Explanation of the case of missing black holes

May 29. () –

The well understood and highly verified quantum field theorygenerally applied to the study of the very small, has been applied by a group of theoretical physicists to the early universe.

His exploration, accepted in ‘Physical Review Letters’led to the conclusion that there should be many fewer miniature black holes than most models suggest, although observations confirming this should soon be possible.

Although the details are hazy, the general consensus among physicists is that the universe is about 13.8 billion years old, began with an explosion, expanded rapidly in a period called inflation, and at some point went from being homogeneous to containing detail and structure. Most of the universe is empty, but despite this, it appears to be significantly heavier than we can explain by what we can see; We call this discrepancy dark matter, and no one knows what it could be, but evidence is accumulating that they could be black holes, specifically old ones.

“We call them primordial black holes (PBHs), and many researchers feel they are a strong candidate for dark matter, but there would need to be many of them to satisfy that theory,” says Kavli Institute for Physics and Mathematics of the Universe graduate student Jason Kristiano, one of the authors of the study.

“They are interesting for other reasons as well, since since the recent innovation of gravitational wave astronomy, binary black hole mergers have been discovered, which can be explained if PBHs exist in large quantities. But despite these powerful reasons for its expected abundance, we have not seen any directly, and now we have a model that should explain why this is so“.

Kristiano and his supervisor Professor Jun’ichi Yokoyama, currently director of Kavli IPMU and RESCEU, have extensively explored the various models for PBH formation, but found that the main contenders do not align with actual observations of the cosmic microwave background. (CMB), which is a kind of fingerprint left over from the Big Bang explosion that marked the beginning of the universe. And if something does not agree with sound observations, it either cannot be true or, at best, can only reflect part of the picture. In this case, the team used a novel approach to correct the leading model of PBH formation from cosmic inflation so that it better aligns with current observations and can be further verified with upcoming observations from ground-based gravitational wave observatories. of all the world.

“At first, the universe was incredibly small, much smaller than the size of a single atom. Cosmic inflation quickly expanded that by 25 orders of magnitude. At that time, waves traveling through this small space could have had relatively large amplitudes but very short wavelengths What we have discovered is that these small but strong waves can be translated. in an otherwise inexplicable amplification of much longer waves than we see in the current CMB“Yokoyama said.

“We think this is due to occasional cases of coherence between these early short waves, which can be explained using quantum field theory, the strongest theory we have for describing everyday phenomena like photons or electrons. While individual short waves would be relatively powerless, coherent groups would have the power to reshape waves much larger than themselves. This is a rare case in which a theory of something on one extreme scale appears to explain something on the opposite end of the scale.”

If, as Kristiano and Yokoyama suggest, early small-scale fluctuations in the universe affect some of the larger-scale fluctuations we see in the CMB, This could upset the standard explanation of the gross structures of the universe.

“But also, since we can use measurements of wavelengths in the CMB to effectively limit the extent of the corresponding wavelengths in the early universe, this necessarily limits any other phenomena that might depend on these shorter, longer wavelengths. And this is where PBHs come into play again,” he points out.

“It is widely believed that the collapse of short but strong wavelengths in the early universe is what creates primordial black holes,” Kristiano concludes. “Our study suggests that there should be many fewer PBHs than would be needed if they were truly a strong candidate for dark matter events or gravitational waves.”