Black holes could form from dark matter, study suggests

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How did supermassive black holes form initially? This is the puzzle that scientists are trying to solve to understand the evolution of galaxies. Rather than conventional training scenarios, a new theoretical study proposes a new mechanism for creating supermassive black holes from dark matter.

Before having a black hole, you normally have to go through the “massive star” box. Standard formation models all involve baryonic matter collapsing on itself to form “gravitational sinks” which then develop over time.

However, we observe the presence of supermassive black holes a few hundred million years after the creation of the Universe. Their formation is still a mystery, as in these times the “seeds” left by the first stars are not believed to be large enough to give birth to such cosmic ogres. The big question is: how did they come about?

Some researchers have already proposed the idea that sufficiently massive clouds of gas and dust can end up collapsing directly on themselves, ultimately giving rise to black holes without going through the “stars” box.

As part of new theoretical work, astronomers are offering another alternative. According to them, some primitive supermassive black holes could form directly from dark matter in high density regions of galactic centers.

What is dark matter?

Dark matter is one of the greatest mysteries in modern astrophysics. We know that it exists through the gravitational influence it exerts on its environment, but we do not yet know its composition. As this matter is unfortunately insensitive to electromagnetic force, it cannot absorb, reflect or emit light. That is why it is invisible to us.

And there are many ! The baryonic matter, known as “ordinary” (that which composes your body like that of the stars and the planets) represents in fact less than 5% of all matter in the Universe, against about 26.8% dark matter (the rest is dark energy).

That being said, this new research suggests the potential existence of stable galactic nuclei made of dark matter and surrounded by a halo of diluted dark matter, finding that the cores of these structures could become so concentrated that they could also collapse. into supermassive black holes from a critical threshold.

Illustration of a spiral galaxy embedded in a greater distribution of invisible dark matter (halo colored in blue). Credits: ESO / L. Calçada

According to the model, forming black holes in this way could occur much faster than by other proposed formation mechanisms, and therefore allow these supermassive ogres to form in the early Universe without requiring prior star formation.

These works are published in the Monthly notices from the Royal Astronomical Society.

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