Researchers at the University of Tokyo’s Research Center for the Early Universe (RESCEU) and Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI) have applied well-known and highly verified quantum field theory, which is typically used to study the very small, to a new target: the early universe. Their investigation led them to the conclusion that there should be significantly fewer small black holes than most theories predict, however measurements to validate this should be available soon. The precise type of black hole in question may be a candidate for dark matter.
The details are hazy, scientists generally agree that the universe is around 13.8 billion years old, began with a bang, expanded rapidly during a period known as inflation, and at some point went from being homogeneous to holding complexity and structure. The majority of the universe is empty, but it looks to be substantially heavier than can be explained by what we can see; this difference is known as dark matter, and no one knows what it is, although evidence suggests that it is black holes, particularly old ones.
Black Hole
“We call them primordial black holes (PBH), and many researchers feel they are a strong candidate for dark matter, but there would need to be plenty of them to satisfy that theory,” Jason Kristiano, a graduate student, said. “They are also important for other reasons, as since the recent development of gravitational wave astronomy, there have been findings of binary black hole mergers, which can be explained if PBHs exist in huge numbers. Despite these compelling arguments for their projected abundance, we have yet to observe any, and now we have a model that should explain why.”
Kristiano and his supervisor, Professor Jun’ichi Yokoyama, who is now the director of Kavli IPMU and RESCEU, thoroughly investigated the various models for PBH formation but discovered that the leading contenders do not correspond to actual observations of the cosmic microwave background (CMB), which is similar to a leftover fingerprint from the Big Bang explosion that marked the beginning of the universe. And if something contradicts solid observations, it is either false or simply provides a partial picture. In this example, the scientists employed a novel strategy to update the leading model of PBH creation from cosmic inflation such that it better correlates with current results and could be further verified with future observations by terrestrial gravitational wave detectors around the world.
The universe’s initial size was small, but cosmic inflation expanded it by 25 orders of magnitude, allowing waves with large amplitudes but short wavelengths to amplify longer ones in the present Central Binary. This is due to occasional coherence between early short waves, which can be explained using quantum field theory. If these small-scale fluctuations affect larger-scale fluctuations in the Central Binary, it might alter the standard explanation of coarse structures in the universe.
“It is widely believed that the collapse of short but strong wavelengths in the early universe is what creates primordial black holes,” stated Kristiano. “Our study suggests there should be far fewer PBHs than would be needed if they are indeed a strong candidate for dark matter or gravitational wave events.”
Reference – The case of the missing black holes