Black holes detected swallowing neutron stars, just ‘like Pac-Man’

30 Jun 2021

Image: © K.Miłkowski/

Scientists have published the first evidence of this ‘remarkable’ event after detecting it twice in the space of 10 days.

For the first time ever, scientists have detected the collision of a black hole and a neutron star.

The never-before-observed event was documented not once, but twice, in the span of 10 days in January 2020, and the findings have been published in a new study in The Astrophysical Journal Letters.

The Laser Interferometer Gravitational-Wave Observatory (LIGO) in the US and the Virgo gravitational-wave observatory in Italy captured gravitational waves resulting from a merger of a neutron star with a black hole in two separate instances.

The LIGO system consists of two 4km, highly-sensitive laser beams that can detect even the faintest gravitational waves by monitoring the smallest stretching or squeezing of space time between two points of each laser.

More than 1,000 scientists worked on the international collaboration.

Susan Scott of the Australian National University, who was a co-author on the study, said that while the events occurred about a billion years ago, their meeting was so massive that we are still able to observe the gravitational waves today.

“Each collision isn’t just the coming together of two massive and dense objects. It’s really like Pac-Man, with a black hole swallowing its companion neutron star whole.”

“These are remarkable events and we have waited a very long time to witness them. So it’s incredible to finally capture them.”

To give a sense of scale for these events, one of the black holes had a mass nine times bigger than our sun and engulfed a neutron star that was twice our sun’s mass.

The smaller of the two collisions consisted of a black hole with about six times the mass of our sun and a neutron star with 1.5 times its mass.

This isn’t the first time that celestial giants have collided. Previous observations include the meeting of two black holes, as well as two neutron stars, but this is the first time a black hole has been observed colliding with a neutron star.

An image of two neutron stars colliding. They resemble orange spheres, with their edges blurring in the middle as they collide.

An image of two neutron stars colliding. Image: NASA

Gravitational waves are distortions in space time that were predicted by Albert Einstein’s theory of general relativity.

The first observation of gravitational waves was monumental for space fans when they were noted in 2015. While Einstein described these waves in the early 20th century, astronomers have spent decades searching for them.

Dr Johannes Eichholz, from the ANU Centre for Gravitational Astrophysics and an associate investigator with OzGrav, said detections like these collisions are “incredibly rare” but are important for scientific study.

“Like the ripples from these two events, which have been felt a billion years later, these findings will have a profound impact on our understanding of the universe for many years to come.”

Sam Cox was a journalist at Silicon Republic covering sci-tech news