Tiny, nearly undetectable primordial black holes could be one of the mysterious sources of mass that contribute to dark matter. There are significant limits to their lifespan in open space, but in recent years, astrophysicists have wondered: what if these black holes are in the core of neutron stars?
Gradually, those black holes would enlarge the neutron star and devour it from within. These hypothetical systems have yet to be verified, but a new pre-print article, published on arXiv and yet to be peer-reviewed, has calculated how long this devouring would take.
This, in turn, could be used to analyze the current population of neutron stars to narrow down the nature of black holes considered dark matter candidates, whether primordial, dating back to the Big Bang, or black holes that formed inside stars. neutron. .
Although we do not know what dark matter is, it is quite fundamental to our understanding of the Universe: there is simply not enough matter that we can directly detect, normal matter, to account for all gravity. In fact, there is so much gravity that scientists have calculated that roughly 75 to 80 percent of all matter is dark.
There are a number of candidate particles that could be dark matter. The primordial black holes that formed just after the Big Bang are not one of the main candidates, because if they were above a certain mass we would have already noticed them; but, below that mass, they would have evaporated through the emission of Hawking radiation much earlier.
Black holes, however, are an attractive candidate for dark matter: They, too, are extremely difficult to detect if they are simply in space doing nothing. So astronomers keep looking for them.
One idea that has recently been explored is the endoparasitic black hole. There are two scenarios for this. One is that primordial black holes were captured by neutron stars and sink to the core. The other is that dark matter particles are captured inside a neutron star; if conditions are favorable, they could coalesce and collapse into a black hole.
These black holes are small, but they would not remain so. From their cozy position, installed inside the neutron star, these small black holes would parasitize their host.
The team of physicists from Bowdoin College and the University of Illinois at Urbana-Champaign calculated the accretion rate, that is, the rate at which the black hole would devour the neutron star, for a range of black hole mass ratios, three to nine. orders of magnitude less massive than the host neutron star.
Neutron stars have a theoretical upper mass limit of 2.3 times the mass of the Sun, so the masses of black holes would extend into the range of dwarf planets.
For a non-rotating neutron star that hosts a non-rotating black hole, the accumulation would be spherical. Based on accretion rates calculated by the team, black holes as small as 10-twenty-one times the mass of the Sun would completely accumulate a neutron star within the lifespan of the Universe.
This suggests that primordial black holes, from the beginning of the Universe, would have fully accumulated their host neutron stars before now. These timescales are in direct conflict with the ages of ancient neutron star populations, the researchers said.
“As an important application, our results corroborate arguments that use the current existence of neutron star populations to limit the contribution of primordial black holes to the dark matter content of the Universe, or that of dark matter particles that can form holes. blacks in the center of neutron stars after they have been captured, “they wrote in their article.
So the result is another blow to primordial black holes; but it doesn’t completely rule out endoparasitic black holes. If there are globes of dark matter particles floating in space and absorbed into neutron stars, they could collapse into black holes and turn neutron stars into black hole things even as you read this sentence.
And that is incredible.
The team article has been published on arXiv.