What puzzles me, why an old elliptical system is emitting so much X-ray radiation. In an elliptical system there is hardly any cold gas left for new stars to be formed (
http://heritage.stsci.edu/2008/07/caption.html)
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http://heritage.stsci.edu/2008/07/capti ... ion.htmlIf there isn't much cold gas, then where does all the hot gas come from?
X-rays are associated with rather violent phenomena in the universe: accretion disks around pulsars, small parasitic stars which suck matter from larger stars, black holes "dust panning" interstellar space. Generally spoken, these kind of processes, in which cool gas spirals inbound towards a havy object. Due to concentration of flow, the gas is heated up to temperatures which allow for X-ray emission. Such processes usually do not last for long times (compared to the lifetime of a star).
The X-rays seem to come from the outer regions of the galaxy, where the concentration of gas is likely to be less than in the inner regions of the galaxy. Is the galaxy still dustpanning? If the system is the result of a merger between two or more galaxies in a (local) cluster, such a merger is not instantaneous. If several galaxies merge, they will not merge each of them at the same moment. The shape of the remaining galaxy is irregular, like in
http://antwrp.gsfc.nasa.gov/apod/ap061105.html. After enough time the resulting system takes a more common shape. The fact that the system is regularly shaped, is an indication to me that the merger took place at least 100 million years ago. That is quite a long time for an X-ray afterglow.
Apart from the puzzling X-rays, the technique as in overlaying different parts of the EM spectrum and subsequent visualisation in pseudo colors, is amazing, not in the least for reasons of graceful pictures.