The early universe contained far fewer miniatures Black holes than previously thought, making the origin of the missing matter in our universe an even greater mystery, new research has shown.
Miniature or primordial black holes (PBHs) are black holes thought to have formed in the first fractions of a second after the Big Bang. According to leading theories, these dime-sized singularities emerged from regions of dense, hot gas that were rapidly collapsing.
Pockets of infinitely dense spacetime are how many physicists explain the universe’s dark matter, a mysterious entity that, despite being completely invisible, makes the universe much more complex than can be explained by the matter we see.
But while the hypothesis is popular, it has one big problem: we have yet to directly observe primordial black holes. Now a new study has offered a possible explanation for why they didn’t form, opening up the cosmological problem of dark matter to wider speculation.
According to the research, the modern universe could have formed with far fewer primordial black holes than previous models estimated. The researchers published their findings on May 29 in the journal Physical Review Letters.
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“Many researchers believe that [primordial black holes] are strong candidates for dark matter, but there would have to be a lot of them to satisfy that theory,” lead author Jason Christianograduate student in theoretical physics at the University of Tokyo, it is stated in the press release. “They are also interesting for other reasons, since the recent innovation of gravitational wave astronomy has led to the discovery of merging binary black holes, which can be explained if PBHs exist in large numbers. But despite these strong reasons for their expected abundance, we have seen nothing directly, and now we have a model that should explain why this is the case.”
Hole in the picture
The universe began 13.8 billion years ago with Big bangcausing the young cosmos to explode outwards due to an invisible force known as dark energy.
As the universe grew, ordinary matter, interacting with light, condensed around clumps of invisible dark matter to create the first galaxies, connected by a vast cosmic network. Today, cosmologists think that ordinary matter, dark matter and dark energy make up about 5%, 25% and 70% of the composition of the universe, respectively.
In the beginning, the universe was opaque, a plasma soup through which light could not pass without being trapped by electromagnetic fields produced by moving charges. Yet after 380,000 years of cooling and expansion, the plasma finally recombined into neutral matter, emitting microwave static that became the universe’s first light, the cosmic microwave background (CMB).
Cosmologists searched for these early black holes by studying this first child’s picture of the universe. However, none have been found so far.
Some physicists think that there is a possibility that they have not discovered the huge number of primordial black holes needed to explain dark matter simply because they have yet to learn how to detect them.
But by applying a model built on an advanced form of quantum mechanics called quantum field theory to the problem, the researchers behind the new study reached a different conclusion — we can’t find any primordial black holes because most of them simply aren’t there.
It is believed that primordial black holes were created by the collapse of short but powerful gravitational waves that rippled through the universe. By applying their model to these waves, the researchers found that it may take far fewer of these waves to combine than other theories estimate to form larger structures throughout the universe. And the fewer waves needed to recreate the image, the fewer the original black holes.
“It is widely believed that the collapse of short but strong wavelengths in the early universe is what creates primordial black holes,” Kristiano said. “Our study suggests that there should be far fewer PBHs than would be necessary if they are indeed strong candidates for dark matter or gravitational wave events.”
To confirm their theory, the researchers will look to future, hypersensitive gravitational wave detectors like The Laser Interferometer Space Antenna (LISA) project.which should be sent into space on the Ariane 3 rocket in 2035.
