Sat. Jan 28th, 2023
Hypothetical black holes could eat neutron stars

Immediately after the Big Bang, the matter of the Universe was incredibly dense and rippled with random fluctuations. Is it possible that some parts of it reached densities high enough to collapse into black holes?

The idea of ​​primordial black holes has been buzzing in theoretical circles for some time, in part because they could provide much of the dark matter that seems to dominate the large-scale structures of the Universe. But testing their existence requires some sort of consequence that we might discover, and the theorists have largely fallen short of that. But now a team of three physicists is signing up Physical assessment letters has come up with a rather intriguing corollary: these black holes could gobble up a neutron star that, under the right conditions, would spew out heavy elements.

Truth or consequences

There are two things that can distinguish primordial black holes from those formed by the collapse of a massive star. One is that they can have almost any mass, from less than the mass of a star to thousands of times heavier than anything formed during a supernova. The heavier end of the spectrum is attractive, as it could explain how supermassive black holes appeared so soon (in astronomical terms) after the birth of the universe.

The second feature is that primordial black holes were present early in the history of the universe. The influence of dark matter is evident long before the Universe formed stars, which appear to be a necessary precursor to black holes that formed after the Universe began to spread. Being present early, primordial black holes could account for a significant percentage of dark matter, though several studies have placed some limitations on how much.

The problem is that we can’t examine either issue in enough detail to know if primordial black holes exist. So while these objects remain physically plausible, there are no implications for their existence that we can look for in the current universe.

Unless, of course, the new newspaper is right. In it, the authors describe the rather unusual consequences of a primordial black hole colliding with an equally exotic object: a rapidly spinning neutron star.

Meet the neutrons

Imagine a sphere the width of Manhattan spinning so fast that it spins in milliseconds. Now drop a black hole on it. What is happening?

That is the fundamental question the paper addresses. Black holes have fundamental limits on how fast they can gobble up matter, meaning the neutron star wouldn’t be immediately destroyed even if the two made contact. Instead, the black hole’s slow feeding would allow it to settle in the center of the neutron star and slowly devour it from within.

As the black hole continued to feed, the neutron star would contract. Conservation of angular momentum would then make it spin faster – and remember this thing is already moving blindingly fast. Eventually, it’s possible to spin one of these fast enough for the surface near the equator to reach escape velocity. As much as 10 percent of the Sun’s mass of neutron-rich material would be flung into space.

Obviously, a mass of neutrons is not stable under normal conditions, and this material would quickly undergo reactions to convert itself into atoms. But the authors conclude that the results would be heavy, neutron-rich atomic nuclei. And that’s interesting. Heavier nuclei are believed to be formed by something called the r-process, named after the rapid accumulation of neutrons. This requires them to be bombarded with neutrons so quickly that the atom does not have time to rearrange itself in response to one before a second has been absorbed. When the rearrangement reaction finally takes place, there are enough protons and neutrons around to form a heavy element.

Imagine a sphere the width of Manhattan spinning so fast that it spins in milliseconds. Now drop a black hole on it. What is happening?

While it’s widely believed that a supernova creates conditions for the r-process to take place, scientists are still trying to figure out if that’s really the case. But the paper inside Physical assessment letters states that we do not need a supernova to form these heavy elements. It argues that the distribution of heavy elements in the universe is roughly in line with what one would expect from the original black hole/neutron star production pathway.

In fact, the authors claim that this mechanism could solve all sorts of astronomical mysteries, from the mechanism for producing non-repeating fast radio bursts, to kilonovas, to the production of antimatter in our galaxy. In addition, the black holes themselves could account for about 10 percent of the universe’s dark matter.

But the nice thing is that it makes a prediction. If we observed a nearby kilonova or fast radio burst, gravitational wave detectors could detect a disturbance, but that disturbance would not be accompanied by the normal waves produced by black holes merging into each other – for obvious reasons, since the black hole is already in its partner. All we have to do is wait a few years for a few more detectors to come online, then wait however long it takes for one of those events to occur within their detection range.

Physical assessment letters2017. DOI: 10.1103/PhysRevLett.119.061101 (About DOIs).

By akfire1

Leave a Reply

Your email address will not be published.