Study points to a seed black hole produced by a dark matter halo collapse

Credit: Event Horizon Telescope Collaboration

Supermassive black holes, or SMBHs, are black holes with lots which can be a number of million to billion occasions the mass of our solar. The Milky Way hosts an SMBH with mass a few million occasions the photo voltaic mass. Surprisingly, astrophysical observations present that SMBHs already existed when the universe was very younger. For instance, a billion photo voltaic mass black holes are discovered when the universe was simply 6% of its present age, 13.7 billion years. How do these SMBHs within the early universe originate?

A workforce led by a theoretical physicist on the University of California, Riverside, has provide you with a proof: An enormous seed black hole that the collapse of a dark matter halo may produce.

Dark matter halo is the halo of invisible matter surrounding a galaxy or a cluster of galaxies. Although dark matter has by no means been detected in laboratories, physicists stay assured this mysterious matter that makes up 85% of the universe’s matter exists. Were the seen matter of a galaxy not embedded in a dark matter halo, this matter would fly aside.

“Physicists are puzzled why SMBHs in the early universe, which are located in the central regions of dark matter halos, grow so massively in a short time,” mentioned Hai-Bo Yu, an affiliate professor of physics and astronomy at UC Riverside, who led the research that seems in Astrophysical Journal Letters. “It’s like a 5-year-old child that weighs, say, 200 pounds. Such a child would astonish us all because we know the typical weight of a newborn baby and how fast this baby can grow. Where it comes to black holes, physicists have general expectations about the mass of a seed black hole and its growth rate. The presence of SMBHs suggests these general expectations have been violated, requiring new knowledge. And that’s exciting.”

A seed black hole is a black hole at its preliminary stage—akin to the infant stage within the lifetime of a human.

“We can think of two reasons,” Yu added. “The seed—or ‘baby’—black hole is either much more massive or it grows much faster than we thought, or both. The question that then arises is what are the physical mechanisms for producing a massive enough seed black hole or achieving a fast enough growth rate?”

“It takes time for black holes to grow massive by accreting surrounding matter,” mentioned co-author Yi-Ming Zhong, a postdoctoral researcher on the Kavli Institute for Cosmological Physics on the University of Chicago. “Our paper shows that if dark matter has self-interactions then the gravothermal collapse of a halo can lead to a massive enough seed black hole. Its growth rate would be more consistent with general expectations.”

In astrophysics, a standard mechanism used to clarify SMBHs is the collapse of pristine fuel in protogalaxies within the early universe.

“This mechanism, however, cannot produce a massive enough seed black hole to accommodate newly observed SMBHs—unless the seed black hole experienced an extremely fast growth rate,” Yu mentioned. “Our work provides an alternative explanation: A self-interacting dark matter halo experiences gravothermal instability and its central region collapses into a seed black hole.”

The rationalization Yu and his colleagues suggest works within the following manner:

Dark matter particles first cluster collectively below the affect of gravity and kind a dark matter halo. During the evolution of the halo, two competing forces—gravity and strain—function. While gravity pulls dark matter particles inward, strain pushes them outward. If dark matter particles don’t have any self-interactions, then, as gravity pulls them towards the central halo, they develop into hotter, that’s, they transfer quicker, the strain will increase successfully, and so they bounce again. However, within the case of self-interacting dark matter, dark matter self-interactions can transport the warmth from these “hotter” particles to close by colder ones. This makes it tough for the dark matter particles to bounce again.

Yu defined that the central halo, which might collapse into a black hole, has angular momentum, that means it rotates. The self-interactions can induce viscosity, or “friction,” that dissipates the angular momentum. During the collapse course of, the central halo, which has a fastened mass, shrinks in radius and slows down in rotation due to viscosity. As the evolution continues, the central halo finally collapses into a singular state: a seed black hole. This seed can develop extra large by accreting surrounding baryonic—or seen—matter reminiscent of fuel and stars.

“The advantage of our scenario is that the mass of the seed black hole can be high since it is produced by the collapse of a dark matter halo,” Yu mentioned. “Thus, it can grow into a supermassive black hole in a relatively short timescale.”

The new work is novel in that the researchers establish the significance of baryons—atypical atomic and molecular particles—for this concept to work.

“First, we show the presence of baryons, such as gas and stars, can significantly speed up the onset of the gravothermal collapse of a halo and a seed black hole could be created early enough,” mentioned Wei-Xiang Feng, Yu’s graduate scholar and a co-author on the paper. “Second, we show the self-interactions can induce viscosity that dissipates the angular momentum remnant of the central halo. Third, we develop a method to examine the condition for triggering general relativistic instability of the collapsed halo, which ensures a seed black hole could form if the condition is satisfied.”

Over the previous decade, Yu has explored novel predictions of dark matter self-interactions and their observational penalties. His work has proven that self-interacting dark matter can present a good rationalization for the noticed movement of stars and fuel in galaxies.

“In many galaxies, stars and gas dominate their central regions,” he mentioned. “Thus, it’s natural to ask how the presence of this baryonic matter affects the collapse process. We show it will speed up the onset of the collapse. This feature is exactly what we need to explain the origin of supermassive black holes in the early universe. The self-interactions also lead to viscosity that can dissipate angular momentum of the central halo and further help the collapse process.”

The analysis paper is titled “Seeding Supermassive Black Holes with Self-Interacting Dark Matter: A Unified Scenario with Baryons.”


New research suggests supermassive black holes may kind from dark matter


More info:
Wei-Xiang Feng et al, Seeding Supermassive Black Holes with Self-interacting Dark Matter: A Unified Scenario with Baryons, The Astrophysical Journal Letters (2021). DOI: 10.3847/2041-8213/ac04b0

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University of California – Riverside

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Study points to a seed black hole produced by a dark matter halo collapse (2021, June 16)
retrieved 17 June 2021
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