple images that is the hallmark of lensing.

“Only a small fraction of quasars are gravitationally lensed. However, quasars this bright are very rare in the distant universe. Since lensing causes quasars to appear brighter and therefore easier to detect, we expected that our distant quasars were the ones most likely to be lensed,” suggested team member Zoltan Haiman of Columbia University.

“The fact that these quasars are not lensed says that astronomers have to take seriously the idea that quasars a few billion times the mass of the Sun formed less than a billion years after the Big Bang”, said Richards. “We’re now looking for more examples of high-redshift quasars in the SDSS to give theorists even more supermassive black holes to explain.”

Original Source: SDSS News Release

Image credit: ESO

The European Southern Observatory has released three new images of distant spiral galaxies, which were taken while astronomers were searching for quasars. NGC 613 is a beautiful barred spiral galaxy in the southern constellation of Sculptor; NGC 1792 is a starburst spiral galaxy located in the southern constellation of Columba; and NGC 3627 is also known as Messier 66 and located in the constellation Leo.

Not so long ago, the real nature of the “spiral nebulae”, spiral-shaped objects observed in the sky through telescopes, was still unknown. This long-standing issue was finally settled in 1924 when the famous American astronomer Edwin Hubble provided conclusive evidence that they are located outside our own galaxy and are in fact “island universes” of their own.

Nowadays, we know that the Milky Way is just one of billions of galaxies in the Universe. They come in vastly different shapes – spiral, elliptical, irregular – and many of them are simply beautiful, especially the spiral ones.

Astronomers Mark Neeser from the Universit?ts-Sternwarte M?nchen (Germany) and Peter Barthel from the Kapteyn Institute in Groningen (The Netherlands) were clearly not insensitive to this when they obtained images of three beautiful spiral galaxies with ESO’s Very Large Telescope (VLT). They did this in twilight during the early morning when they had to stop their normal observing programme, searching for very distant and faint quasars.

The resulting colour images (ESO PR Photos 33a-c/03) were produced by combining several CCD images in three different wavebands from the FORS multi-mode instruments.

The three galaxies are known as NGC 613, NGC 1792 and NGC 3627. They are characterized by strong far-infrared, as well as radio emission, indicative of substantial ongoing star-formation activity. Indeed, these images all display prominent dust as well as features related to young stars, clear signs of intensive star-formation.

NGC 613
NGC 613 is a beautiful barred spiral galaxy in the southern constellation Sculptor. This galaxy is inclined by 32 degrees and, contrary to most barred spirals, has many arms that give it a tentacular appearance.

Prominent dust lanes are visible along the large-scale bar. Extensive star-formation occurs in this area, at the ends of the bar, and also in the nuclear regions of the galaxy. The gas at the centre, as well as the radio properties are indicative of the presence of a massive black hole in the centre of NGC 613.

NGC 1792
NGC 1792 is located in the southern constellation Columba (The Dove) – almost on the border with the constellation Caelum (The Graving Tool) – and is a so-called starburst spiral galaxy. Its optical appearance is quite chaotic, due to the patchy distribution of dust throughout the disc of this galaxy. It is very rich in neutral hydrogen gas – fuel for the formation of new stars – and is indeed rapidly forming such stars. The galaxy is characterized by unusually luminous far-infrared radiation; this is due to dust heated by young stars.

M 66 (NGC 3627)
The third galaxy is NGC 3627, also known as Messier 66, i.e. it is the 66th object in the famous catalogue of nebulae by French astronomer Charles Messier (1730 – 1817). It is located in the constellation Leo (The Lion).

NGC 3627 is a beautiful spiral with a well-developed central bulge. It also displays large-scale dust lanes. Many regions of warm hydrogen gas are seen throughout the disc of this galaxy. The latter regions are being ionised by radiation from clusters of newborn stars. Very active star-formation is most likely also occurring in the nuclear regions of NGC 3627.

The galaxy forms, together with its neighbours M 65 and NGC 3628, the so-called “Leo Triplet”; they are located at a distance of about 35 million light-years. M 66 is the largest of the three. Its spiral arms appear distorted and displaced above the main plane of the galaxy. The asymmetric appearance is most likely due to gravitational interaction with its neighbours.

Original Source: ESO News Release

Image credit: ESO

Although the Universe is currently a beige colour overall, it used to be more blue, according to astronomers with the European Southern Observatory. This was caused by the predominantly hot, young blue stars in the most distant galaxies – astronomers are seeing them when the Universe was only 2.5 billion years old. The astronomers worked out the distance and colour to 300 galaxies which were contained within the Hubble Deep Sky survey, which took a deep look at a region of sky in the southern constellation of Tuscanae.

