Using a radio telescope in South Africa, researchers have discovered an object heavier than the heaviest known neutron stars, but lighter than the lightest black holes known to us. This creates great excitement.
Because what exactly is this being? Scientists are left without an answer, as they say in the magazine Sciences Published study. But whatever additional research reveals; It's an exciting discovery anyway.
Pulsar
Astronomers have discovered the still somewhat mysterious object in the globular star cluster NGC 1851, about 40,000 light-years from Earth. A globular star cluster is a massive collection of (old) stars that are so densely packed that they interact with each other on a very regular basis. During observations with the MeerKAT radio telescope, researchers encountered a pulsar in this globular star cluster: a rapidly rotating neutron star. They soon found evidence that this pulsar was not alone; There was something in orbit around the pulsar.
What is the heaviest neutron star or the lightest black hole?
Further analysis then revealed that the object in question had an appreciable mass; It was heavier than the heaviest neutron star and lighter than the lightest black hole. This raises an interesting question. Have researchers now discovered the heaviest neutron star ever or have they encountered the lightest black hole ever? Or did they find a version of it that is still unknown to us?
Neutron star versus black hole
A neutron star is actually the collapsed core of a dead massive star. The collapsing core has so much gravity that all the matter is compressed into neutrons. For this reason it is called a neutron star. This neutron star has about the same mass as our Sun, but is only 20 to 40 kilometers in diameter. If such a neutron star became too heavy – for example because it collided with another star and merged – it could collapse further. It is believed that it will then turn into a black hole: an object with such intense gravity that not even light can escape from it. But when is a neutron star too heavy and therefore doomed to turn into a black hole? Scientists believe that this limit is about 2.2 solar masses. In other words, if a neutron star were 2.2 times more massive than our Sun, it would collapse into a black hole. But there's one problem: the lightest black holes that we suspect formed as a result of the collapse of stars are much heavier, about five times heavier than our Sun. It indicates that we are overlooking something; Something that lies between the heaviest neutron stars and the lightest black holes in terms of mass. Researchers now believe they have found such an object.
What exactly it is remains a mystery at the moment. But both options are equally exciting for astronomers. “The system consisting of a pulsar and a black hole is interesting for testing theories of gravity,” says researcher Ben Stubbers. According to Stubbers, a heavy neutron star could provide new insights into how matter behaves under extreme conditions — that is, densely packed into such a neutron star. Colleague Arunima Dutta agrees. “We're not done with this system yet. Discovering the true nature of this companion (of the pulsar, ed.) will be a turning point in our understanding of neutron stars, black holes, and whatever else might lurk in that gap between the heaviest neutron stars and the lightest black holes.”
