In September of 2015, astronomers detected, for the first time, gravitational waves, cosmic ripples that distort the very fabric of space and time. They came from a violent merger of two black holes somewhere in the universe, more than a billion light-years away from Earth. Astronomers observed the phenomenon again in December, and then again in November 2016, and then again in August of this year. The discoveries confirmed a century-old prediction by Albert Einstein, earned a Nobel prize, and ushered in a new field of astronomy.
But while astronomers could observe the effects of the waves in the sensitive instruments built to detect them, they couldn’t see the source. Black holes, as their name suggests, don’t emit any light. To directly observe the origin of gravitational waves, astronomers needed a different kind of collision to send the ripples Earth’s way. This summer, they finally got it.
Scientists announced Monday they have observed gravitational waves for the fifth time—and they’ve seen the light from the cosmic crash that produced them. The waves came from the collision of two neutron stars in a galaxy called NGC 4993, located about 130 million light-years from Earth.
Neutron stars are strange, mysterious objects, the collapsed cores of stars that exploded in spectacular fashion—supernovae—and died. These stars measure about the size of a metropolitan city, but have about the same mass as our sun. Astronomers had long predicted that when two neutron stars collide, the resulting explosion would produce electromagnetic radiation, in the form of optical light. The afterglow would shine bright enough to be seen through powerful telescopes, the first visible proof of a source of gravitational waves, provided the latter could also be detected.