Tuesday, June 28, 2011

Abell 2744: A Distraught Cluster of Galaxies

"One of the most complicated and dramatic collisions between galaxy clusters ever seen is captured in this new composite image," opens Chandra's article of Abell 2744. Distraught as it is, no-one has ever seen such a complicated group that has formed beautifully into a cluster of beauty. 'Pandora's Cluster,' another name for Abell 2744 was named just that, for "so many different and strange phenomena were unleashed by the collision. Some of these phenomena had never been seen before," Renato Dupke, a member of the Pandora's Cluster team remarks. 

But, what exactly happened to Abell 2744?

Galaxies here make up only 5% of the mass. The rest is gas, that shines because of its heat index (twenty percent). The rest (75 percent) is made from invisible dark matter, which astronomers had to distinguish to find out what really happened.

Using gravitational attraction to distinguish the dark matter so the events of Abell 2744 could be distinguished, astronomers quickly bended light-rays from distant galaxies as they passed though the gravitational fields that were inside the cluster. After doing this to the whole cluster, a series of distorted images were given and by carefully telling how these images were distorted, you can find where the dark matter rests. On another note, why go to all this trouble if NASA's Chandra X-ray Observatory can do it all for you; it can see dark matter. "Abell 2744 seems to have formed from four different clusters involved in a series of collisions over a period of some 350 million years. The complicated and uneven distribution of the different types of matter is extremely unusual and fascinating," Dan Coe, leader of this study, tells us. 

Seeming to the astronomer team, a complex collision separated hot gas from dark matter, now lying apart from each other, as well as the visible galaxies. All this has been seen in just one galaxy cluster, which are by far the largest 'objects' in interstellar space. Rare as it is, a few of these events have been viewed singly in other galaxies, but not all in just one! Peculiar to note, inside the cluster's core, there is a 'bullet,' in which gas of  single cluster collided with another (making Abell 2744 a cluster of galaxy clusters!) and making a shock wave. Dark matter, though passed right through it, despite the fact that most 'ordinary' elements in space would have been repelled. The same happened to 1E 0657-56 (also referred to as the 'bullet cluster,' hence the 'bullet' in the center of the colliding galaxy cluster') as pictured below. Note the same colors that Abell 2744 has. 

To make matters more peculiar, strange discoveries have been made on different regions of Abell 2744. In one part, galaxies and dark matter are very prevalent, but no hot gas is in the vicinity. The Abell astronomer team reasons, "The gas may have been stripped away during the collision, leaving behind no more than a faint trail." On the outskirts of the cluster, there are a few regions that contain lots of dark matter, but no glaxies or not gas. Another feature; a 'ghostly' gas clump, as the team describes, had been ejected, where dark matter precedes. These are just to name a few.
So, Abell 2744, "the most complex and fascinating merger yet found," is a beautiful ornament 3.5 billion light years away, about 5.9 million light years across. Comprised of more than four-thousand single galaxies, much more is to be learned of this unique, galaxy cluster.  

Learn more! Videos from European Southern Observatory (ESO):
This research is presented in a paper entitled “Creation of cosmic structure in the complex galaxy cluster merger Abell 2744”, to appear in Monthly Notices of the Royal Astronomical Society.

The team is composed of J. Merten (Institute for Theoretical Astrophysics, Heidelberg, Germany; INAF-Osservatorio Astronomico di Bologna, Italy), D. Coe (Space Telescope Science Institute, Baltimore, USA), R. Dupke (University of Michigan, USA; Eureka Scientific, USA; National Observatory, Rio de Janeiro, Brazil), R. Massey (University of Edinburgh, Scotland), A. Zitrin (Tel Aviv University, Israel), E.S. Cypriano (University of Sao Paulo, Brazil), N. Okabe (Academia Sinica Institute of Astronomy and Astrophysics, Taiwan), B. Frye (University of San Francisco, USA), F. Braglia (University of British Columbia, Canada), Y. Jimenez-Teja (Instituto de Astrofisica de Andalucia, Granada, Spain), N. Benitez (Instituto de Astrofisica de Andalucia), T. Broadhurst (University of Basque Country, Spain), J. Rhodes (Jet Propulsion Laboratory/Caltech, USA), M. Meneghetti (INAF-Osservatorio Astronomico di Bologna, Italy), L. A. Moustakas (Caltech), L. Sodre Jr. (University of Sao Paulo, Brazil), J. Krick (Spitzer Science Center/IPAC/Caltech, USA) and J. N. Bregman (University of Michigan).

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