Key takeaways

  • Gravitational wave detectors, LIGO and Virgo, detected cosmic ripples indicating a distant event likely involving a black hole consuming a neutron star.
  • Neutron stars are dense remnants of supernovae, comparable in size to cities but with masses greater than our Sun.
  • This discovery, potentially confirming the existence of binary systems of black holes and neutron stars, opens new avenues for understanding celestial phenomena.
  • The absence of electromagnetic signals suggests the neutron star may have been consumed entirely by the black hole.
  • Confirmation of this event would mark a significant milestone, completing a trifecta of gravitational wave detections this decade, including neutron star mergers.

In the same decade that gravitational waves and a neutron star merger were discovered, scientists have now discovered what they believe to be the first observation of a black hole eating a neutron star.

Gravitational wave detectors in Italy and the United States, known as LIGO and Virgo, discovered unmistakable ripples in space and time related to an event that occurred 8,550 million trillion kilometers distant from Earth.

Astronomers are studying the detection data to determine the size of the two objects that collided to cause such dramatic waves, but the event is most likely a black hole swallowing a neutron star.

“About 900 million years ago, this black hole ate a very dense star, known as a neutron star, like Pac-man – possibly snuffing out the star instantly,” said Susan Scott, leader of the General Relativity Theory and Data Analysis Group at Australian National University and chief investigator with the ARC Centre of Excellence for Gravitational Wave Discovery. “The ANU SkyMapper Telescope responded to the detection alert and scanned the entire likely region of space where the event occurred, but we’ve not found any visual confirmation.”

Black holes and neutron stars are essentially the remains of stars that have died.

The tiniest stars in the universe are neutron stars, which are supernova leftovers. Their diameters are similar to that of cities like Chicago or Atlanta, yet they are very dense, having masses larger than our sun.

When enormous stars collapse at the end of their lifetimes, they create a region of accelerating gravity that nothing, even light, can escape.

This new finding, like the other major discoveries this decade, has the potential to reveal additional critical evidence for hitherto unknown phenomena in space.

“We have always thought that there should be binary systems of a black hole and a neutron star circling each other out in space, so if this event is confirmed, it would be the first evidence that such systems do actually exist, and that some of them are spiraling closer and closer and eventually smashing together,” Scott said.

If the neutron star has a similar mass as the black hole, astronomers predict more orbits to bring them closer together. Scott said that this would tear the neutron star, resulting in detectable electromagnetic radiation. The signal would inform scientists about the attributes of the star, hinting to its enigmatic composition.

However, if the masses of the two objects differ, the neutron star will most likely be eaten whole and not produce radiation. Because there was no signal in the region where the incident occurred, the researchers assume this is what happened.

Astronomers seek to know the masses of the two objects. A black hole is defined as an entity with a mass larger than five times that of the Sun. A neutron star is one that has a mass less than three times that of the Sun.

Scott suggested that the smaller object may be a very light black hole, which would be an amazing consolation prize.

“We are not aware of any black holes in the universe with masses less than about five solar masses,” he added. “This would raise many new questions such as, ‘how does such a light black hole form?'”

If the observation of the black hole consuming the neutron star is verified, the detectors will have completed their trifecta this decade, which includes gravitational waves and neutron star collisions.

Gravitational waves are ripples across space and time. Gravitational waves, as well as light and heavy materials such as gold, are released when neutron stars collide.

Scientists believe they may have detected the first-ever collision between a neutron star and a black hole, as well as a collision involving two neutron stars and three probable black hole mergers, after the gravitational wave detectors were turned on in April of this year. The detector observations are considered candidates until further data is available to confirm them.

If this trifecta is complete, the researchers hope to identify further systems, such as black holes and neutron stars merging.

“We can better estimate the population size of these systems in the universe and also better understand how these systems ‘get together’ in the first place,” Scott said. “On the extended wish list we would soon hope to have a supernova which goes off somewhere close so that we can capture the expected gravitational waves from this type of event and better model the supernova process.”

The detection teams are also working on a method to detect the collision of two neutron stars, which momentarily produces a larger neutron star. It is likely that this larger neutron star may be short-lived, but any discovery from it would help astronomers understand the collision mechanism for neutron stars and their structure.

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