Dwarf galaxies can be made with gas leftover from early Universe

February 19, 2009 By Leave a Comment

Washington, Feb 19 (ANI): NASA’s Galaxy Evolution Explorer has identified dwarf galaxies forming out of nothing more than pristine gas likely leftover from the early universe.

Dwarf galaxies are relatively small collections of stars that often orbit around larger galaxies like our Milky Way.

The findings surprised astronomers because most galaxies form in association with a mysterious substance called dark matter or out of gas containing metals.

The infant galaxies spotted by the Galaxy Evolution Explorer are springing up out of gas that lacks both dark matter and metals.

Though never seen before, this new type of dwarf galaxy may be common throughout the more distant and early universe, when pristine gas was more pervasive.

Led by David Thilker of the Henry A. Rowland Department of Physics and Astronomy at The Johns Hopkins University, a team of astronomers spotted the unexpected new galaxies forming inside the Leo Ring, a huge cloud of hydrogen and helium that traces a ragged path around two massive galaxies in the constellation Leo.

The cloud is thought likely to be a primordial object, an ancient remnant of material that has remained relatively unchanged since the very earliest days of the universe.

Identified about 25 years ago by radio waves, the ring cannot be seen in visible light.

According to Thilker, “This intriguing object has been studied for decades with world-class telescopes operating at radio and optical wavelengths. Despite such effort, nothing except the gas was detected. No stars at all, young or old, were found.”

“But, when we looked at the ring with the Galaxy Evolution Explorer, which is remarkably sensitive to ultraviolet light, we saw telltale evidence of recent massive star formation. It was really unexpected. We are witnessing galaxies forming out of a cloud of primordial gas,” he added.

“We speculate that these young stellar complexes are dwarf galaxies, although, as previously shown by radio astronomers, the gaseous clumps forming these galaxies lack dark matter,” said Thilker.

“Almost all other galaxies we know are dominated by dark matter, which acted as a seed for the collection of their luminous components – stars, gas, and dust. What we see occurring in the Leo Ring is a new mode for the formation of dwarf galaxies in material remaining from the much earlier assembly of this galaxy group,” he explained. (ANI)

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Stellar object may have had stars packed together in early Universe

February 13, 2009 By Leave a Comment

London, Feb 13 (ANI): New calculations by scientists have suggested that Ultra Compact Dwarf galaxies (UCDs), a recently discovered class of object, may have had stars packed together a thousand times more closely than in the solar neighborhood.

UCDs were discovered in 1999. Although they are still enormous by everyday standards, at about 60 light years across, they are less than 1/1000th the diameter of our own Galaxy, the Milky Way.

Astronomers believe that UCDs were created when more normal galaxies collided in the early Universe.

But oddly, UCDs clearly have more mass than the light from the stars they contain would imply.

Up to now, exotic dark matter has been suggested to explain this ‘missing mass’, but this is not thought to gather in sufficient quantities within a UCD.

In their research, PhD student Joerg Dabringhausen, Professor Pavel Kroupa of the University of Bonn, and their colleague Dr Holger Baumgardt, present a different explanation.

The astronomers think that at one time, each UCD had an incredibly high density of stars, with perhaps 1 million in each cubic light year of space, compared with the 1 that we see in the region of space around the Sun.

These stars would have been close enough to merge from time to time, creating many much more massive stars in their place.

These more massive stars consume hydrogen (their nuclear fuel) much more rapidly, before ending their lives in violent supernova explosions.

All that then remains is either a superdense neutron star or sometimes a black hole.

So, in today’s UCDs, a good part of their mass is made up of these dark remnants, largely invisible to Earth-based telescopes but fossils of a more dramatic past.

According to Dabringhausen, “Billions of years ago, UCDs must have been extraordinary. To have such a vast number of stars packed closely together is quite unlike anything we see today. An observer on a (hypothetical) planet inside a UCD would have seen a night sky as bright as day on Earth.” (ANI)

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Computer simulation reveals ‘dawn’ of the cosmos

February 11, 2009 By Leave a Comment

Washington, Feb 11 (ANI): Scientists have used a computer simulation to come up with images that show the formation of the first big galaxies in the Universe, which is literally the ‘cosmic dawn’.

The images, produced by scientists at Durham University’s Institute for Computational Cosmology, predict what the very early Universe would have appeared like 500 million years after the Big Bang.

The Cosmic Dawn began as galaxies began to form out of the debris of massive stars which died explosively shortly after the beginning of the Universe.

The Durham calculation predicts where these galaxies appear and how they evolve to the present day, over 13 billion years later.

Gravity produced by dark matter is an essential ingredient in galaxy formation and by studying its effects the scientists eventually hope to learn more about what the substance is.

The work combined a massive simulation showing how structures grow in dark matter with a model showing how normal matter, such as gas, behaves to predict how galaxies grow.

Gas feels the pull of gravity from dark matter and is heated up before cooling by releasing radiation and turning into stars.

The simulation images show which galaxies are forming stars most vigorously at a given time.

Although the galaxies are biggest at the present day, the rate at which they are making new stars has dropped greatly compared with the rate in the early Universe.

