A black hole consumes a neutron star, creating ripples in space and time

TL;DR

Astronomers detected gravitational waves from an event 900 million years ago where a black hole consumed a neutron star, marking the first possible detection of this type. The event, observed by LIGO and Virgo, could provide insights into the behavior of binary systems involving black holes and neutron stars. Researchers believe the black hole swallowed the neutron star whole without emitting radiation. The detection, if confirmed, would complete a decade of major cosmic discoveries, from gravitational waves to neutron star mergers.

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Gravitational wave detectors in Italy and the U.S., known as LIGO and Virgo, picked up distinct ripples in space-time from an event that occurred 8,550 million trillion kilometers from Earth.

Researchers are now analyzing the data to determine the sizes of the two objects involved, but the event is likely a black hole consuming a neutron star.

“About 900 million years ago, this black hole consumed a very dense star, known as a neutron star, like Pac-Man – possibly snuffing out the star instantly,” explained Susan Scott, head of the General Relativity Theory and Data Analysis Group at Australian National University, and lead investigator at the ARC Centre of Excellence for Gravitational Wave Discovery. “The ANU SkyMapper Telescope reacted to the detection alert, scanning the entire region where the event may have happened, but we haven’t seen any visual confirmation.”

Essentially, black holes and neutron stars are remnants left behind after stars die.

Neutron stars are the smallest yet incredibly dense objects in the universe, left over after supernova explosions. Though their size is comparable to cities like Chicago or Atlanta, they have masses greater than our Sun.

When massive stars collapse at the end of their life cycle, they create a region of accelerating gravity so intense that not even light can escape, forming a black hole.

Like previous significant discoveries this decade, this detection could offer key evidence for unseen phenomena in space.

“We’ve long thought that black holes and neutron stars might exist as binary systems orbiting each other in space. If this event is confirmed, it will be the first evidence that such systems exist and are spiraling toward collision,” Scott said.

If the neutron star’s mass is not much smaller than the black hole’s, astronomers would expect more orbits before they merge, shredding the neutron star and emitting detectable electromagnetic signals, providing insights into its properties. However, if their masses are significantly different, the neutron star would likely be swallowed whole without emitting radiation. Since no signal was found in the region, researchers think this might be what happened.

Astronomers are eager to learn the masses of the objects involved. An object over five times the Sun’s mass is typically classified as a black hole, while anything under three solar masses is considered a neutron star.

There is a slight chance that the smaller object could be an unusually light black hole, which would still be a notable find, according to Scott.

“We don’t know of any black holes with less than five solar masses,” she said. “If one exists, it would raise new questions, like, ‘how does such a small black hole form?’”

If this detection of a black hole consuming a neutron star is confirmed, it would complete the major discoveries of the decade, including gravitational waves and neutron star collisions.

Gravitational waves are disturbances in space-time, and neutron star collisions produce gravitational waves, light, and heavy elements like gold.

Earlier this year, after the gravitational wave detectors were reactivated, scientists believe they may have detected several exciting events: the collision of a neutron star with a black hole, a neutron star merger, and three possible black hole mergers. These observations remain candidates until further confirmation.

If this trifecta is confirmed, researchers aim to find more systems involving black holes and neutron stars merging.

“This would help us better estimate how common these systems are and understand how they come together,” Scott added. “On our wish list is also the hope of witnessing a nearby supernova, so we can capture the gravitational waves it produces and improve our models of the supernova process.”

The detection teams are also working on finding signals from the brief creation of a larger neutron star formed by two colliding neutron stars. Though short-lived, any detection could provide new insights into the collision process and the structure of neutron stars.