Dark Matter puzzle?

Astronomers Find Black Holes Do Not Absorb Dark Matter

The media produced breathless copy like the above, which comes from one of the more considered and sensible space science news-sites, Universe Today. The ‘headline’ was inspired by this paper…

An upper limit to the central density of dark matter haloes from consistency with the presence of massive central black holes

…which does seriously challenge the naive model of dark matter in its “plain Dark Matter” form – i.e. responds to gravity and only interacts with other Dark Matter via annihilation reactions. But what if Dark Matter is more complicated? Some theories argue for other Dark Matter forces that it alone feels. If Dark Matter is “Shadow Matter”, which has a full suite of Standard Model forces, but in mirror reflection to Normal Matter, then Dark Matter is subject to “dark light”, its own kind of electromagnetic forces. Remember all varieties of proposed Dark Matter feel gravity and a central galactic black-hole is going to be a black hole in either the Normal Matter or Shadow Matter ‘universes’. But there’s more Shadow Matter than Normal Matter and, due to differences in Big Bang Nucleosynthesis, the ratio of hydrogen’ to helium’ is lower than the Normal Matter H/He ratio. The Shadow Universe began old, with a higher metallicity driven opacity in its star-forming gases. That means in the Shadow Universe the Galaxies never condensed into flat disks because supernova blew them into huge hot bubbles, surrounding Normal Matter galaxies as the observed Dark Matter haloes to the present day. Thus Shadow Quasars, and their black hole engines, blew away any excess central density in the Shadow galaxies and the central black holes were starved of Dark Matter, as the new study observes.

Thus the new study isn’t telling us that Dark Matter is somehow immune to Black Holes, which is utterly contrary to the gravitational justification for Dark Matter in the first place. Instead Dark Matter is more complex than the simple variety invoked as the minimal working hypothesis. There’s much more to learn about the Shadow Universe than we first thought – surely that’s got to be a good thing?

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