December 4, 2023

Primordial black holes: how light could they be?

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But why should black holes form this way? When it comes to stellar black holes, it’s fairly straightforward: they form when a star collapses at the end of its life under the gravitational force of its own mass, thus compressing significantly. However, the force of a star is not necessarily required to condense matter. At the beginning of the universe, when there were no objects such as stars or galaxies, matter was not evenly distributed. Perhaps there were regions in space where random fluctuations caused the mass density to be large enough to collapse into black holes. The faster it happens after the Big Bang, the less mass it requires.

However, we know – thanks in part to the work of Stephen Hawking – that the less massive a black hole is, the shorter its life. The mountain-massive black hole would have dissolved in just over a billion years due to Hawking radiation. So in today’s world we will not find such things. But it’s also possible that there were primordial black holes that were created at just the right time and have now been completely wiped out. Since this last stage occurs very explosively, we can observe this theoretically. But so far we have not discovered any clear evidence of this.

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Explanation of dark energy

The existence of primordial black holes may clarify some open questions in astronomy. If these objects had been around since the beginning of the universe, their gravitational pull could have played an important role in the subsequent formation of the first stars and galaxies. Primordial black holes may be a relevant component of dark matter. If, surprisingly, we find a primordial black hole with a mass too small to survive to this day, it would be a clear indication that the force of gravity works very differently on small scales than we previously thought.