Scientists have observed gravitational waves emanating from the collision of two dense, dead stars.

Axar.az reports citing BBC.

It's the second time the international Ligo-Virgo collaboration of laser labs has picked up such a signal.

What makes this one different, though, is the combined mass of the two merging neutron stars - at three and a half times that of our Sun.

A coalescing system this big has never been seen in our galaxy and challenges researchers' expectations.

All the previously known so-called binary neutron stars detected by radio telescopes have been no larger than 2.7 times the mass of the Sun.

"So, if you're trying to explain how these systems are formed, you have to also explain why such a thing that we now know exists has never been seen in [our] galaxy. Or is there some reason radio surveys are blind to it?" said Katerina Chatziioannou from the Flatiron Institute, New York.

The union of the two neutron stars almost certainly produced a black hole.