Neutron stars are the densest objects in the universe. In something only as big as a city, there is more compressed mass than the Sun. This has some peculiar consequences – including how smooth they are. The gravitational pull of such an object is so high and its crust so hard that you wouldn’t get “mountains” on its surface higher than a millimeter, new research suggests.
The results, presented at the National Astronomy Meeting 2021, come from new models that tried to create more realistic simulations of what neutron stars are like. In particular, the team was interested in the tiniest deformations of the neutron stars’ surface – known as mountains, despite being minuscule – finding that they were a hundred times smaller than previously estimated.
"For the past two decades, there has been much interest in understanding how large these mountains can be before the crust of the neutron star breaks, and the mountain can no longer be supported," Fabian Gittins, a graduate researcher at the University of Southampton and leader of the research team, said in a statement.
The forces involved in these objects are truly mind-boggling. Simulations have suggested that the surface of a neutron star is 10 billion times more rigid than steel. Previous models suggested that these mountains could be up to a few centimeters tall, suggesting that this crust was close to breaking at every point. But the new work is arguing that this assumption is not backed up by physically realistic scenarios.
Neutron stars are really smooth. If we were to blow a neutron star to the size of the Earth, these mountains wouldn’t be taller than half a meter (20 inches). You don’t get smoother than a neutron star.
"These results show how neutron stars truly are remarkably spherical objects. Additionally, they suggest that observing gravitational waves from rotating neutron stars may be even more challenging than previously thought," Fabian added.
The material of which neutrons stars are made is an incredible state of matter. It is 100 trillion times denser than any material on Earth, and it is expected to be organized in peculiar structures called nuclear pasta. You have gnocchi, spaghetti, waffles, and lasagne, but also antignocci and antispaghetti.
These structures are known from simulations, but astronomers hope that we might soon have more direct observations of such structures. Collisions between neutron stars have been detected by the gravitational waves observed across the world, and it might be possible in the future to find out what exactly goes on in these objects.