An international team of astronomers [1] has determined the colour of the Universe when it was very young. While the Universe is now kind of beige, it was much bluer in the distant past, at a time when it was only 2,500 million years old.

This is the outcome of an extensive and thorough analysis of more than 300 galaxies seen within a small southern sky area, the so-called Hubble Deep Field South. The main goal of this advanced study was to understand how the stellar content of the Universe was assembled and has changed over time.

Dutch astronomer Marijn Franx, a team member from the Leiden Observatory (The Netherlands), explains: “The blue colour of the early Universe is caused by the predominantly blue light from young stars in the galaxies. The redder colour of the Universe today is caused by the relatively larger number of older, redder stars.”

The team leader, Gregory Rudnick from the Max-Planck Institut f?r Astrophysics (Garching, Germany) adds: “Since the total amount of light in the Universe in the past was about the same as today and a young blue star emits much more light than an old red star, there must have been significantly fewer stars in the young Universe than there is now. Our new findings imply that the majority of stars in the Universe were formed comparatively late, not so long before our Sun was born, at a moment when the Universe was around 7,000 million years old.”

These new results are based on unique data collected during more than 100 hours of observations with the ISAAC multi-mode instrument at ESO’s Very Large Telescope (VLT), as part of a major research project, the Faint InfraRed Extragalactic Survey (FIRES). The distances to the galaxies were estimated from their brightness in different optical near-infrared wavelength bands.

Observing the early Universe
It is now well known that the Sun was formed some 4.5 billion years ago. But when did most of the other stars in our home Galaxy form? And what about stars in other galaxies? These are some of the key questions in present-day astronomy, but they can only be answered by means of observations with the world’s largest telescopes.

One way to address these issues is to observe the very young Universe directly – by looking back in time. For this, astronomers take advantage of the fact that light emitted by very distant galaxies travels a long time before reaching us. Thus, when astronomers look at such remote objects, they see them as they appeared long ago.

Those remote galaxies are extremely faint, however, and these observations are therefore technically difficult. Another complication is that, due to the expansion of the Universe, light from those galaxies is shifted towards longer wavelengths [2], out of the optical wavelength range and into the infrared region.

In order to study those early galaxies in some detail, astronomers must therefore use the largest ground-based telescopes, collecting their faint light during very long exposures. In addition they must use infrared-sensitive detectors.

Telescopes as giant eyes
The “Hubble Deep Field South (HDF-S)” is a very small portion of the sky in the southern constellation Tucanae (“the Toucan”). It was selected for very detailed studies with the Hubble Space Telescope (HST) and other powerful telescopes. Optical images of this field obtained by the HST represent a total exposure time of 140 hours. Many ground-based telescopes have also obtained images and spectra of objects in this sky area, in particular the ESO telescopes in Chile.

A sky area of 2.5 x 2.5 arcmin2 in the direction of HDF-S was observed in the context of a thorough study (the Faint InfraRed Extragalactic Survey; FIRES, see ESO PR 23/02). It is slightly larger than the field covered by the WFPC2 camera on the HST, but still 100 times smaller than the area subtended by the full moon.

Whenever this field was visible from the ESO Paranal Observatory and the atmospheric conditions were optimal, ESO astronomers pointed the 8.2-m VLT ANTU telescope in this direction, taking near-infrared images with the ISAAC multi-mode instrument. Altogether, the field was observed for more than 100 hours and the resulting images (see ESO PR 23/02), are the deepest ground-based views in the near-infrared Js- and H-bands. The Ks-band image is the deepest ever obtained of any sky field in this spectral band, whether from the ground or from space.

These unique data provide an exceptional view and have now allowed unprecedented studies of the galaxy population in the young Universe. Indeed, because of the exceptional seeing conditions at Paranal, the data obtained with the VLT have an excellent image sharpness (a “seeing” of 0.48 arcsec) and can be combined with the HST optical data with almost no loss of quality.

A bluer colour
The astronomers were able to detect unambiguously about 300 galaxies on these images. For each of them, they measured the distance by determining the redshift [2]. This was done by means of a newly improved method that is based on the comparison of the brightness of each object in all the individual spectral bands with that of a set of nearby galaxies.

