Dark matter and black holes
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Dark Matter and Black Holes: Fundamental Connections
Dark Matter Properties and Theoretical Origins
Dark matter is a mysterious substance that makes up about six times more of the universe than ordinary matter. It does not emit light or radiation and interacts mainly through gravity, making it invisible to telescopes. Some theories suggest dark matter could be made of exotic particles, such as magnetically charged neutrinos, which would require a major shift in our understanding of physics, including a reversal of Maxwell’s laws to allow for magnetic charges instead of electric ones.
Primordial Black Holes as Dark Matter Candidates
A leading idea is that primordial black holes (PBHs), which formed from density fluctuations in the early universe, could make up some or all of the dark matter. This idea has gained traction, especially after the detection of gravitational waves from black hole mergers by LIGO and Virgo, which showed the existence of black holes with masses in the range expected for PBHsGreen2024Villanueva-Domingo2021Carr2020+4 MORE. PBHs could be stable over cosmic timescales and, depending on their mass, might avoid current observational constraints, making them viable dark matter candidatesCarr2020Inomata2017Bai2019+2 MORE.
Black Holes’ Influence on Dark Matter Distribution
Black holes, especially supermassive ones at the centers of galaxies, can strongly affect the distribution of dark matter around them. The gravitational pull of black holes can create dense regions of dark matter, known as cusps, spikes, or mounds, and can even form structures called gravitational atoms. The interaction between black holes and dark matter can also influence the evolution of black hole binaries, as energy is transferred between them through a process called dynamical friction.
Observational Probes and Gravitational Waves
The abundance and properties of PBHs as dark matter are constrained by various observations, including gravitational lensing, cosmic microwave background measurements, and the search for signals from Hawking radiation. Gravitational wave detectors like LIGO, Virgo, and future observatories may provide further evidence by detecting signals from PBH mergers or from the gravitational wave background produced during their formationGreen2024Villanueva-Domingo2021Carr2020+3 MORE. Recent data from the NANOGrav collaboration hints at a gravitational wave background that could be explained by the formation of PBHs, supporting the idea that they could make up all of the dark matter.
Exotic Scenarios: Magnetic Neutrinos and Extremal Black Holes
Some more speculative ideas propose that dark matter could be made of particles created inside black holes, such as sterile magnetic neutrinos, which escape from black holes and become dark matter. Another possibility is that nearly extremal black holes, which are stable due to their charge and mass, could survive from the early universe and make up dark matter. These black holes would be difficult to detect directly but could produce observable signals during rare merger events.
Conclusion
Research shows a strong connection between dark matter and black holes, especially primordial black holes, which remain a leading candidate for dark matter. Black holes can shape the distribution of dark matter, and new observations—especially gravitational waves—are providing important clues. While some theories suggest exotic particles or processes inside black holes could explain dark matter, primordial black holes offer a compelling and testable link between these two cosmic mysteriesBagdoo2020Bertone2024Green2024+7 MORE.
Sources and full results
Most relevant research papers on this topic
What Connects Dark Matter and Black Holes?
Dark matter is composed of magnetically charged neutrinos and is derived from black holes, mainly from active supermassive black holes, through a reversal of Maxwell's laws and sterile magnetic neutrinos crossing the horizon to the outside.
A Brief Review on Primordial Black Holes as Dark Matter
Primordial black holes are a potential candidate for dark matter, with their formation, abundance, and signatures potentially impacting the evolution of the Universe and the formation of structures.
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