I just had a conceptual question, hopefully it makes for some really interesting answers.

I was wondering, as most galaxies have an SMBH at their centre (see Kormandy & Richstone 1995; Richstone et al. 1998), could dark matter accrete onto the SMBH over time (perhaps perturbed by a galaxy collision, interaction or merger) and then recycle this matter as energy? Can dark matter help an SMBH grow?

  • $\begingroup$ Could you clarify what you mean by "recycle this matter as energy" ? $\endgroup$
    – James K
    Nov 27, 2015 at 23:36

1 Answer 1


The accretion of dark matter by a black hole is possible, but difficult. Unless its trajectory takes it into the black hole, then it will simply approach the black hole, speed up and then escape again, since non-interacting dark matter cannot dissipate energy in any way.

Presuming a black hole did accrete the dark matter then the energy possessed by the dark matter would become part of the rest mass energy of the black hole. So yes, the black hole would grow. Not sure what you mean by recycle the energy. Energy is always recycled (conserved). If you mean can the black hole lose its rest mass energy? I suppose it may do via Hawking radiation, but this is vanishingly small for a SMBH. The dark matter will also carry angular momentum into the BH and there are ways that this rotational energy can be extracted (e.g. the Penrose process https://en.m.wikipedia.org/wiki/Penrose_process ).


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