What a nearby kilonova would look like

If two dense neutron stars collided relatively close to Earth, the resulting kilonova would shine day and night with the brightness of the moon squeezed into a small dot.

“At night, it would be by far the brightest thing up there,” says physicist Imre Bartos of the University of Florida in Gainesville, who describes what the bright burst would look like in a study posted May 7 at arXiv.org.

The first such burst of light and energetic particles seen in real time was spotted in 2017, after physicists detected gravitational waves from a neutron star crash (SN: 11/11/17, p. 6). That discovery, which occurred 130 million light-years away and was visible only with telescopes, proved that kilonovas sprinkle the universe with heavy elements like gold, silver, platinum and uranium.

While it’s unlikely a kilonova will happen nearby anytime soon, one occurred about 1,000 light-years from where Earth is now (although 80 million years before the solar system formed), Bartos and physicist Szabolcs Marka of Columbia University reported May 1 in Nature. That event seeded the solar system with elements that make up planets today.

 “We wanted to make this more visual, what this distance means,” Bartos says. So he and Nihar Gupte, also at the University of Florida, simulated the light spectrum emitted by the 2017 kilonova as it would appear if it were just 1,000 light-years away. It would start out bluish in color, but would turn red over a few days to a week as debris from the kilonova smothered bluer wavelengths of light (SN: 3/30/19, p. 7). After about a week, the kilonova would fade to nothing.

A kilonova could happen that close to Earth once every 100 million years, astrophysicists estimate. So we’re not likely to see one, but some may have occurred over Earth’s 4.5-billion-year history. That could have had painful consequences for anything alive on the planet at the time. If the kilonova released a gamma-ray burst, like the 2017 kilonova did, that torrent of high-energy particles of light could have indirectly wiped out life on Earth (SN: 1/10/15, p. 15).