 |
| The sun and other stars might look and act differently if they held black holes (Credit: Nixx Photography/ Shutterstock) |
Stars could have tiny black holes hiding inside them that were formed during the big bang. This idea, first dreamed up by Stephen Hawking, might also explain the origins of dark matter, researchers have found.
In 1971, physicist Hawking was looking at a problem involving an apparent lack of high-energy particles coming from the sun. He wondered whether this solar neutrino problem could be solved if the sun hosted a small black hole that was formed at the beginning of the universe, a so-called primordial black hole. Some astronomers took the idea further, but when the solar neutrino problem was solved in 2001, interest in black hole-hosting stars died out.
Now, Earl Bellinger at the Max Planck Institute for Astrophysics in Germany and his colleagues have revived the idea as a possible explanation for dark matter, and calculated what effects primordial black holes of different masses might have on the evolution of their host star.
For our sun, Bellinger and his team first ruled out black holes with masses smaller than a typical asteroid because these wouldn’t grow or have measurable effects. They also ruled out those larger than the sun itself, as these would rapidly eat up their star. This left black holes with about the mass of the planet Mercury or larger, which would accrete matter and grow, but not too quickly.
Such a black hole that is sucking up the sun’s fuel from the inside would make the star grow by producing powerful light that pushes out its outer layers. This would, over millions of years, cool the temperature below that needed for nuclear fusion, which is the reaction that keeps a star stable, says Bellinger.
The cooling effect would cause the entire star to become tumultuous and chaotic, like a pot of boiling water. It would ultimately turn into a rare kind of unusually cool star called a red straggler. A black hole at the centre of a red straggler would also make it pulsate in a unique way – a primordial black hole signature that Bellinger hopes to now look for in the 500 or so red stragglers we currently know of.
The fact that black hole-hosting stars would pulsate in this way means it is unlikely that our sun is one, because we would have already seen this signature, but it isn’t impossible.
A black hole small enough to create a hard-to-spot signature could still affect the sun’s evolution, says Bellinger. Such a black hole would effectively lower the sun’s temperature, saving Earth from being engulfed by our star when it eventually runs out of fuel and turns into a normal red giant. However, it would still get hot enough to boil off Earth’s oceans and kill all life.
If we do find other stars hosting primordial black holes, then they could help explain dark matter, which is what is thought to cause the otherwise unexplained gravitational effects we see in the universe, such as galaxies rotating faster than expected based on the influence of visible matter alone. If black holes are hiding within stars, their extra mass could go some way to explaining this effect, says Bellinger.
Although black hole-hosting stars could theoretically explain dark matter, says Paulo Montero-Camacho at Tsinghua University in China, there is a large assumption in the work that has yet to be proven, which is that stars can grab primordial black holes in the first place. “It’s difficult for a star to actually capture primordial black holes, since they are so tiny and move so fast,” he says.
Journal reference
The Astrophysical Journal DOI: 10.3847/1538-4357/ad04de
0 Comments