In this way, galaxies were found in the field with redshifts as high as z = 3.2, corresponding to distances around 11,500 million light-years. In other words, the astronomers were seeing the light of these very remote galaxies as they were when the Universe was only about 2.2 billion year old.

The astronomers next determined the amount of light emitted by each galaxy in such a way that the effects of the redshift were “removed”. That is, they measured the amount of light at different wavelengths (colours) as it would have been recorded by an observer near that galaxy. This, of course, only refers to the light from stars that are not heavily obscured by dust.

Summing up the light emitted at different wavelengths by all galaxies at a given cosmic epoch, the astronomers could then also determine the average colour of the Universe (the “cosmic colour”) at that epoch. Moreover, they were able to measure how that colour has changed, as the Universe became older.

They conclude that the cosmic colour is getting redder with time. In particular, it was much bluer in the past; now, at the age of nearly 14,000 million years, the Universe has a kind of beige colour.

When did stars form ?
The change of the cosmic colour with time may be interesting in itself, but it is also an essential tool for determining how rapidly stars were assembled in the Universe.

Indeed, while the star-formation in individual galaxies may have complicated histories, sometimes accelerating into true “star-bursts”, the new observations – now based on many galaxies – show that the “average history” of star-formation in the Universe is much simpler. This is evident by the observed, smooth change of the cosmic colour as the Universe became older.

Using the cosmic colour the astronomers were also able to determine how the mean age of relatively unobscured stars in the Universe changed with time. Since the Universe was much bluer in the past than it is now, they concluded that the Universe is not producing as many blue (high mass, short-lived) stars now as it was earlier, while at the same time the red (low mass, long-lived) stars from earlier generations of star formation are still present. Blue, massive stars die more quickly than red, low-mass stars, and therefore as the age of a group of stars increases, the blue short-lived stars die and the average colour of the group becomes redder. So did the Universe as a whole.

This behaviour bears some resemblance with the ageing trend in modern Western countries where less babies are born than in the past and people live longer than in the past, with the total effect that the mean age of the population is rising.

The astronomers determined how many stars had already formed when the Universe was only about 3,000 million years old. Young stars (of blue colour) emit more light than older (redder) stars. However, since there was just about as much light in the young Universe as there is today – although the galaxies are now much redder – this implies that there were fewer stars in the early Universe than today. The present study inidcates that there were ten times fewer stars at that early time than there is now.

Finally, the astronomers found that roughly half of the stars in the observed galaxies have been formed after the time when the Universe was about half as old (7,000 million years after the Big Bang) as it is today (14,000 million years).

Although this result was derived from a study of a very small sky field, and therefore may not be completely representative of the Universe as a whole, the present result has been shown to hold in other sky fields.

Original Source: ESO News Release

Image credit: NASA

NASA’s Stardust spacecraft has nearly arrived at its first destination, Comet Wild 2. On January 2, 2004, the spacecraft will buzz through the comet’s tail and collect interstellar particles and dust. The particles will be captured on a tennis racket-shaped grid that will ensure they aren’t damaged. Stardust will return the sample to Earth in 2006 so that scientists can analyze it on the ground. It’s believed that comets are as old as the solar system, so analyzing these particles will reveal valuable information about our origins.

On January 2nd 2004 the NASA space mission, STARDUST, will fly through comet Wild 2, capturing interstellar particles and dust and returning them to Earth in 2006. Space scientists from the Open University and University of Kent have developed one of the instruments which will help tell us more about comets and the evolution of our own solar system and, critical for STARDUST, its survival in the close fly-by of the comet.

Launched in February 1999, STARDUST is the first mission designed to bring samples back from a known comet. The study of comets provides a window into the past as they are the best preserved raw materials in the Solar System. The cometary and interstellar dust samples collected will help provide answers to fundamental questions about the origins of the solar system.

Scientists from the Open University and University of Kent have developed one set of sensors for the Dust Flux Monitor Instrument (DFMI) built by the University of Chicago, and the software to analyse the data. The DFMI, part funded by the Particle Physics and Astronomy Research Council (PPARC) will record the distribution and sizes of particles on its journey through the centre, or coma, of the comet.

Professor Tony McDonnell and Dr Simon Green from the Open Universitys Planetary and Space Science Research Institute (PSSRI), will be at the mission command centre, the Jet Propulsion Laboratory in California, when the encounter with Wild 2 begins.

Dr Green explains By combining the information about each of the tiny grains of dust captured by STARDUST we will discover more about the formation of stars, planets and our solar system.

