WASHINGTON—Astronomers have observed the most massive known example of an object called neutron starone classified as a “black widow” made particularly strong by gobbling up most of the bulk of a fellow star trapped in an unhappy cosmic marriage.
The researchers said the neutron star, which spins wildly at 707 times per second, has a mass about 2.35 times that of our sun, putting it perhaps at the maximum possible mass for such objects before they collapse. to form a black hole.
A neutron star is the collapsed compact core of a massive star that exploded as a supernova at the end of its life cycle. The one described by the researchers is a type of highly magnetized neutron star called a pulsar that releases beams of electromagnetic radiation from its poles. As it rotates, these rays appear to pulsate from the perspective of an observer on Earth, similar to the spinning light of a lighthouse.
Only one other neutron star is known to rotate faster than this one.
“The heavier the neutron star, the denser the material at its core,” said Roger Romani, director of the Center for Space Sciences and Astrophysics at Stanford University and co-author of the research published this week in the Astrophysical Journal Letters.
“So, as the heaviest known neutron star, this object features the densest material in the observable universe. If it were heavier, it should collapse and become a black hole, and then the material inside would be behind the event horizon, forever cut off from any observation,” added Romani.
The event horizon of a black hole is the point of no return beyond which everything, including light, is irretrievably absorbed.
“Since we don’t yet know how matter works at these densities, the existence of this neutron star is important evidence of these physical extremes,” Romani said.
The neutron star, which resides in our Milky Way galaxy in the direction of the constellation Sextans and formally named PSR J0952-0607, is about 20,000 light-years from Earth, Romani said. A light year is the distance that light travels in one year, 5.9 billion miles (9.5 billion kilometers). The researchers studied it using the Keck I telescope in Hawaii.
Stars that are about eight or more times the mass of the sun transform hydrogen into heavier elements through thermonuclear fusion in their cores. When they pack about 1.4 times the mass of our sun in iron, that core collapses into a neutron star only the size of a city in diameter, with the rest vanishing in the supernova explosion.
This neutron star inhabits what is called a binary system, in orbit with another star. The neutron star is a so-called “black widow” species, named after the female black widow spiders that eat their male partners after mating.
It was apparently born with the usual mass for a neutron star, about 1.4 times that of our sun, but its gravitational pull pulled material from its companion star, allowing it to grow to an apparently upper limit mass before it physics would dictate a collapse. in a black hole, the densest of all known objects.
Its companion star has been stripped bare, losing perhaps 98 percent of its mass to the black widow, leaving it with about 20 times the mass of our solar system’s largest planet, Jupiter, a far cry from its original size.
“In a case of cosmic ingratitude, the black widow pulsar, which has devoured a large part of its companion, now heats and evaporates the companion to planetary masses and perhaps complete annihilation,” added study co-author Alex Filippenko, from the University of California, Berkeley, astronomy professor.
By Will Dunham
To follow