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Thanks to data from ESA’s XMM-Newton X-ray satellite, a team of international scientists found a comet-like ball of gas over a thousand million times the mass of the sun hurling through a distant galaxy cluster over 750 kilometres per second.

This colossal 'ball of fire' is by far the largest object of this kind ever identified.
The gas ball is about three million light years across, or about five thousand million times the size of our solar system. It appears from our perspective as a circular X-ray glow with a comet-like tail nearly half the size of the moon.


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"The size and velocity of this gas ball is truly fantastic. This is likely a massive building block being delivered to one of the largest assembly of galaxies we know" - Dr Alexis Finoguenov, adjunct assistant professor of physics in the Department of Physics at the University of Maryland, Baltimore County (UMBC), and an associated scientist at the Max Planck Institute for Extra-Terrestrial Physics in Garching, Germany.

The gas ball is in a galaxy cluster called Abell 3266, millions of light years from Earth, thus posing absolutely no danger to our solar system. Abell 3266 contains hundreds of galaxies and great amounts of hot gas that is nearly a hundred million degrees. Both the cluster gas and the giant gas ball are held together by the gravitational attraction of unseen dark matter.

"What interests astronomers is not just the size of the gas ball but the role it plays in the formation and evolution of structure in the universe" - Dr Francesco Miniati, who worked on this data at UMBC while visiting from the Swiss Federal Institute of Technology in Zurich, Switzerland.

Abell cluster 3266 is part of the Horologium-Reticulum super-cluster and is one of the most massive galaxy clusters in the southern sky. It is still actively growing in size, as indicated by the gas ball, and will become one of the largest mass concentrations in the nearby universe.

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A comprehensive survey of more than 4,000 elliptical and lenticular galaxies in 93 nearby galaxy clusters has found a curious case of galactic “downsizing.”
Contrary to expectations, the largest, brightest galaxies in the census consist almost exclusively of very old stars, with much of their stellar populations having formed as long ago as 13 billion years. There appears to be very little recent star formation in these galaxies, nor is there strong evidence for recent ingestion of smaller, younger galaxies.

By contrast, the smaller, fainter galaxies studied by the NOAO Fundamental Plane Survey are significantly younger—their stars were formed as little as four billion years ago, according to new results from the survey team to be published in the September 10, 2005, Astrophysical Journal.


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This image of galaxy cluster Abell 3266 was taken using the Gemini Multi-Object Spectrograph (GMOS) instrument on the Gemini South telescope on Cerro Pachón, Chile, in July 2005. The image was obtained by the NOAO Fundamental Plane Survey team as part of follow-up observations in support of their spectroscopic data from Kitt Peak National Observatory and Cerro Tololo Inter-American Observatory.
Abell 3266 is located at a distance of 250 million light-years from Earth. It is one of the most populous galaxy clusters in the nearby universe, and one of 93 clusters that were the subject of an August 2005 NOAO press release. Galaxy clusters contain mostly red elliptical galaxies, as seen in this view of the central region of Abell 3266.



These findings are based on a sample more than five times larger than previous efforts. The results of the survey contrast sharply with conventional hierarchical model of galaxy formation and evolution, where large elliptical galaxies in the nearby universe formed by swallowing smaller galaxies with young stars; this theory predicts that, on average, the stars in the largest elliptical galaxies should be no older than those in the smallest ones.

"This sample probes the largest and richest galaxy clusters in the nearby universe, out to a distance of about a billion light-years from Earth. Our analysis shows that there is a clear relationship between mass and age in these red galaxies, meaning that the stars in the biggest, oldest galaxies that we studied formed early in the history of the Universe. On average, the smaller galaxies have one-tenth the mass of the larger ones, and are only about half their age" - Jenica Nelan, lead author of the study.

"The term ‘downsizing’ essentially means that when the Universe was young, the star formation activity occurred in large galaxies, but as the Universe aged, the ‘action’ stopped in the larger galaxies, even as it continued in smaller galaxies" - Michael Hudson of the University of Waterloo, Ontario, Canada, principal investigator for the NOAO Fundamental Plane Survey.

The new study is based on thousands of spectra obtained by the Fundamental Plane Survey team over dozens of nights at the WIYN 3.5-meter telescope at Kitt Peak National Observatory, southwest of Tucson, AZ, and the National Science Foundation’s Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory, east of La Serena, Chile. With some painstaking work, these spectra can reveal the average age of the stars that make up a galaxy.

"Although we cannot directly see these galaxies as they were in the past, their stars are a kind of ‘fossil record’ that can be used to unearth their histories. It appears that the older galaxies are much less of a ‘melting pot’ than had been thought, and that their star formation activity turned off somehow while they were being put together" - Michael Hudson.

The evolutionary history of elliptical galaxies and lenticular galaxies (which have a central bulge and a disk, but no evidence of spiral arms) is not well understood. Their colours appear to be “redder” than typical spiral galaxies. The largest ellipticals are the reddest of all, but until this work it has not been clear whether this property results primarily from being older in age, as the survey found, or from having a higher proportion of heavy chemical elements (metallicity content).

"These so-called red galaxies contain the bulk of the stellar mass in the nearby universe, but we know little about their formation and evolution. It was thought that all of the red galaxies were made of stars that formed very early, and are now quite old. Our results show that while this is true for the large galaxies, the smaller ones formed their stars comparatively recently in the history of the Universe. We predict that as new surveys look deeper and hence further into the past, they should see fewer faint red galaxies" - Russell Smith, co-author, the University of Waterloo.

Lead author Jenica Nelan completed this work while earning her doctorate at Dartmouth College; she is now an astronomer at Yale University.
Co-authors of this paper include Hudson and Smith of the University of Waterloo; Gary Wegner of Dartmouth College; John R. Lucey, Stephen A. W. Moore, and Stephen J. Quinney of the University of Durham, and Nicholas B. Suntzeff of NOAO’s Cerro Tololo Inter-American Observatory.

The Fundamental Plane Survey is one of 18 projects granted long-term access to observing nights at the telescope of the National Optical Astronomy Observatory (NOAO) under the NOAO Survey Program.

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See here for more information:
www.noao.edu and astro.uwaterloo.ca


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