Small but undetectable primary black holes can be one of the mysterious sources of mass that contribute to dark matter. There are significant limits to their lifespan in outer space, but in recent years astrophysicists have asked: what if these black holes are at the core of neutron stars?
Gradually, such black holes would accumulate in the neutron star, engulfing it from within. These hypothetical systems are yet to be tested, but a new paper with preprint, published on arXiv and pending review, estimates how long this takeover will take.
This in turn could be used to analyze the current population of neutron stars to limit the nature of black holes considered a candidate for dark matter ̵
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 of gravity. In fact, there is so much gravity that scientists have estimated that approximately 75 to 80 percent of all matter is dark.
There are a number of candidate particles that can be dark matter. The primary black holes formed immediately after the Big Bang are not one of the leading candidates, because if they were above a certain mass, we would already notice them; but beneath that mass they would have evaporated by Hawking radiation long before now.
However, black holes are an attractive candidate for dark matter: they are also extremely difficult to detect if they just hang in space and just do nothing. So astronomers keep looking for them.
One idea that has been explored recently is the endoparasitic black hole. There are two scenarios for this. One is that the primary black holes were captured by neutron stars and sank down to the nucleus. The other is that particles of dark matter are trapped inside a neutron star; if conditions are favorable, they can merge and collapse into a black hole.
These black holes are small, but they will not stay that way. From their cozy position, located inside the neutron star, these small black holes would parasitize on their host.
The team of physicists from Bowdoin College and the University of Illinois at Urbana-Champaign calculated the degree of accumulation – ie. the speed at which the black hole will absorb the neutron star – for a number of mass ratios of the black hole, three to nine orders of magnitude less massive than the host of the neutron star.
Neutron stars have a theoretical upper limit on the mass of 2.3 times the mass of the Sun, so the masses of black holes will extend down to the range of the dwarf planets.
For a non-rotating neutron star with a non-rotating black hole, the accumulation will be spherical. At the growth rates calculated by the team, the black holes are only 10-21 times the mass of the Sun would give a completely neutron star within the life of the universe.
This suggests that the original black holes, from the beginning of the universe, had been fully accredited by their host neutron stars before. These terms are in direct conflict with the epochs of populations of old neutron stars, the researchers said.
“As an important application, our results confirm arguments that use the current existence of neutron star populations to limit either the contribution of primary black holes to the content of dark matter in the universe or that of dark matter particles that can form black holes. at the center of neutron stars after they have been captured, “they wrote in their report.
So the result is another blow to the primary black holes; but does not completely rule out endoparasitic black holes. If there are globes of dark matter particles that float in space and are bent into neutron stars, they can collapse into black holes and turn neutron stars into things from the black hole, even as you read this sentence.
And that’s terribly great.
The team’s report is published on arXiv.