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The study points to a black black hole produced by a halo collapse of dark matter



How a supermassive black hole originates

Credit: Event Horizon Telescope Collaboration

Supermassive black holes or SMBHs are black holes with masses that are millions to billions times the mass of our sun. The Milky Way hosts an SMBH with mass a few million times the solar mass. Surprisingly, astrophysical observations show that SMBHs already existed when the universe was very young. For example, one billion solar masses exist in black holes when the universe was only 6% of its current age, 1

3.7 billion years. How do these SMBHs in the early universe come from?

A team led by a theoretical physicist at the University of California, Riverside, has come up with an explanation: A massive seed black hole that the collapse of a dark matter halo can produce.

Halo of dark matter is the halo of invisible matter that surrounds a galaxy or cluster of galaxies. Although dark matter has never been detected in laboratories, physicists remain certain that this mysterious substance, which makes up 85% of the universe’s matter, exists. If the visible matter in a galaxy were not embedded in a dark matter halo, this matter would fly apart.

“Physicists are amazed at why SMBHs in the early universe, located in the central regions of dark matter halos, are growing so massively in such a short time,” said Hai-Bo Yu, associate professor of physics and astronomy at UC Riverside, who led the study shown in Astrophysical journal letters. “It’s like a 5-year-old baby weighing 200 pounds, for example. Such a baby would amaze us all because we know the typical weight of a newborn baby and how fast that baby can grow. Where it comes to “black holes, physicists have general expectations for the mass of a black black hole and its growth. The presence of SMBHs suggests that these general expectations have been exceeded, which requires new knowledge. And that’s exciting.”

A black hole is a black hole in its initial phase – akin to the baby stage in a person’s life.

“We can think of two reasons,” Yu added. “The black hole – 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 to produce a massive enough black black hole or achieve a fast enough growth rate? “

“It takes time for black holes to grow massively by accreting surrounding material,” said co-author Yi-Ming Zhong, a postdoctoral researcher at the Kavli Institute for Cosmological Physics at the University of Chicago. “Our paper shows that if dark matter has self-interactions, a halogen’s gravothermal collapse could lead to a massive enough seed black hole. Its growth rate would be more in line with general expectations.”

In astrophysics, a popular mechanism used to explain SMBHs is the collapse of pristine gas in protogalaxes in the early universe.

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

The explanation Yu and his colleagues suggest works as follows:

Particles of dark matter first cluster together under the influence of gravity to form a dark matter halo. During the development of halo, two competing forces act – gravity and pressure -. While gravity pulls dark matter particles inward, the pressure pushes them outward. If dark matter particles have no self-interactions when gravity pulls them toward the central halo, they become hotter, that is, they move faster, the pressure rises efficiently, and they bounce back. In the case of self-interacting dark matter, dark matter self-interactions can transport the heat from the “warmer” particles to the nearby colder ones. This makes it difficult for dark matter particles to bounce back.

Yu explained that the central halo, which would collapse into a black hole, has angular momentum, meaning it rotates. Self-interactions can evoke viscosity or “friction” that disperses the angular momentum. During the collapsing process, the central halo, which has a solid mass, shrinks in radius and is lowered in rotation due to viscosity. As development continues, the central halo eventually collapses into a unique state: a black-black hole. This seed can grow more massively by accreting surrounding baryonic – or visible – substances such as gas and stars.

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

The new work is new, as researchers identify the importance of baryons – common atomic and molecular particles – for this idea to work.

“First, we show the presence of baryons, such as gas and stars, which can significantly accelerate the onset of the gravothermal collapse of a halo, and a black-black hole can form early enough,” Wei-Xiang Feng said. , Yus graduate student and a co-author on paper. “Second, we show that self-interactions can evoke viscosity that disperses the angular momentum left by the central halo. Third, we develop a method to investigate the condition of triggering general relativistic instability of the collapsed halo, ensuring “that a black hole can form if the condition is met.”

Over the past decade, Yu has been exploring new predictions of dark matter self-interactions and their observational consequences. His work has shown that self-interacting dark matter can provide a good explanation for the observed motion of stars and gas in galaxies.

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

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


New research suggests that supermassive black holes can form from dark matter


More information:
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

Provided by the University of California – Riverside



Citation: Study points to a black black hole produced by a halo collapse of dark matter (2021, June 16) retrieved June 16, 2021 from https://phys.org/news/2021-06-seed-black-hole- dark-halo. html

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