New models of neutron stars show that their tallest mountains may be only fractions of a millimeter high, due to the enormous gravity of the ultra-dense objects, according to research presented this Friday at the 2021 National Astronomy Meeting.
Neutron stars are one of the densest objects in the Universe, since they weigh as much as the Sun, but they are only about 10 km wide, a size similar to that of a large city.
Due to their compactness, neutron stars exert an enormous gravitational pull, approximately one billion times greater than that of the Earth.to. This squashes all the elements on the surface down to minuscule dimensions, which means that the stellar remnant is an almost perfect sphere.
Although they are billions of times smaller than on Earth, these deformations of a perfect sphere are known as mountains. The team responsible for the work, led by PhD student Fabian Gittins from the University of Southampton, UK, used computer models to build realistic neutron stars and subject them to a series of mathematical forces to identify how mountains are created.
The team also studied the role of ultra-dense nuclear matter in the support of mountains, and found that the largest mountains produced were only a fraction of a millimeter high, a hundred times less than previous estimates.
Fabian explains that “Over the last two decades, there has been a lot of interest in understanding how big these mountains can be before the crust of the neutron star breaks down, and the mountain can no longer sustain itself. ”
Previous work has suggested that neutron stars can sustain deviations from a perfect sphere of up to a few parts in a million., which implies that the mountains could be as big as a few centimeters. These calculations assumed that the neutron star was under such stress that the crust was about to break apart at every point. However, new models indicate that such conditions are not physically realistic.
Fabian adds that “these results show how neutron stars are really remarkably spherical objects. Furthermore, they suggest that observing gravitational waves from rotating neutron stars may be even more difficult than previously thought. ”
Although they are individual objects, due to their intense gravitation, rotating neutron stars with slight deformations should produce waves in the fabric of spacetime known as gravitational waves.
Gravitational waves from the rotations of individual neutron stars have not yet been observed, although Future advances in extremely sensitive detectors, such as the advanced LIGO and Virgo, could be the key to probing these unique objects.