Professor Tony McDonnell said The information derived from the signals will tell us on the night if the dust shield has been critically punctured.

Cometary particles will be captured on a tennis racket like grid which contains a substance called aerogel the lightest solid in the Universe! This is a porous material that allows the particles to become embedded with minimum damage. This means that on their return to Earth they will be as near as possible to their original state.

Once the samples are captured a clam-like shell closes around them. The capsule then returns to Earth in January 2006 where it will land at the US Air Force Utah Test and Training Range. Once collected, the samples will be taken to the planetary material curatorial facility at NASAs Johnson Space Centre, Houston, where they will be carefully stored and examined.

The Open University team hope to be involved in analysing the samples that return to Earth in January 2006.

UK scientists, including a team from the Open University, are also involved with the European Space Agencys Rosetta Mission which will follow and land on Comet Churyumov-Gerasimenko. This mission is due to be launched on 26th February 2004.

Original Source: PPARC News Release

Image credit: ESA

It was only a few years ago that astronomers shook up current models of the Universe with the theory of dark energy; which says that the expansion of the Universe is actually accelerating. But new evidence gathered by the ESA’s XMM-Newton X-ray observatory has cast some doubt on the theory. By looking at distant galaxy clusters – up to 10 billion light-years away – the ESA astronomers found they contained more concentrated matter than the theory of dark energy would predict. If matter was so concentrated, the Universe can’t be 70% dark energy.

ESA’s X-ray observatory, XMM-Newton, has returned tantalising new data about the nature of the Universe. In a survey of distant clusters of galaxies, XMM-Newton has found puzzling differences between today’s clusters of galaxies and those present in the Universe around seven thousand million years ago. Some scientists claim that this can be interpreted to mean that the ‘dark energy’ which most astronomers now believe dominates the Universe simply does not exist?

Observations of eight distant clusters of galaxies, the furthest of which is around 10 thousand million light years away, were studied by an international group of astronomers led by David Lumb of ESA’s Space Research and Technology Centre (ESTEC) in the Netherlands. They compared these clusters to those found in the nearby Universe. This study was conducted as part of the larger XMM-Newton Omega Project, which investigates the density of matter in the Universe under the lead of Jim Bartlett of the College de France.

Clusters of galaxies are prodigious emitters of X-rays because they contain a large quantity of high-temperature gas. This gas surrounds galaxies in the same way as steam surrounds people in a sauna. By measuring the quantity and energy of X-rays from a cluster, astronomers can work out both the temperature of the cluster gas and also the mass of the cluster.

Theoretically, in a Universe where the density of matter is high, clusters of galaxies would continue to grow with time and so, on average, should contain more mass now than in the past.

Most astronomers believe that we live in a low-density Universe in which a mysterious substance known as ‘dark energy’ accounts for 70% of the content of the cosmos and, therefore, pervades everything. In this scenario, clusters of galaxies should stop growing early in the history of the Universe and look virtually indistinguishable from those of today.

In a paper soon to be published by the European journal Astronomy and Astrophysics, astronomers from the XMM-Newton Omega Project present results showing that clusters of galaxies in the distant Universe are not like those of today. They seem to give out more X-rays than today. So clearly, clusters of galaxies have changed their appearance with time.

In an accompanying paper, Alain Blanchard of the Laboratoire d’Astrophysique de l’Observatoire Midi-Pyr?n?es and his team use the results to calculate how the abundance of galaxy clusters changes with time. Blanchard says, “There were fewer galaxy clusters in the past.”

Such a result indicates that the Universe must be a high-density environment, in clear contradiction to the ‘concordance model,’ which postulates a Universe with up to 70% dark energy and a very low density of matter. Blanchard knows that this conclusion will be highly controversial, saying, “To account for these results you have to have a lot of matter in the Universe and that leaves little room for dark energy.”

To reconcile the new XMM-Newton observations with the concordance models, astronomers would have to admit a fundamental gap in their knowledge about the behaviour of the clusters and, possibly, of the galaxies within them. For instance, galaxies in the faraway clusters would have to be injecting more energy into their surrounding gas than is currently understood. That process should then gradually taper off as the cluster and the galaxies within it grow older.

No matter which way the results are interpreted, XMM-Newton has given astronomers a new insight into the Universe and a new mystery to puzzle over. As for the possibility that the XMM-Newton results are simply wrong, they are in the process of being confirmed by other X-ray observations. Should these return the same answer, we might have to rethink our understanding of the Universe.

