Professor Susan Scott from the ANU Research School of Physics said last Wednesday, gravitational-wave discovery machines in the United States and Italy picked up ripples in space and time, believed to be from a black hole engulfing a neutron star around 8550 million trillion kilometres away from Earth.

Professor Scott said it appears the black hole "ate" the neutron star "like Pac-man" - devouring it in one, quick gulp.

If the star was slowly shredded, light or radio waves would have been detected, she said.

"This is the first time we've ever seen the capture of a neutron star by a black hole so this is a very big deal for us," Professor Scott said.

"We always believed it could happen and we expected that it would happen out there in the universe but this is the first time that it's ever been seen."

Both neutron stars and black holes are the super-dense remains of dead stars, which form when the star runs out of fuel and begins to collapse on itself.

It is thought only larger stars end up as black holes, because a black hole less than five times the mass of our Sun and a neutron star larger than 2.5 times our solar mass has never been detected.

But there was an "intriguing" and "remote" possibility that the object that was swallowed was also a black hole, meaning astronomers may have just found the lightest black hole ever, Professor Scott said.

"That would be a game changer for black holes," she said.

"That would be a really big thing if that were the case because we have no evidence of these very light black holes up to this point."

Scientists are still analysing the data to determine the exact size of the two objects, with the final results to be published in scientific journals.

The cosmic event was detected with the same instruments that uncovered the existence of gravitational waves in 2015. Until then, the tiny ripples in the curvature of space-time was the last outstanding prediction made in Einstein's 1915 theory of general relativity.