Neutron stars have mountains that are less than a millimeter high

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The artist's depiction of a neutron star.

The artist’s depiction of a neutron star.
Picture: ESO / L. Sidewalk

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

Neutron stars are the dead nuclei of once huge stars that have crashed on themselves. They are the densest objects in space, except for black holes. They are called neutron stars because their gravity is so intense that electrons in their atoms collapse u protons, forming neutrons. They are so compact to pack a mass greater than the mass our Sun into a sphere no wider than the city.

The team’s assessment of the “mountains” on these neutron stars is included two papers currently hosted on the arXiv overprint server; together, the leaves estimate how large these mountains can be. The results of the team are presented today at the National Astronomical Meeting of the Royal Astronomical Society.

“In the last two decades, there has been a lot of interest in understanding how big these mountains can be before the neutron star crust breaks through and the mountain can no longer be supported,” said Fabian Gittins, an astrophysicist at the University of Southampton and lead author of two papers at the Royal astronomical society Media Release.

Previous work has shown that the mountains of neutron stars could be several centimeters high – many times larger than what the recent team has estimated. Earlier calculations assumed that a neutron star would withstand such large protrusions on its surfaces tense to its limits, like an Atlas holding the world. But recent modeling found that earlier calculations are unrealistic behavior expected of a neutron star.

Cancer Nebula, imaged by the Hubble Space Telescope.  The neutron star is located in the heart of the structure formed by the supernova.

“In the last two decades, there has been a lot of interest in understanding how big these mountains can be before the crust of a neutron star breaks through and the mountain can no longer be supported,” Gittins explains in a statement.

Previous work has suggested that neutron stars can withstand deviations from a perfect sphere to several parts in 1 million, which implies that the mountains could be as large as a few centimeterss. These calculations assumed that the neutron star was strained in such a way that the crust was close to bursting at all times. However, new models indicate that such conditions are unlikely.

“A neutron star has a fluid nucleus and an elastic crust, and on top of that a thin fluid ocean. Every region is complicated, but let’s forget about the small print, ” Nils Andersson, co-author of both papers and an astrophysicist at the University of Southampton, said in an email. “What we have done is to build models that connect these different regions in the right way. This allows us to tell when and where the elastic crust first bursts. Previous models have assumed that the effort is maximal at all points simultaneously and this leads to (we consider) estimated mountains that are slightly too large. “

These crust yields would mean that energy from the mountain would be released into a larger area of ​​the star, Andersson said. Although based on computer models, the shifts in the crust “would not be dramatic enough for the star to collapse, because the area of ​​the crust includes matter of fairly low density,” Andersson said.

Intriguing questions remain. There is a possibility, Andersson said, that after the first crusting, larger mountains than those modeled by the team could appear the flow of matter the surface of the star. But even those mountains would be many smaller than a molehill, compressed by the immense gravity of the stars.

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