The contents of the Universe
The content of the Universe is widely thought to consist of three types of substance: normal matter, dark matter and dark energy. Normal matter consists of the atoms that make up stars, planets, human beings and every other visible object in the Universe. As humbling as it sounds, normal matter almost certainly accounts for a small proportion of the Universe, somewhere between 1% and 10%.

The more astronomers observed the Universe, the more matter they needed to find to explain it all. This matter could not be made of normal atoms, however, otherwise there would be more stars and galaxies to be seen. Instead, they coined the term dark matter for this peculiar substance precisely because it escapes our detection. At the same time, physicists trying to further the understanding of the forces of nature were starting to believe that new and exotic particles of matter must be abundant in the Universe. These would hardly ever interact with normal matter and many now believe that these particles are the dark matter. At the present time, even though many experiments are underway to detect dark matter particles, none have been successful. Nevertheless, astronomers still believe that somewhere between 30% and 99% of the Universe may consist of dark matter.

Dark energy is the latest addition to the contents of the Universe. Originally, Albert Einstein introduced the idea of an all-pervading ‘cosmic energy’ before he knew that the Universe is expanding. The expanding Universe did not need a ‘cosmological constant’ as Einstein had called his energy. However, in the 1990s observations of exploding stars in the distant Universe suggested that the Universe was not just expanding but accelerating as well. The only way to explain this was to reintroduce Einstein’s cosmic energy in a slightly altered form, called dark energy. No one knows what the dark energy might be.

In the currently popular ‘concordance model’ of the Universe, 70% of the cosmos is thought to be dark energy, 25% dark matter and 5% normal matter.

Original Source: ESA News Release

Image credit: NASA

NASA’s Galaxy Evolution Explorer (GALEX) has captured the most sensitive and comprehensive ultraviolet images ever taken of the Andromeda galaxy, M31. By studying the galaxy in the ultraviolet spectrum, astronomers can study some of the fundamental processes that lead the formation of new stars. A new collection of images included Andromeda, as well as the globular cluster M2, and the sky in the constellation of Bootes. GALEX was launched in April, 2003, and will map the sky in the ultraviolet spectrum, looking back to 10 billion years ago.

The most sensitive and comprehensive ultraviolet image ever taken of the Andromeda Galaxy, our nearest large neighbor galaxy, has been captured by NASA?s Galaxy Evolution Explorer. The image is one of several being released to the public as part of the mission?s first collection of pictures.

“The Andromeda image gives us a snapshot of the most recent star formation episode,” said Dr. Christopher Martin, Galaxy Evolution Explorer principal investigator and an astrophysics professor at the California Institute of Technology in Pasadena, which leads the mission. ?By studying this view of the galaxy in the process of forming stars, we can better understand how that fundamental process works, such as where stars form, how fast and why.?

The image of Andromeda, the most distant object the naked eye can see, is a mosaic of nine images taken in September and October of 2003. It combines two ultraviolet colors, one near ultraviolet (red) and one far ultraviolet (blue).

For comparison, a second image shows the Andromeda Galaxy, also called Messier 31, in visible light. Both images, along with other new pictures from the Galaxy Evolution Explorer, are available online at http://www.galex.caltech.edu and http://photojournal.jpl.nasa.gov/mission/GALEX . The new collection of images also includes views of several nearby galaxies; Stephan’s Quintet of Galaxies; an all-sky survey image of the globular star cluster M2; and a deep image of the sky in the constellation Bootes. The Galaxy Evolution Explorer team is also releasing the first batch of scientific data, so the science community can propose additional observations for the mission. These images and data display the power of the Galaxy Evolution Explorer to collect sensitive ultraviolet images of large parts of the sky.

“It?s very rewarding and exciting for the team to see the fruits of their labors,” said Kerry Erickson, the mission?s project manager at NASA?s Jet Propulsion Laboratory, Pasadena, Calif. ?Because people are accustomed to seeing objects in visible light, it?s amazing to see how different the universe looks in ultraviolet and how much information is revealed to us by those observations.?

Scientists are interested in learning more about the Andromeda galaxy, including its brightness, mass, age, and the distribution of young star clusters in its spiral arms. This will provide a tremendous amount of information about the mechanisms of star formation in galaxies, and will help them interpret ultraviolet and infrared observations of other, more distant galaxies.

