Tag Archives: black hole

Supermassive black holes from dark gulping

I had thought that dark matter should be responsible for only a very small portion of the mass of supermassive black holes in the centers of galaxies, for the same reason that dark matter is distributed much more evenly than ordinary matter. But it turns out I could be very wrong about this.

A young but heavy galaxy
A young but heavy galaxy in the background

Researchers from the University College London modeled the gravitational interactions between dark matter halos and gas embedded in the dark matter. They found out that depending on the thermal properties of dark matter, a small disturbance could cause a rapid gravitational collapse of dark matter into a black hole. Appropriately enough, this rapid collapse of dark matter is called "dark gulping".

Dark matter being what it is, there would hardly be any electromagnetic radiation from the collapse. This would avoid the blasting away of matter by a normal accretion disk which slows down the growth of a black hole, not that dark matter would be affected by radiation in the first place. It would also explain how supermassive black holes could have existed when the universe was less than a billion years old.

If it turns out that dark gulping is indeed responsible for the formation of supermassive black holes, it could provide an interesting look into the properties of dark matter. Because dark gulping is determined by the thermal properties of dark matter, which depends on the degrees of freedom of each dark matter particle, i.e. the number of ways that a dark matter particle could move, rotate, etc., this could give hints to the microscopic interactions of dark matter or even the number of extra dimensions our universe could have.

Discovery of supermassive black hole?

Center of the Milky Way Galaxy
Center of the Milky Way Galaxy

I don't get it. Why do so many news outlets such as the BBC talk as if there had been any uncertainty in the existence of a supermassive black hole in the center of the Milky Way Galaxy? We already had direct evidence of its existence by observing how stars rapidly swing by it in their orbit around the center of the galaxy for years.

While the recent observations and corroboration are exciting in their own right, as it refines previous measurements and make things even more certain, I don't understand the slant a lot of the news media has been putting on the news. Am I missing something?

Quark stars from stellar explosion remnants

When a star with mass similar to our own Sun expends all of its fuel, it settles into becoming a white dwarf. If the star was made up of frictionless, non-quantum mechanical matter, there would be nothing from stopping the star from collapsing into a black hole.

However, all matter are of a quantum mechanical nature, so if matter is packed in tightly enough, degeneracy pressure exerts itself, which is the result of the Pauli exclusion principle, where no two fermionic particles of the same type can occupy the same quantum state. In a white dwarf, electrons are packed so tightly together such that if they get packed any tighter some electrons would end up in the same quantum state, so a pressure that fights against further packing is exerted. This electron degeneracy pressure prevents the star from collapsing into a singularity.

If a star has more than 1.4 times the mass of our Sun, though, then the electron degeneracy pressure is not enough to keep the star from collapsing. Then the particles in the star combine into a homogeneous soup of neutrons, which in turn exert a neutron degeneracy pressure. For stars with up to 2 to 3 times the mass of our Sun, this is enough to prevent gravitational collapse and they exist as neutron stars.

However, neutron degeneracy pressure is not enough for stars with even larger mass. Either the star could collapse into a black hole, or the neutrons could disintegrate into free quarks, and further collapse would be prevented by the quark degeneracy pressure. The thing is that a neutron is probably about 50 to 200 times the mass of its constituent quarks, so a lot of energy should be released when a neutron star collapses into a quark star.

And now Canadian researchers may have identified supernovae explosions which may have resulted in quark stars. These explosions were about 100 times brighter than the typical supernova explosion, and they believe that the release of energy as a neutron disintegrates into its constituent quarks during the formation of quark stars could explain why they are so much brighter. If their hypothesis is confirmed, then we'll need to add one more type of star to the textbooks.