How small is the neutron star? The sphere 22 km in diameter weighs twice the mass of the sun

According to a new study, most neutron stars are equivalent to cramming twice the mass of the sun into a sphere 22 kilometers in diameter, a volume that means that black holes can usually directly devour the entire neutron star. Neutron stars are the remaining bodies of large-mass stars when they become supernovae, and their density is so large that a tablespoon of neutron star mass is placed on the Earth’s surface, equivalent to the weight of Mount Everest, compared with just 5 pounds of sun mass.

How small is the neutron star? The sphere 22 km in diameter weighs twice the mass of the sun

Most neutron stars are equivalent to cramming twice the mass of the sun into a sphere 22 kilometers in diameter, a volume that means that black holes can usually directly devour the entire neutron star.

Although neutron stars have maintained a range of mass for many years, it is still difficult to determine their diameter accurately. Most astronomers believe that the mass of neutron stars is compressed into a city-sized sphere.

Now, a new study that combines gravitational wave measurements with other techniques to produce the most accurate analysis of the size of neutron stars to date shows that a “standard” neutron star is about 22 kilometers in diameter and has an important impact when it approaches another of the universe’s most mysterious objects, the black hole. The latest measurements suggest that a black hole can normally swallow the entire neutron star, but astronomers can hardly find evidence using conventional telescopes.

How neutron stars are formed

When a large-mass star’s nuclear fusion, exhausting gas explodes, and when stellar material erupts violently in all directions, the remaining stellar material condenses into neutron stars, and if a star is large enough, its residual mass will further condense into a black hole.

Planetary systems built by independent stars like the sun are among the few in the universe, and most stars are in a multi-star planetary system, and when two large-mass stars evolve, their planetary systems will eventually exist in the form of two neutron stars, two black holes, or both. In recent years, astronomers have begun to study multi-star systems that throw gravitational waves when they spiral into the gravitational range of another star, a method that astronomers have recently made extremely accurate measurements of the size of neutron stars.

In 2017, the U.S. Laser Interference Gravitational Wave Observatory (LIGO) and the Italian Chamber of Women’s Detector received a gravitational wave signal indicating that two neutron stars collided about 120 million light-years from Earth. Soon after, traditional observatories began observing electromagnetic wave collisions, and these findings provided unprecedented insight into the mass and rotation of neutron stars.

Neutron Star Size

The Einstein Institute of Study in Germany combined these observations with models of subatomic particles operating under extremely high densities within neutron stars, and while it is impossible to reproduce such conditions in the Earth’s laboratory, physicists have shown that they can use existing theories to infer their calculations at the smallest scales. The case of distant neutron stars is inferred.

Their findings suggest that neutron stars should be between 21 and 24 kilometers in diameter, while a “standard” neutron star should be 22 kilometers in diameter, and that the latest measurements are twice as accurate as previous estimates of neutron star size.

Study author Collin Capano, a researcher at the Einstein Institute, said in a press release that neutron stars contain the densest cosmic material in the observable universe, and that they are in fact so dense that one can think of an entire neutron star as an atomic nucleus. It is about 22 kilometers in diameter, equivalent to the diameter of a city. By measuring the properties of neutron stars, we can master the basic physics principles that govern matter at the subatomic level.

swallowed by a black hole

Neutron stars are so small in diameter that if they are too close to the black hole, they may even be completely swallowed up by the black hole when they are running together. Astronomers have been keeping a close eye on the collision between black holes and neutron stars, which they expect will release intense electromagnetic radiation that land-based telescopes can observe directly.

However, if a neutron star is not crushed by a black hole when it collides with a black hole, land-based telescopes will not be able to detect any light, and gravitational wave detectors may not be able to distinguish between black hole merges and hybrids.

“We have now confirmed that in all cases, neutron stars will not be torn apart by a black hole, but will be completely swallowed up, and only when the black hole is very small or spins quickly can it destroy it before it devours it,” Kapano said. Only in this way can we see things other than gravitational waves. “

Astronomers don’t need long to verify that this view is correct, and gravitational wave detectors will become more powerful in the coming years, and if there are fewer collisions between neutron stars and black holes than expected, at least scientists will know why.

The new study is published in the March 9 issue of Nature Astronomy.