The Galaxy Evolution Explorer launched on April 28, 2003. Its goal is to map the celestial sky in the ultraviolet and determine the history of star formation in the universe over the last 10 billion years. From its orbit high above Earth, the spacecraft will sweep the skies for up to 28 months using state-of-the-art ultraviolet detectors. Looking in the ultraviolet singles out galaxies dominated by young, hot, short-lived stars that give off a great deal energy at that wavelength. These galaxies are actively creating stars, and therefore provide a window into the history and causes of galactic star formation.

In addition to leading the mission, Caltech is also responsible for science operations and data analysis. JPL, a division of Caltech, manages the mission and led the science instrument development. The mission is part of NASA’s Explorers Program, managed by the Goddard Space Flight Center, Greenbelt, Md. The mission’s international partners are France and South Korea. Caltech manages JPL for NASA

Original Source: NASA News Release

Image credit: NASA/JPL

New research from the University of Colorado shows how recycling of material can extend the lifetime of a ring system, such as those around Jupiter, Saturn, Neptune and Uranus. The small moons near the gas giants have long been known to sculpt the shape of the rings. It’s now believed that they’re piles of loosely-collected rubble which pull material out of the rings and then feed it back in when they collide with another object. NASA’s Cassini spacecraft is on its way to Saturn now and should provide more details when it arrives in July 2004.

Although rings around planets like Jupiter, Saturn, Uranus and Neptune are relatively short-lived, new evidence implies that the recycling of orbiting debris can lengthen the lifetime of such rings, according to University of Colorado researchers.

Strong evidence now implies small moons near the giant planets like Saturn and Jupiter are essentially piles of rubble, said Larry Esposito, a professor at CU-Boulder’s Laboratory for Atmospheric and Space Physics. These re-constituted small bodies are the source of material for planetary rings.

Previous calculations by Esposito and LASP Research Associate Joshua Colwell showed the short lifetimes for such moons imply that the solar system is nearly at the end of the age of rings. “These philosophically unappealing results may not truly describe our solar system and the rings that may surround giant extra-solar planets,” said Esposito. “Our new calculations of models explain how inclusion of recycling can lengthen the lifetime of rings and moons.”

The observations from the Voyager and Galileo space missions showed a variety of rings surrounding each of the giant planets, including Jupiter, Saturn, Uranus and Neptune. The rings are mixed in each case with small moons.

“It is clear that the small moons not only sculpt the rings through their gravity, but are also the parents of the ring material,” said Esposito. “In each ring system, destructive processes like grinding, darkening and spreading are acting so rapidly that the rings must be much younger than the planets they circle.”

Numerical models by Esposito and Colwell from the 1990’s showed a “collisional cascade,” where a planet’s moons are broken into smaller moons when struck by asteroids or comets. The fragments then are shattered to form the particles in new rings. The rings themselves are subsequently ground to dust, which is swept away.

But according to Colwell, “Some of the fragments that make up the rings may be re-accreted instead of being ground to dust. New evidence shows some debris has accumulated into moons or moonlets rather than disappearing through collisional erosion.”

“This process has proceeded rapidly,” said Esposito. “The typical ring is younger than a few hundred million years, the blink of an eye compared to the planets, which are 4.5 billion years old. The question naturally arises why rings still exist, to be photographed in such glory by visiting human spacecraft that have arrived lately on the scene,” he said.

“The answer now likely seems to be cosmic recycling,” said Esposito. Each time a moon is destroyed by a cosmic impact, much of the material released is captured by other nearby moons. These recycled moons are essentially collections of rubble, but by recycling material through a series of small moons, the lifetime of the ring system may be longer than we initially thought.”

Esposito and former LASP Research Associate Robin Canup, now with the Southwest Research Institute’s Boulder branch, showed through computer modeling that smaller fragments can be recaptured by other moons in the system. “Without this recycling, the rings and moons are soon gone,” said Esposito.

But with more recycling, the lifetime is longer, Esposito said. With most of the material recycled, as now appears to be the case in most rings, the lifetime is extended by a large factor.

“Although the individual rings and moons we now see are ephemeral, the phenomenon persists for billions of years around Saturn,” said Esposito. “Previous calculations ignored the collective effects of the other moons in extending the persistence of rings by recapturing and recycling ring material.”

Esposito, the principal investigator on a $12 million spectrograph on the Cassini spacecraft slated to arrive at Saturn in July 2004, will look closely at the competing processes of destruction and re-capture in Saturn’s F ring to confirm and quantify this explanation. Esposito discovered the F Ring using data from NASA’s Voyager 2 mission to the outer planets launched in 1978.

Original Source: University of Colorado News Release