The calculations of the Durham team, supported by scientists at the Universidad Catolica in Santiago, Chile, can be tested against new observations reaching back to early stages in the history of the Universe almost one billion years after the Big Bang.

According to lead author, Alvaro Orsi, a research postgraduate in Durham University’s Institute for Computational Cosmology (ICC), “We are effectively looking back in time and by doing so we hope to learn how galaxies like our own were made and to understand more about dark matter.”

“The presence of dark matter is the key to building galaxies. Without dark matter, we wouldn’t be here today,” he said.

“Our research predicts which galaxies are growing through the formation of stars at different times in the history of the Universe and how these relate to the dark matter,” said co-author Dr Carlton Baugh, a Royal Society Research Fellow, in the ICC, at Durham University.

“We give the computer what we think is the recipe for galaxy formation and we see what is produced which is then tested against observations of real galaxies,” he added. (ANI)

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Hubble captures exceptionally deep view of unusual spiral galaxy

February 7, 2009 By Leave a Comment

Washington, Feb 6 (ANI): A spectacular new image captured by the Hubble Space Telescope has revealed an exceptionally deep view of an unusual spiral galaxy.

The image of the galaxy, which is in the Coma Galaxy Cluster, has been created from data taken by the Advanced Camera for Surveys on the NASA/ESA Hubble Space Telescope.

It reveals fine details of the galaxy, NGC 4921, as well as an extraordinary rich background of more remote galaxies stretching back to the early Universe.

The Coma Galaxy Cluster, in the northern constellation of Coma Berenices, the hair of Queen Berenice, is one of the closest very rich collections of galaxies in the nearby Universe.

The cluster, also known as Abell 1656, is about 320 million light-years from Earth and contains more than 1000 members.

The galaxies in rich clusters undergo many interactions and mergers that tend to gradually turn gas-rich spirals into elliptical systems without much active star formation.

As a result, there are far more ellipticals and fewer spirals in the Coma Cluster than are found in quieter corners of the Universe.

NGC 4921 is one of the rare spirals in Coma, and a rather unusual one. It is an example of an “anaemic spiral”, where the normal vigorous star formation that creates a spiral galaxy’s familiar bright arms is much less intense.

As a result, there is just a delicate swirl of dust in a ring around the galaxy, accompanied by some bright young blue stars that are clearly separated out by Hubble’s sharp vision.

Much of the pale spiral structure in the outer parts of the galaxy is unusually smooth and gives the whole galaxy the ghostly look of a vast translucent jellyfish.

The long exposure times and sharp vision of Hubble also allowed it to not just image NGC 4921 in exquisite detail, but also to see far beyond into the distant Universe.

This image was created from 50 separate exposures through a yellow filter and another 30 exposures through a near-infrared filter using the Wide Field Channel of the Advanced Camera for Surveys on Hubble. (ANI)

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Giant ‘stellar factory’ identified in early galaxy

February 7, 2009 By Leave a Comment

London, Feb 5 (ANI): Astronomers have identified a giant star producing region in a galaxy in the very early universe, which is millions of times larger than anything comparable in the Milky Way.

According to a report in New Scientist, the work bolsters the case that massive galaxies formed very quickly, in spectacular bursts of star formation, soon after the big bang.

Regions of intense star formation, called starbursts, span a few light years at most in the Milky Way, and less than a few hundred light years in nearby, bright galaxies such as Arp 220.

But, it has not been clear how large the stellar nurseries were in the early universe.

To find out, researchers led by Fabian Walter of the Max Planck Institute for Astronomy in Heidelberg, Germany, carefully scrutinized a distant galaxy whose light has taken so long to reach Earth that it appears as it was just 870 million years after the big bang.

It is visible at such distances because it hosts a beacon-like quasar, a bright region created by superheated gas falling towards a colossal black hole at the galaxy’s core.

The quasar, called J114816.64+525150.3, is so bright that it overwhelms the surrounding galaxy’s light at visible and near-infrared wavelengths.

But, the galaxy’s gas and warm dust can be detected at radio and far-infrared wavelengths.

Using an array of telescopes in the French Alps, the team measured the galaxy’s ionised carbon, which emits a strong signal at far-infrared wavelengths.

Far-infrared radiation is thought to be a signature of dust that has been heated up by nearby star formation.

The ionised carbon spanned a region at the heart of the galaxy about 5000 light years across. Based on the galaxy’s brightness at far-infrared wavelengths, this starburst region is thought to produce an astounding 1000 Sun-like stars every year.

That is “about 1000 times higher than the star-formation rate of the Milky Way”, said team member Chris Carilli, chief scientist at the National Radio Astronomy Observatory in Socorro, New Mexico.

“It’s forming stars at the maximal rate allowed, on scales that are 106 or 108 times larger in volume than similar regions in the Milky Way. That’s remarkable,” he added.

“The immense scale of the stellar factory is probably due to the fact that there was a lot more gas around in the early universe,” Carilli said.

Matter in the universe was indeed much denser soon after the big bang, since space itself has expanded over time. (ANI)

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