Could quasars produce elements heavier than oxygen?

Question

I have read that supernovae are the main producers of elements heavier than oxygen. I just wonder whether quasars, which have been around a long time just like supernovae have, could have had a comparable material effect on the universe. With all the energy they produce, you'd think they would somehow affect material composition. If not heavy elements, maybe they are the creators of dark matter?

Answer 1

The reason supernovae enrich the interstellar medium with heavy elements is that they synthesise those elements in the core of the star where the temperature and pressure are extreme, then explode and scatter those elements into the surrounding space. So the supernovae do two things:

1. achieve enormous temperatures and pressures

2. explode

By contrast quasars are competely different. Quasars are (probably) supermassive black holes and the radiation they produce is from matter heated as it falls toward the event horizon. This matter forms an accretion disk around the quasar but the density and temperature are far lower than in a massive star. I'm not sure if nucleosynthesis occurs at all in an accretion disk, but if it does only the lighter nuclei like helium are likely to be formed.

So the accretion disk cannot be a source of heavy elements. What goes on inside the black hole itself is another matter, but then unlike supernovae black holes don't explode so anything that falls into them never gets out. The end result is that quasars are not a source of elements heavier than oxygen.

Answer 2

John Rennie's answer covers a lot of points that I won't repeat, but as was pointed out in the comments it doesn't mention the black hole jets. This is a little ways off my expertise, but my understanding is that the jets are a source of relativistic particles, i.e. cosmic rays (though not the only source, I think). Cosmic rays hitting other material, or colliding with each other, can trigger fission and fusion reactions via a process called cosmic ray spallation. This produces mostly light elements, but apparently small amounts of stuff as heavy as $^{127}_{~~53}{\rm I}$ (!) can be produced.