Neutron stars have mountains less than a millimeter high

A team of astrophysicists recently used new models of neutron stars to map mountains – tiny elevated areas – on the otherwise perfectly spherical structures of stars. They found that the largest deviations were still extremely small due to the intense gravitational pull, pointing less than a millimeter high.

Neutron stars are the dead nuclei of once huge stars that collapsed on themselves. They are the densest objects in the Universe apart from black holes. They are called neutron stars because their gravity is so intense that the electrons in their atoms collapse into the protons, forming neutrons. They are so compact that they pack a mass greater than that of our Sun in a sphere no larger than a city.

The evaluation by the team of “mountains” on these neutron stars comes into play. of them papers currently hosted on the arXiv preprint server; together, newspapers estimate the size of these mountains. The team’s results are presented today at the National Astronomical Meeting of the Royal Astronomical Society.

“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,” said Fabian Gittins, astrophysicist at the University of Southampton. and lead author of both articles, in a Royal Astronomical Society Press release.

Previous work has indicated that mountains of neutron stars could be a few inches tall, several times larger than what the recent team has valued. Previous calculations assumed that the neutron star would experience such large bumps on its surface if it was stretched to its limits, like Atlas holding the world. But recent modeling find that previous calculations are unrealistic behavior to expect from a neutron star.

“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,” Gittins explains in the press release.

Previous work has suggested that neutron stars can withstand deviations from a perfect sphere up to a few parts in 1 millions, which implies that the mountains could reach a few centimeterss. These calculations assumed that the neutron star was deformed such that the crust was about to shatter at any point. however, new models indicate that such conditions are unlikely.

“A neutron star has a fluid core, an elastic crust and, in addition, a thin fluid ocean. Every region is complicated, but let’s forget the fine print ”, Nils Andersson, co-author of the two papers and astrophysicist at the University of Southampton, said in an email. “What we have done is create models that connect these different regions in the right way. This allows us to tell when and where the elastic crust first breaks. Previous models assumed that the stress was maximum at all points at the same time, which (in our opinion) leads to mountains estimated to be a little too large.

These crustal yields would mean energy from the mountain would be released into a larger area of ​​the star, Andersson said. Although based on computer models, the crustal shifts would not be “dramatic enough to cause the star to collapse, as the region of the crust involves material of fairly low density,” Andersson said.

Intriguing questions remain. It is possible, said Andersson, that after an initial crustal break, mountains larger than those modeled by the team could occur due to the material flow through the surface of the star. But even these mountains would be a lot smaller than a molehill, compressed by the immense gravity of the stars.

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