Astronomers announced today that they have detected a spark that was produced when two neutron stars collided. The spark plus the gravitational waves produced by the collision are evidence of a massive explosion. The gravitational wave evidence of such collisions (possibly by black holes colliding) has been observed before, but the event detected on August 17th of this year was the first time such an event was accompanied by a flash, which indicates it was caused by neutron stars instead of black holes. The event is called GW170817 after the date, but is described as "a Rosetta stone for astronomy."
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.
The resulting explosion is called a "kilonova," which is 1,000 times brighter than a supernova. Physicists believe such collisions are what produced some of the heavier elements of the universe, like gold. Read more about the kilonova at the Atlantic.
You can watch a video about the discovery here.