Is this the relationship between black holes and dark matter?

According to a study published in the latest issue of The Astrophysical Journal, astrophysicists from the University of Miami, Yale University and the European Space Agency have put forward a view that subverts textbooks: primordial black holes are the source of all dark matter in the universe.

They built an alternative model of how the universe formed and found that all black holes (from those as small as a pinhead to those that span billions of kilometers) were created immediately after the Big Bang and "occupied" all the dark matter.

The study suggests that black holes have existed since the birth of the universe and that these primordial black holes may be the ancestors of the hitherto unexplained dark matter. If the recently launched James Webb Space Telescope can collect conclusive data in the future to prove it, the discovery may change scientific understanding of the origin and nature of two great cosmic mysteries, dark matter and black holes.

"Our study predicts what the early universe would have looked like if dark matter was not an unknown particle but came from black holes formed during the Big Bang - just as Stephen Hawking believed in the 1970s," said Nico Capeluti, assistant professor of physics at the University of Miami.

No more need for “new physics”?

"This will have several important implications," Capeluti said. "First, we will no longer need 'new physics' to explain dark matter. Second, it will help us answer one of the most fascinating questions in modern astrophysics: How could supermassive black holes in the early universe grow so fast?

Given the mechanisms we observe in the modern universe today, they simply wouldn't have had enough time to form. This would also solve a long-standing mystery of why the mass of a galaxy is always proportional to the mass of the supermassive black hole at its center."

Dark matter, which has never been directly observed, is thought to make up the majority of matter in the universe and acts as a scaffold for galaxies to form and grow. On the other hand, black holes, which have been observed and can be found at the centers of most galaxies, have matter so tightly compressed into a single point in space that they exert a strong gravitational pull.

The new research, led by Priyawanda Natarajan, a professor of astronomy and physics at Yale University, and Gint Hasinger, director of science at the European Space Agency, suggests that so-called primordial black holes of various sizes actually "occupy" all the dark matter in the universe.

Black hole, you are all mystery

"The different sizes of black holes remain a mystery," Hasinger explained. "We don't understand how supermassive black holes could have grown so massive in a relatively short period of time since the universe came into existence."

Their model tweaks a theory originally proposed by Hawking and physicist Bernard Carr, who suggested that tiny fluctuations in the density of the universe in the first fractions of a second after the Big Bang could have created an undulating landscape containing "lumpy" regions with extra mass that would collapse into black holes.

The theory has no scientific basis, but Capeluti, Natarajan and Hasinger say it could work with a few modifications. Their model suggests that the first stars and galaxies formed around black holes in the early universe. They also propose that primordial black holes have the ability to grow into supermassive black holes by swallowing nearby gas and stars, or by merging with other black holes.

"Primordial black holes, if they do exist, are likely the seeds from which all supermassive black holes form, including the one at the center of our galaxy," Natarajan said. "This idea is personally very exciting to me because it elegantly unifies two really challenging questions I'm working on - probing the nature of dark matter and the formation and growth of black holes - and solves them both in one fell swoop."

Confirm or deny, or know the answer soon

Primordial black holes may also solve another cosmological puzzle: excess infrared radiation that is synchronized with X-ray emission and detected from distant, dim sources scattered across the universe. Growing primordial black holes would exhibit the "exactly" same radiation signature, the researchers said.

Most importantly, the existence of primordial black holes may be confirmed or denied in the near future - depending on the James Webb Space Telescope, which was launched from French Guiana late last year, and the European Space Agency's Laser Interferometer Space Antenna (LISA) mission planned for the 2030s.

The Webb telescope, developed by NASA, the European Space Agency and the Canadian Space Agency as the successor to the Hubble Space Telescope, can look back more than 13 billion years of cosmic history. If dark matter is made of primordial black holes, then more stars and galaxies would have formed around them in the early universe, and this is what the cosmic time machine will be able to see.

"If the first stars and galaxies were already forming during the so-called 'dark ages', Webb should be able to see evidence for them," Hasinger said.

At the same time, LISA will be able to pick up gravitational wave signals from early mergers of primordial black holes.

Source: Science and Technology Daily

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