How supermassive black holes form is still puzzling. But a new study has proposed the idea that dark matter could help create them.
Carlos R. Argüelles, the researcher at Universidad Nacional de La Plata and ICRANet led an investigation about the potential existence of stable galactic cores made of dark matter and surrounded by a diluted dark matter halo.
No one knows exactly how supermassive black holes initially formed. We have observed them existing as early as 800 million years after the Big Bang. But we don’t really know how they could grow so quickly.
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The conventional scenario on how black holes form involves ‘normal’ matter. It involves ordinary baryonic matter collapsing under gravity to form black holes, which then grow over time.
But the international team thinks differently. They suggest supermassive black holes could instead form directly from dark matter in high-density regions in the center of galaxies.
The team believes the centers of these structures could turn out to be concentrated to such an extent that they could likewise collapse into supermassive black holes once a critical threshold is reached.
According to the model, this could have happened much faster than other proposed formation mechanisms. Contrary to current understanding, this could have also allowed ancient supermassive black holes to form before the galaxies they inhabit.
“This new formation scenario may offer a natural explanation for how supermassive black holes formed in the early Universe, without requiring prior star formation or needing to invoke seed black holes with unrealistic accretion rates,” says Dr. Argüelles.
Another possibility of the new model is that the critical mass for collapse into a black hole might not be reached for smaller dark matter halos, for example, those surrounding some dwarf galaxies. This might leave smaller dwarf galaxies with a central dark matter nucleus rather than a black hole.
Such a dark matter core could still mimic the gravitational signatures of a conventional central black hole. Whereas the dark matter outer halo could also explain the observed galaxy rotation curves.
“This model shows how dark matter haloes could harbor dense concentrations at their centers, which may play a crucial role in helping to understand the formation of supermassive black holes,” Dr. Argüelles said.
“Here we’ve proven for the first time that such core-halo dark matter distributions can indeed form in a cosmological framework, and remain stable for the lifetime of the Universe.”
Of course, the researchers believe further studies will shed more light on the formation of the early supermassive black holes. Further investigation could also help us understand whether the centers of non-active galaxies such as the Milky Way may play host to these dense dark matter nuclei.
Scientists published their study in Monthly Notices of the Royal Astronomical Society.