A model of supermassive black hole formation based on dark matter halos

The quasar J1243+0100 (Image ALMA (ESO/NAOJ/NRAO), Izumi et al.)
The quasar J1243+0100 (Image ALMA (ESO/NAOJ/NRAO), Izumi et al.)

An article published in “The Astrophysical Journal Letters” reports a model of supermassive black hole formation that explains the rapid growth of the ones observed in the early universe. Wei-Xiang Feng, Hai-Bo Yu, and Yi-Ming Zhong propose a model in which the so-called seeds from which these gigantic black holes are formed are generated by a halo of self-interacting dark matter. According to this model, the collapse that forms the seed is accelerated by baryonic matter, common matter, a unified scenario between the two types of matter.

Observations made in recent decades indicate that it’s normal for a galaxy to have a supermassive black hole at its center whose mass can be millions or even billions of times the Sun’s. Various models have been proposed to explain the formation of black holes of such masses and the most difficult thing is to explain the ones discovered in the early universe. Some supermassive black holes we see as they were when the universe was less than a billion years old were formed in a very short time from an astronomical point of view but how? This new study proposes a solution based on dark matter.

The gravitational effects commonly found in galaxies are far too strong for the amount of matter detectable within them. Dark matter is the most accepted model to explain these effects. According to this model, a halo of dark matter allows common matter to gather in the galaxies that formed the universe as we see it today. According to this new study, there’s much more.

In the new model, the force of gravity attracts the dark matter particles of a halo inward but there’s a thermal pressure that pushes them outward. If the particles heat up when they’re attracted towards the center, their velocity increases, and the pressure also increases until they’re bounced back. If these particles interacted, their heat would transfer to nearby colder ones and would not be bounced back. This mechanism could be behind the formation of a supermassive black hole’s seed.

The halo’s rotation is also important because the self-interactions can generate a viscosity that dissipates the angular momentum. The collapse reduces the size of what is becoming a seed and also its rotation due to viscosity until it becomes a singularity, which is the seed. At that point, its force of gravity starts attracting the common matter nearby.

The amount of dark matter is much higher than common matter, so the process proposed in this new model could occur quickly from an astronomical point of view allowing the generation of supermassive black holes in the early universe. According to the researchers, the self-interacting dark matter model could also explain the motion observed in stars and galaxies.

This model is very interesting, the problem is to test it, like all models concerning dark matter. First of all, attempts are still underway to prove that dark matter really exists and there are alternative models that offer different explanations for the detected gravitational effects. The large amount of energy emitted by quasars, powered by supermassive black holes, allows to detect even the ones in the early universe, so it’s possible to study them. Perhaps, black holes will also help solve the mystery of dark matter.

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