Japanese scientists have put together a new model to explain some of the universe’s biggest mysteries: missing black holes and the possible existence of dark matter.
The results of this study have been published in a peer-reviewed academic journal Physical examination letters.
If true, the results of this research will help paint a deeper picture of the early universe and the structure of the cosmos itself.
Cosmic Conundrums: Black Holes, Dark Matter, and the Birth of the Universe
This research deals with some very complex and still not fully understood concepts in astrophysics, so let’s break it down one by one.
First, let’s start with the simplest: the universe itself.
The universe is believed to be about 13.8 billion years old. Although it started incredibly small, it has since spread into the almost infinite expanses of space that we all know today. After the Big Bang, the universe went from this tiny singularity to a paradoxically vibrant but empty space populated by stars, galaxies, and other structures, while also having a vast amount of emptiness.
But the cosmic microwave background (CMB) is also present in the universe. These are essentially the remnants of the Big Bang itself and can be found everywhere.
Now let’s talk about dark matter.
Simply put, we don’t know what dark matter is. We think of dark matter as the invisible matter that exists throughout the universe, making the collective mass of everything in the universe much heavier than it appears.
In theory, dark matter is an invisible substance that does not emit light and makes up over 85% of the matter in the observable universe. The Standard Model of cosmology also states that it is vital to the continued evolution of the universe.
We only know that it exists—presumably, since some researchers still debate its existence—because of gravity. Gravity as we know it is explained by Albert Einstein’s Theory of General Relativity. Anything that cannot be explained by it is generally thought to be due to the influence of dark matter.
However, some researchers have proposed a different possible explanation for dark matter, and that’s our next topic: black holes.
Black holes are massive concentrations of gravity so strong that nothing, not even light, can escape, making them invisible. Like dark matter, the only way scientists could tell they existed was through gravity, and like dark matter, they play a key role in how the universe works.
However, unlike dark matter, which is so mysterious that some scientists doubt it even exists, black holes are a very well-established scientific fact. Most of them form when a large star dies, which plays a major role in the life cycles of stars and galaxies.
But research also suggests that black holes may not only form when stars die. Rather, they may have existed since the beginning of the universe.
These hypothetical black holes from the dawn of the universe are known as primordial black holes (PBHs) and would predate the birth of stars.
But in addition to solving many other mysteries, such as the James Webb Space Telescope’s discoveries of massive galaxies in the early universe that shouldn’t have been able to form at that time, scientists also think they can solve another mystery: dark matter.
Black holes are incredibly dense and heavy, so in theory they could help explain the extra mass in the universe attributed to dark matter. In addition, they could help explain other mysteries. But all this depends on one thing: there must be enough of them in the universe. So far, scientists have not been able to find them.
“Following the recent innovation in gravitational wave astronomy, there have been discoveries of merging binary black holes, which can be explained if PBHs exist in large quantities,” said graduate student Jason Christiano. “But despite these strong reasons for their expected abundance, we haven’t seen any directly, and now we have a model that should explain why this is so.”
The study of the formation of primordial black holes has problems with the researchers behind the study. For example, the CMB does not seem to support the leading proponents of how these black holes would form.
So, when faced with a model that seemed at odds with the established CMB data, the researchers did the only thing they could: they adjusted the model to ensure it matched the data.
“In the beginning, the universe was incredibly small, much smaller than the size of an atom. Cosmic inflation rapidly expanded by 25 orders of magnitude. At that time, waves traveling through this small space could have relatively large amplitudes but very short wavelengths waves. What we found is that these small but strong waves can become an inexplicable amplification of the much longer waves we see in the current CMB,” said Prof. Junichi Yokoyama, director of the Early Universe Research Center (RESCEU) and the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI) at the University of Tokyo.
“We believe this is due to random instances of coherence between these early short waves, which can be explained using quantum field theory, the most stable theory we have to describe everyday phenomena like photons or electrons. While individual short waves would be relatively powerless, coherent groups would have the power to alter waves much larger than themselves. This is a rare case where a theory of something at one extreme seems to explain something at the opposite end of the scale.”
So we are dealing with wavelengths and fluctuations. The idea is quite complicated, but simply put, small-scale fluctuations in the early universe actually affect larger fluctuations in the CMB. It’s a big deal, but it matters because it has new implications for anything that relies on these kinds of wavelengths.
And it is these short but powerful wavelengths that are thought to create primordial black holes.
In general, primordial black holes should still exist. But based on this new model, there shouldn’t be as many of them as previously thought.
But all this is still theoretical. What is needed is actual research to back it up. Fortunately, a joint observing mission between the US, Italy and Japan is doing just that: studying what are likely primordial black holes.
The results of this study will determine how accurate this model is.
