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Why are there no quasars younger than 13 billion years old? I have researched the emission spectrum of quasars and found only hydrogen. Could it be that after a billion years after the Big Bang, heavier elements transformed quasars into Black Holes?

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Where do you get the idea that there are no quasars younger than 13 billion years old and what do you mean by the "age" of a quasar? Also the quasar phenomenon is thought to be due to the accretion of matter into supermassive black holes.

Many quasars are seen at very high redshifts of 8 or so, and therefore can be no older than a billion years. There may be a problem eventually in finding younger quasars because there must be a certain amount of time required for the supermassive black holes at their centres to grow.

There appears to be a peak in the co-moving population density of quasars at redshifts of between 2 to 2.5. Depending on exactly which cosmological parameters one adopts, these quasars are about 5 billion years old (where age here refers to time since the big-bang).

The nearest quasars to us are about 1 billion light years away (e.g. 3C 273, Mkn 231), but quasars appear to be getting rarer at lower redshifts, indicating that quasars are gradually "turning off".

Thus I don't know what to make of your question - quasars are apparent over a very broad range of cosmic epochs, from about 1 billion years after the big bang to about 1 billion years in the past.

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  • $\begingroup$ The nearest quasar is actually just 600 million light-years away (Mrk 231): nasa.gov/feature/goddard/… $\endgroup$
    – mpv
    Commented Oct 20, 2015 at 9:44
  • $\begingroup$ @mpv Indeed - edited. Though I'm not sure what the definition is. $\endgroup$
    – ProfRob
    Commented Oct 20, 2015 at 11:30
  • $\begingroup$ Not to critique this great answer (really, I do like it), but I think by "new quasars" the OP didn't mean that they look young when we see them but ones that appear to have formed within, say, the last billion years. A quasar with a redshift of 8 may be a billion years or less old when it emitted the light we are observing, but if it's still around now, it's an old fuddy duddy quasar. $\endgroup$
    – Jim
    Commented Oct 20, 2015 at 12:17
  • $\begingroup$ @Jim I agree about the lack of clarity. I have another answer that I placed today that explains why recent qusar activity is rare. $\endgroup$
    – ProfRob
    Commented Oct 20, 2015 at 14:19
  • $\begingroup$ @Jim actually if you look a the OP carefully, the hypothesis is made that all the quasar action happened within 1 billion years of the big bang. So I don't think I have misinterpreted. $\endgroup$
    – ProfRob
    Commented Oct 20, 2015 at 14:22

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