Mountains of several millimeters on neutron stars

New models of neutron stars show that their tallest mountains may be as small as fractions of a millimeter, due to the enormous gravity on ultra-dense objects. The research is presented today at the 2021 National Astronomy Meeting.

Neutron stars are among the densest objects in the Universe: they weigh about as much as the Sun, but are only about 10 km in diameter – the size of a large city.

Due to their compactness, neutron stars have a huge gravitational pull about a billion times stronger than Earth. This reduces every feature of the surface to minuscule dimensions and means that the stellar remnant is an almost perfect sphere.

If they are billions of times smaller than on Earth, these deformations from a perfect sphere are nevertheless called mountains. The team behind the work, led by University of Southampton student Ph.D. Fabian Gittins, used computer modeling to build realistic neutron stars and subject them to a range of mathematical forces to identify how mountains are created.

The team also studied the role of ultra-dense nuclear matter in supporting mountains and found that the largest mountains produced were only a fraction of a millimeter high, a hundred times smaller than previous estimates.

Fabian comments: “Over the past two decades there has been a lot of interest in understanding how big these mountains can be before the neutron star’s crust breaks and the mountain can no longer be. supported. “

Previous work has suggested that neutron stars can withstand deviations from a perfect sphere of up to a few parts in a million, implying that mountains could be as large as a few centimeters. These calculations assumed that the neutron star was deformed such that the crust was about to shatter at any point. However, the new models indicate that such conditions are not physically realistic.

Fabian adds: “These results show just how remarkably spherical neutron stars really are. Additionally, they suggest that observing the gravitational waves of spinning neutron stars may be even more difficult than previously thought. before. “

Although these are unique objects, due to their intense gravitation, spinning neutron stars with slight distortions are expected to produce ripples in the fabric of space-time known as gravitational waves. . Gravitational waves from the rotations of single neutron stars have yet to be observed, although future advances in extremely sensitive detectors such as advanced LIGO and Virgo may hold the key to probing these unique objects.