Particles of high-energy radiation may be coming from dormant black holes
The universe is full of “soft” megaelectronvolt gamma rays and high-energy neutrinos. However, their resources are still elusive in most cases. The Japanese team suggests that it could be dormant supermassive black holes, which sometimes peel something off, but it’s not a dazzling celestial show, so we practically don’t see them in our telescopes.
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Supermassive black holes can be inconspicuous. Credit: NASA, ESA, and D. Coe, J. Anderson, and R. van der Marel (STScI).
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The universe appears to be filled with sparse radiation of gamma photons of MeV energies, or “soft” gamma rays, and neutrinos of PeV energies. However, the origin of these high-energy particles remains a mystery in the vast majority, despite considerable efforts. Photons of gamma radiation and neutrinos are not very rare in space. High-energy gamma radiation is sometimes detected even in the TeV region, and we also occasionally detect high-energy neutrinos. Such radiation probably comes from natural cosmic particle accelerators, such as the remnants of supernovae or black holes voraciously devouring matter.
Shigeo Kimura. Kredit: Tohoku University.
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However, if we subtract such sources of high-energy radiation, we still have a lot of gamma radiation of slightly lower energies, ie the mentioned gamma photons with energies in megaelectronvolts, as well as a lot of high-energy neutrinos, the origin of which we do not know. Shigeo Kimura of Tohoku University in Japan and colleagues suggest that these high-energy particles come from a somewhat unexpected source – supermassive black holes that are not stormily active but also not completely dormant.
A well-driven supermassive black hole cannot be overlooked. Credit: ESO / M. Corn knife.
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A well-driven supermassive black hole, which hungrily swallows matter, can hardly be overlooked. It illuminates its entire galaxy and is visible over vast distances thanks to dazzling radiation across the wavelength spectrum. But not all supermassive black holes are so active. Our domestic supermassive black hole is more like a very sleepy panda than a raging tiger with a singularity in the chest.
According to Kimur’s team, gamma rays about the energies in the MeV region that flood the universe, as well as the amount of neutrinos, come from supermassive black holes, which are active but so few that they are completely invisible in our telescopes. When such dormant supermassive black holes consume a little matter, a plasma of billions of degrees is still formed around them.
Such a plasma is capable of generating megaelectronvolt gamma rays. In the same way, protons are accelerated to such an extent that high-energy neutrinos are formed during interactions with other particles. According to the Japanese team, dormant supermassive black holes are therefore a hot favorite for a significant source of high-energy background radiation.
Literature
Nature Communications 12: 5615.
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