For the first time, the size of the heaviest known neutron star has been calculated. It is called J0740 for short, and it is more than twice the mass of our Sun. Yet it is only 25 kilometers in diameter and is about 3,600 light years from Earth.
A neutron star is what remains of a star that has exploded. It is incredibly dense, but not enough to turn into a black hole.
“A neutron star is a dead star. Neutron stars are formed when massive stars, that is, somewhat heavier than our Sun, reach the end of their life and become supernovae. And the cores of those stars collapse in on themselves. In the case of the heaviest stars, this collapse is absolutely unstoppable and produces black holes, from which not even light can escape. Slightly lighter stars produce neutron stars, which are actually rather tiny, ultra-dense planets. And they are so dense that a teaspoon of neutron star material would weigh as much as Mount Everest.”Says Anna Watts, professor of astrophysics at the University of Amsterdam.
It was discovered in 2019 using the “Neutron star Interior Composition Explorer” or NICER telescope, located on the International Space Station, and challenges theories about what is at the heart of neutron stars. J0740 is not as small as you might expect, which calls into question some of the more plausible models
“Some of the models that existed previously said that they could actually be quite small, even if they contained a huge amount of matter. But when we measured the star, we realized that it is not as small as we might have expected,” he continues Watts.
And the researchers want to know why the heaviest ones turn into black holes and the lightest ones turn into neutron stars: “This is a really hot topic right now because we have colleagues who are also doing gravitational wave analysis, trying to get to this from a different point and finding smaller and smaller black holes, and we are trying to figure out where the limit is to become. in a neutron star. And at some point, there is a line, beyond which something has to become a black hole, “concludes the astrophysicist.