When a star made from protons neutrons and electrons becomes a black hole that black hole can emit protons neutrons and electrons as Hawking radiation. Dark matter is unusual matter: is there any evidence for unusual particles being radiated by black holes ( that may have swallowed dark matter) ? If not perhaps black holes can't be made from dark matter because it doesn't have a particle antiparticle pairing that would enable the emission of hawking radiation.
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$\begingroup$ note that having a distinct anti particle is not a requirement. Photons are part (perhaps a dominant part) of Hawking radiation (in theory) and the photon is its own anti-particle. However there is no evidence of radiation of any kind being emitted. Hawking radiation remains a theoretical thing. $\endgroup$– James KCommented May 21, 2023 at 4:30
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$\begingroup$ Dark matter must be able to fall into black holes or else it is repelled by them and it is not because then stars would repel it too being made from the same material as black holes $\endgroup$– user50918Commented May 21, 2023 at 8:59
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$\begingroup$ The matter that falls into a black hole is irrelevant. This is part of the "no hair" theorem. A black hole made of normal matter, a black hole made of dark matter, a black hole made entirely of light, or a black hole made of a mixture: all would have exactly the same properties of mass, charge, rotation, and nothing else. $\endgroup$– James KCommented May 21, 2023 at 9:52
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Black holes are expected to be able to radiate every particle. There is no connection to what kinds of particles fell into the black hole.
And indeed, evaporating black holes in the early universe have been considered as a production mechanism for dark matter (example).
The caveat is that a particle is only efficiently produced if its mass is lower than the black hole's temperature. Stellar remnant black holes today have Hawking temperatures around $10^{-12}$ eV. Most dark matter candidates are not that light, although some are.
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$\begingroup$ The lower limit for dark matter mass in the link for light DM gives a de Broglie wavelength of about one sun earth distance 10^11 metres. $\endgroup$– user50918Commented May 21, 2023 at 9:23