Astrophysicists Ask a Simple Question -- What if Dark Matter is Just Black Holes?
Proposing an alternative model for how the universe came to be, a team of astrophysicists suggests that all black holes—from those as tiny as a pin head to those covering billions of miles—were created instantly after the Big Bang and account for all dark matter. That’s the implication of a study by astrophysicists at the University of Miami, Yale University, and the European Space Agency that suggests that black holes have existed since the beginning of the universe and that these primordial black holes could be as-of-yet unexplained dark matter. Dark matter — which has never been directly observed — is thought to constitute the majority of matter in the universe and act as the unseen scaffolding upon which galaxies form and develop. Physicists have spent years looking at a variety of dark matter candidates, including hypothetical particles such as sterile neutrinos, Weakly Interacting Massive Particles (WIMPS), and axions. If this new black hole hypothesis is proven true with data collected from the James Webb Space Telescope, the discovery may transform scientific understanding of the origins and nature of two cosmic mysteries: dark matter and black holes. (Image Credit: Yale University, University of Miami, and the European Space Agency - ESA)
Astrophysicists Ask a Simple Question -- What if Dark Matter is Just Black Holes?
How did supermassive black holes form? What is dark matter? In an alternative model for how the Universe came to be, as compared to the ‘textbook’ history of the Universe, a team of astronomers propose that both of these cosmic mysteries could be explained by so-called ‘primordial black holes.’
Nico Cappelluti (University of Miami), Günther Hasinger (ESA Science Director) and Priyamvada Natarajan (Yale University), suggest that black holes existed since the beginning of the Universe and that these primordial black holes could be the as-of-yet unexplained dark matter.
“Black holes of different sizes are still a mystery. We don’t understand how supermassive black holes could have grown so huge in the relatively short time available since the Universe existed,” explains Günther Hasinger.
At the other end of the scale, there might also be very small black holes, as suggested by observations from ESA’s Gaia, for example. If they exist, they are too small to have formed from dying stars.
“Our study shows that without introducing new particles or new physics, we can solve mysteries of modern cosmology from the nature of dark matter itself to the origin of super-massive black holes," says Nico Cappelluti, an assistant professor of physics at the University of Miami.
“Our study predicts how the early universe would look if, instead of unknown particles, dark matter was made by black holes formed during the Big Bang—as Stephen Hawking suggested in the 1970s,” said Nico Cappelluti.
“This would have several important implications,” continued Cappelluti. “First, we would not need ‘new physics’ to explain dark matter. Moreover, this would help us to answer one of the most compelling questions of modern astrophysics: How could supermassive black holes in the early Universe have grown so big so fast? Given the mechanisms we observe today in the modern universe, they would not have had enough time to form. This would also solve the long-standing mystery of why the mass of a galaxy is always proportional to the mass of the super massive black hole in its center.”
If most of the black holes formed immediately after the Big Bang, they could have started merging in the early Universe, forming more and more massive black holes over time. ESA’s future gravitational wave space observatory, LISA, might pick up the signals of those mergers if primordial black holes exist. Small black holes might simply be the primordial black holes that have not merged into larger ones yet.
According to this model, the Universe would be filled with black holes all over. Stars would start to form around these clumps of ‘dark matter,’ creating solar systems and galaxies over billions of years. If the first stars indeed formed around primordial black holes, they would exist earlier in the Universe than is expected by the ‘standard’ model.
“Primordial black holes, if they do exist, could well be the seeds from which all the supermassive black holes form, including the one at the center of the Milky Way,” Natarajan said. “What I find personally super exciting about this idea is how it elegantly unifies the two really challenging problems that I work on—that of probing the nature of dark matter and the formation and growth of black holes—and resolves them in one fell swoop.”
Dark matter — which has never been directly observed — is thought to constitute the majority of matter in the universe and act as the unseen scaffolding upon which galaxies form and develop. Physicists have spent years testing a variety of dark matter candidates, including hypothetical particles such as sterile neutrinos, Weakly Interacting Massive Particles (WIMPS), and axions.
Although the theory has not yet gained traction within the wider scientific community — this new black hole study suggests that, if modified slightly, it could have explanatory power after all.
If most of the primordial black holes were “born” at a size roughly 1.4 times the mass of Earth’s sun, they could potentially account for all dark matter, said Yale professor of astronomy and physics Priyamvada Natarajan.
Natarajan and her colleagues say their new model shows that the first stars and galaxies would have formed around black holes in the early universe. Also, she said, primordial black holes would have had the ability to grow into supermassive black holes by feasting on gas and stars in their vicinity, or by merging with other black holes.
ESA’s Euclid mission, which will probe the dark Universe in greater detail than ever before, could play a role in the quest to identify primordial black holes as dark matter candidates.
The NASA/ESA/CSA James Webb Space Telescope, will further shed light on this mystery.
“If the first stars and galaxies already formed in the so-called ‘dark ages,’ Webb should be able to see evidence of them,” adds Günther.
For more information:
https://news.yale.edu/2021/12/16/black-holes-and-dark-matter-are-they-one-and-same
https://news.miami.edu/stories/2021/12/are-black-holes-and-dark-matter-the-same.html
https://astromart.com/news/show/does-modified-newtonian-dynamics-negate-the-need-for-dark-matter
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