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During its lifetime, a star can synthesize elements to iron because of the pressure and temperature. A neutron star is composed of iron nuclei 56 and up to krypton 118.

According to that, a black hole (which concentrates matter to an increasingly tiny space during infall) must also have an unimaginable pressure/temperature during its formation and as additional matter falls into it.

Can it therefore synthesize new elements?

uhoh
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Astrea
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    Why do you say a neutron star has iron and krypton? A neutron star is composed of mostly neutrons and a small amount of electrons and protons. At high temperatures there are too many high-energy gamma rays that photodisintegrate nuclei. – eshaya Jul 19 '19 at 20:09
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    Please see https://physics.stackexchange.com/a/141876/123208 We don't have a quantum gravity theory, so we can't really talk about the ultimate fate of matter in a BH. But it's likely that atoms falling into a BH get ripped apart, and protons & neutrons probably can't survive either. – PM 2Ring Jul 19 '19 at 20:12
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    @eshaya A neutron star has a crust of relatively normal nuclei, albeit rather distorted from the gravity, and those nuclei have higher neutron : proton ratios than normal. Please see https://astronomy.stackexchange.com/a/23173/16685 for further details. – PM 2Ring Jul 19 '19 at 20:19
  • @Astrea I've modified your question a bit so that it can be answerable. "Is a black hole made of heavy elements" can't really be answered easily, but the fate of matter during it's formation process, and as more matter falls in later might be answerable. – uhoh Jul 19 '19 at 21:06
  • @PM2Ring I've made an edit/adjustment, hopefully this is more answerable. – uhoh Jul 19 '19 at 21:06
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    @uhoh I still have nothing to say, apart from "Probably not". And it looks like Rob J doesn't want to answer it either. I guess you might get some exotic nuclei during the initial collapse, but nothing beyond what happens in a neutron star. And afterwards, infalling matter is too busy being spaghettified to do anything constructive. ;) – PM 2Ring Jul 19 '19 at 22:52
  • It's probably not consequential, but somehow now I find this really intriguing and metaphoric; does infalling matter have one last chance to do something even if nobody outside the event horizon will ever know? "look at me, I nucleosynthesize, therefore I am!" – uhoh Jul 19 '19 at 23:11
  • We cannot say what's inside a black hole because nothing escapes it. Around black holes, the energy of infalling material is high, but I doubt it is high enough to synthesize something new. However, it is known that in its creation process, a supernova, new elements are created. – jan.sende Jul 20 '19 at 23:33
  • Ok, thank you all for your comments and modifications. So we are searching for a quantum gravity theory to be able to better understand what happens in a BH. – Astrea Jul 22 '19 at 12:50
  • It would be nice to unify physics so that everything can be modeled by a single theory. Currently, we have GR which describes gravity, but which is oblivious to quantum effects, and QM which describes everything else, but which is ignorant of gravity. – PM 2Ring Jul 25 '19 at 15:13
  • However, there aren't many situations that need both GR & QM. The most important is the very earliest moments of the Big Bang (less than a nanosecond); Quantum Gravity should also tell us about the ultimate fundamental nature of spacetime. It will tell us if Hawking radiation is real or not. It will also tell us exactly what goes on at the core of a black hole, but because of the event horizon we will never be able to make observations that allow us to verify those predictions. – PM 2Ring Jul 25 '19 at 15:15
  • I still think we can answer the question with a "No". We do know that at high pressures and densities, as are already reached in neutron star cores and are much higher than in atomic nuclei, no protons and certainly no regular atoms can exist. I cant see how the further collapse to a BH or quantum-gravity could change that. The only thing that can happen is the r-process outside of the core during the supernova. – SpaceCore Jul 25 '19 at 16:03
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    @uhoh thank you for boosting this question with bounties ! – Astrea Jul 26 '19 at 13:59

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After a google search the answer is yes, in theory. There is nucleosynthesis associated with the Black Hole accretion disks, see here, here and here. These sources look at the nucleosynthesis in the hotter parts of the accretion disks surrounding black holes, and how this is effected by the neutrinos produced.

It is also proposed that its possible for very small mass (10e-9 Mass of sun) black holes to be devoured by a neutron star (see here) and produce many of the heavier elements. This method starts with primordial black holes which can be of the required mass compacted into a region the size of a single atom. This tiny black hole could crash into a neutron star and initiate the r-process for nucleosynthesis.

Natsfan
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