The heaviest neutron star formed after it swallowed a companion star

The dense, collapsed remnants of a massive star, called a neutron star, weigh more than twice the mass of our Sun, making it the heaviest neutron star known to date. The object rotates 707 times per second, which also makes it one of the fastest rotating neutron stars in the Milky Way.

The neutron star is known as the black widow because, like these arachnids female spiders, which after mating consume much smaller male partners, the star crushed and ate almost the entire mass of its companion star.

This stellar celebration allowed the black widow to become the heaviest neutron star observed so far.

Astronomers were able to weigh the star PSR J0952-0607 using using the sensitive Keck Telescope at the WM Keck Observatory on Maunakea, Hawaii.

The observatory’s low-resolution spectrometer detected visible light from a shattered companion star that was glowing due to high temperatures.

The companion star is now the size of a large gaseous planet, or 20 times the mass of Jupiter. The side of the companion star facing the neutron star is heated to 10,700 degrees Fahrenheit (5,927 degrees Celsius) — hot and bright enough to be seen with a telescope.

The cores of neutron stars are the densest matter in the universe, with the exception of black holes, and 1 cubic inch (16.4 cubic centimeters) of a neutron star weighs more than 10 billion tons, according to study author Roger W. Romani, professor of physics at Stanford University in California.

According to the researchers, this particular neutron star is the densest object within sight of Earth.

Astronomers observed a dim star (green circle) that had almost completely lost its mass due to an invisible neutron star.  A striped star is much fainter and smaller than a regular star (top).

“We know approximately how matter behaves at nuclear densities, for example, in the nucleus of a uranium atom,” said Alexei Filippenko, co-author of the study. Filippenko holds the double title of professor of astronomy and eminent professor physical sciences at the University of California at Berkeley.

“A neutron star is like one giant nucleus, but when you have one and a half solar masses of this matter, which is about 500,000 Earth masses of nuclei tied together, it is completely unclear how they will behave.”

A neutron star such as PSR J0952-0607 is called a pulsar because as it rotates, the object acts like a cosmic beacon, regularly emitting light via radio waves, X-rays, or gamma rays.

Astronomers have discovered gravitational waves caused by the collision of massive neutron stars

Ordinary pulsars spin and flash about once per second, but this one pulses hundreds of times per second. This is because the neutron star becomes more energetic as it rips material away from the companion star.

“In the case of cosmic ingratitude, the black widow pulsar, which absorbed most of its partner, is now heating and vaporizing the satellite to planetary masses and possibly to complete destruction,” Filippenko said.

Astronomers first discovered neutron star in 2017, and Filippenko and Romani have been studying similar black widow systems for more than a decade. They were trying to figure out how big neutron stars could get. If neutron stars become too heavy, they collapse and become black holes.

According to the researchers, the star PSR J0952-0607 is 2.35 times the mass of the Sun, which is currently considered the upper limit for a neutron star.

“We can keep looking for black widows and similar neutron stars that roll even closer to the edge of a black hole. But if we don’t find them, that would strengthen the argument that 2.3 solar masses is the true limit beyond which they become black holes. “, – said Filippenko.

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