A new model presented by physicists raises the possibility that the Universe could be filled with ultralight primordial black holes that don’t die.
Formed during the earliest moments of the Universe, primordial black holes are hypothetical objects.
The fate of ultralight black holes depends on whether or not evaporation stops at or around the Planck scale. If evaporation stops, the general expectation is that a population of Planck-scale will be left over, possibly including a significant fraction of electrically charged relics.
If evaporation does not stop, a runaway “explosion” would occur, with significant and potentially detectable high-energy emissions.
Researcher Stefano Profumo reviewed both possibilities, with an emphasis on current status and future detection prospects.
According to the models, they formed from micro-fluctuations in matter density and spacetime to become sand grain-sized mountain-massed black holes.
Although scientists have never detected primordial black holes, they have all the necessary properties of dark matter, such as not emitting light and the ability to cluster around galaxies. If they exist, they could explain most of dark matter, according to the paper in Universe Today.
Ultralight black holes may radiate away completely
In previous studies, most primordial black hole candidates have been ruled out. But the new model focuses on ultralight primordial black holes.
Profumo pointed out that there could be three possibilities. The first will be that the ultralight black holes will radiate away completely and end as a brief flash of high-energy particles.
In the second possibility, a complete evaporation could be prevented by any mechanism and the black hole will reach some kind of equilibrium state.
In the third option, the equilibrium state causes the event horizon to disappear, leaving an exposed dense mass known as a naked singularity.
Objects might have a net electric charge
According to Profumo, for the second and the third possibility, the objects might have a net electric charge.
The most likely fate of primordial black holes is either complete evaporation in a runaway process, or the formation of Planck-scale relics.
There exist several arguments for the latter possibility, but the first is not excluded, as physics at the Planck scale is largely unknown.
In the last two possibilities, the equilibrium would be reached around the Planck scale and the remnants would be proton sized but with much higher masses. But if these remnants are electrically neutral, it won’t be possible to detect them.
However, if the particles do have a charge, they will be easily detectable by next generation of neutrino detectors.
While no evidence of exploding primordial black holes has emerged so far, perhaps the most promising path ahead is to use the Interplanetary Gamma-Ray Burst Timing Network.
Exploding primordial black holes leaving a visible imprint are slated to be much closer than, approximately, 1% , as opposed to cosmologically-distant GRBs.
