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Turbulent disk of gas revolving around a black hole. Credit: NASA Goddard Space Flight Center / Jeremy Schnittman
A new theoretical study has proposed a new mechanism for creating supermassive black holes from dark matter. The international team found that rather than conventional formation scenarios involving “normal” matter, supermassive black holes could instead form directly from dark matter in high-density regions at the center of galaxies. The result has key implications for cosmology in the early Universe, and is published in Monthly notices from the Royal Astronomical Society.
One of the biggest issues in studying the evolution of galaxies today is exactly how supermassive black holes initially formed. Supermassive black holes have been observed as early as 800 million years after the big Bang, and how they could grow so quickly remains unexplained.
Standard formation patterns involve normal baryonic matter – the atoms and elements that make up stars, planets, and all visible objects – collapsing under gravity to form black holes, which then expand over time. However, the new work investigates the potential existence of stable galactic nuclei made of dark matter and surrounded by a halo of dilute dark matter, finding that the centers of these structures could become so concentrated that they could also collapse into holes. supermassive black when critical. threshold is reached.
Artist’s impression of a spiral galaxy embedded in a larger distribution of invisible dark matter, known as the dark matter halo (colored blue). Studies examining the formation of dark matter halos have suggested that each halo could harbor a very dense core of dark matter, which could potentially mimic the effects of a central black hole, or possibly collapse to form one. Credit: ESO / L. Calçada
According to the model, this could have happened much faster than other proposed formation mechanisms, and would have allowed supermassive black holes in the early Universe to form before the galaxies they inhabit, contrary to current understanding. .
Carlos R. Argüelles, the researcher at Universidad Nacional de La Plata and ICRANet who led the investigation comments: “This new formation scenario may offer a natural explanation for how supermassive black holes formed at the start of the Universe, without requiring prior star formation or the need to summon seed black holes with unrealistic accretion rates. “
Another intriguing consequence of the new model is that the critical mass for collapse in one black hole may not be achieved for smaller dark matter halos, for example those surrounding some dwarf galaxies. The authors suggest that this could then leave smaller dwarf galaxies with a central core of dark matter rather than the expected black hole. Such a dark matter core could still mimic the gravitational signatures of a conventional central black hole, while the outer dark matter halo could also explain the observed galaxy rotation curves.
“This model shows how dark matter halos can harbor dense concentrations at their center, which can play a crucial role in helping to understand the formation of supermassive black holes,” added Carlos.
“Here we have proven for the first time that such nucleus-halo dark matter distributions can indeed form in a cosmological setting and remain stable throughout the lifetime of the Universe.”
The authors hope that further studies will better understand the formation of supermassive black holes in the very early days of our Universe, as well as determine whether the centers of non-active galaxies, including our own Milky Way, can accommodate these dense dark matter nuclei.
Reference: “On the formation and stability of fermionic dark matter halos in a cosmological framework” by Carlos R Argüelles, Manuel I Díaz, Andreas Krut and Rafael Yunis, December 31, 2020, Monthly notices from the Royal Astronomical Society.
DOI: 10.1093 / mnras / staa3986
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