The ravenous cosmic “Black Widow” is the heaviest known neutron star

The ravenous cosmic “Black Widow” is the heaviest known neutron star

By Will Dunham

WASHINGTON (Reuters) – Astronomers have observed the most massive known example of an object called a neutron star, one classified as a ‘black widow’, which became particularly powerful by engulfing most of the mass of a stellar companion caught in an unhappy cosmic marriage .

The researchers said the neutron star, spinning wildly at 707 times per second, has a mass about 2.35 times that of our Sun, perhaps the maximum for such objects before turning black hole would collapse.

A neutron star is the compact, collapsed core of a massive star that exploded as a supernova at the end of its life cycle. The star described by the researchers is a highly magnetized neutron star called a pulsar that emits beams of electromagnetic radiation from its poles. As it rotates, from the perspective of an observer on Earth, these rays appear to pulse – similar to the rotating light from a lighthouse.

Only one other neutron star is known to spin faster than this one.

“The heavier the neutron star, the denser the material at its core,” said Roger Romani, director of Stanford University’s Center for Space Science and Astrophysics and co-author of the research published this week in the Astrophysical Journal Letters.

“So, as the heaviest known neutron star, this object represents the densest matter in the observable universe. If it were heavier, it would collapse into a black hole, and then the stuff inside would be beyond the event horizon, sealed off forever from observation,” added Romani added.

A black hole’s event horizon is the point of no return, beyond which everything, including light, is irretrievably sucked in.

“Since we don’t yet know how matter works at these densities, the existence of this neutron star is an important probe of these physical extremes,” said Romani.

Located in our Milky Way toward the constellation of Sextans and officially named PSR J0952-0607, the neutron star is about 20,000 light-years from Earth, Romani said. A light year is the distance that light travels in one year, 5.9 trillion miles (9.5 trillion km). The researchers studied it with the Keck I telescope in Hawaii.

Stars about eight times the mass of the Sun convert hydrogen in their cores into heavier elements through thermonuclear fusion. Building up about 1.4 times the mass of our Sun in iron, that core collapses into a neutron star only about the size of a city in diameter, with the rest being blown away in the supernova explosion.

Its matter is so compact that the size of a sugar cube would outweigh Mount Everest.

This neutron star inhabits a so-called binary star system in an orbit with another star. The neutron star is a species dubbed the “black widow,” named after female black widow spiders that eat their male mates after mating.

It was apparently born with the usual mass of a neutron star, about 1.4 times that of our Sun, but its gravitational pull robbed material from its companion star and allowed it to grow to a mass that appears to be on the upper limit before the Physics would dictate a collapse into a black hole, the densest of all known objects.

Its companion star was almost denuded, losing perhaps 98% of its mass to the Black Widow, making it about 20 times the mass of our Solar System’s largest planet, Jupiter — a far cry from its original size.

“It has almost swallowed the mass of an entire sun without becoming a black hole again. So it should be close to the black hole collapse,” said Romani.

(Reporting by Will Dunham; Editing by Lisa Shumaker)

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