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Q&A: Galaxies, Galaxy Clusters, AGN, and Quasars
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Q:
I read an article about the discovery of merging galaxies. In this
article is said that this is happening 10 billion light years away.
Does this mean that the events you saw actually happened 10 billion
years ago? So at this point shouldn't the galaxies already be merged
and maybe transformed into a quasar?
A:
Perhaps you've seen images from the
Chandra website of such distant objects. For example, the cluster of
galaxies called 3C294 is about 10 billion light years away:
http://chandra.harvard.edu/press/01_releases/press_021501.html
You are correct in your assumption. If an object is 10 billion light
years away, and we receive light from it, whatever event caused the
light to be emitted happened 10 billion years ago. So indeed, the
galaxy merger we view today from Earth has already merged and evolved
for 10 billion more years, and probably bears little resemblance to the
current image. More information
As to it turning into a quasar, that is actually an open question. It
may be that if each galaxy contains a supermassive black hole in the
center, then the merging of these black holes could power a quasar (http://chandra.harvard.edu/xray_sources/quasars.html), or more likely
a gamma ray burst (http://chandra.harvard.edu/xray_sources/grb.html).
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