...The setup starts with an idea from last year. Certain exotic forms of dark matter, arranged in a halo with a particular relationship between pressure and density, can produce black holes with no singularity at the center. These are so-called "regular black holes," where the equations stay sensible all the way to the center. Tan and Wang asked what happens if you drop an ordinary neutron star into the middle of one of these halos...

...The crucial point in this model is that nothing collapsed. The gravity making the horizon comes from the star and the halo combined, with the dark matter contributing roughly as much mass as the star itself...

...The dark matter densities this requires are far greater than anything astronomers actually expect dark matter to reach. This is not a claim about objects out there in the sky, but more of a thought experiment with the mathematics filled in. It says the inside of a black hole need not be the end of physics. There is at least one solution in which it's a place, with something in it...