What if the dark matter we're so desperately searching for is actually made up of primordial black holes?
Is there a connection between dark matter and primordial black holes? What if the mysterious dark matter that scientists struggle to discover is actually made from black holes that existed in the early universe?
The history of dark matter began in 1933 when astronomer Fritz Zwicky studied the velocity distribution of galaxies in the cluster located in the constellation Coma Berenices. He found that the galaxies in the cluster are moving too fast, and if only the visible matter is taken into account, the cluster could not be stable – the galaxies would simply be scattered in different directions. Zwicky suggested that they were held together by an invisible gravitational substance – Dark Matter.
The conventional wisdom about dark matter is that it is composed of WIMPs, massive particles that hardly interact with particles of ordinary matter. And yet, despite the hundreds of studies throughout the years, dark matter has not been confirmed.
The concept of dark matter plays an important role in modern astrophysics and cosmology – it makes it relatively easy to explain the rotation curves of galaxies, gravitational lensing, and the observed expansion rate of the Universe while remaining a self-sufficient theory that does not require the selection of many numerical coefficients.
Direct experimental evidence of the existence of dark matter – for example, the scattering of its constituent particles by particles of the Standard Model – has not yet been found. So far, physicists have to limit themselves to indirect evidence of the gravitational interaction of dark and ordinary matter and improve detectors.
In the past, we have written about new studies on dark matter and black holes on many occasions – results of new studies come up literally every month if not every week. And now, a scientific team has suggested that these two celestial phenomena may be the same thing, in a certain case.
Scientists have reached the conclusion that dark matter could be made from primordial black holes. Explained – these are black holes that were created shortly after the Big Bang. The scientific team analyzed the data from two ripples in space-time that occurred after two individual collisions between black holes and neutron stars or larger black holes.
The connection between primordial black holes and dark matter
Primordial black holes compare favorably with other candidates for the role of dark matter in that they allow solving the so-called ” cuspy halo problem”. It consists in the fact that computer models of the evolution of galaxies promise a sharp increase in the density of dark matter near its center (sharp peak, cusp), while the rotation curves observed in reality indicate rather a constant distribution (that is, the core, core).
Models, where dark matter consists of primordial black holes, do not show such peaks. In addition, the motion of stars within a galaxy surrounded by primordial black holes is slightly different from the motion of stars in other dark matter models.
And here is another problem – primordial black holes are just as hypothetical as dark matter. Both have not yet been officially discovered or confirmed but both fit perfectly in the explanation of processes and phenomena in the universe that the standard model cannot explain.
What does the new study suggest?
Numerous simulations and calculations have confirmed that if primordial black holes existed in the early universe, the largest of them could still exist in the modern universe.
One theory suggests that neutron stars could attract dark matter to the extent that both collapse into a black hole. An alternative suggests that neutron stars could merge with primordial black holes. These two would then continue to attract dark matter until the neutron star disappears completely, leaving only a black hole behind.
The scientific team analyzed dozens of gravitational wave detections only to find that two from 2019 correspond to the right characteristics of primordial black holes. This does not confirm that they are, in fact, there are several other possible explanations, but this study could lead to important tests that will explain both primordial black holes and how they could be related to dark matter. Furthermore, results may confirm that dark matter is made from black holes.
As usual, this is only the initial study and it will take years of observation and data collection before scientists could answer this question. Nevertheless, this is a big step forward.
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• Argüelles, C., Díaz, M., Krut, A., & Yunis, R. (2020, December 31). On the formation and stability of fermionic dark matter haloes in a cosmological framework.
• Metcalfe, T. (2021, April 05). Dark matter could be made of black holes from the beginning of time.
• Royal Astronomical Society. (2021, February 24). New study suggests supermassive black holes could form from dark matter.