They came from outer space.
More “fast radio bursts" — very short-lived pulses of radio waves that come from across the universe — have been detected by astronomers using two of the world’s largest telescopes.
The bursts, which come from a galaxy over 3 billion light-years from Earth, repeated 16 times. So far, these are the only known fast radio bursts that have repeated.
Fast radio bursts, which are highly energetic but last just a few thousandths of a second, have puzzled astrophysicists since their discovery just over a decade ago. Since 2007, several of these bursts have been recorded by telescopes around the world.
What's also new about this discovery is that astronomers are starting to hone in on the specific source of the strange calls from across the universe.
The new findings suggest the bursts come from an environment with an extremely high magnetic field and temperature, and previously such conditions have been observed only in the vicinity of massive black holes.
The findings were presented Wednesday at the American Astronomical Society's annual meeting and published in the peer-reviewed British journal Nature.
The study authors say the source of the radio bursts is in an astonishingly extreme and unusual environment: likely from a highly magnetized rotating neutron star — known as a magnetar — that's located near a massive black hole that's still growing as gas and dust fall into it.
The short bursts range from 30 microseconds to 9 milliseconds in duration (a microsecond is one-millionth of a second). This indicates that the source could be as small as 6 miles across, which is the typical size of a neutron star.
"At this point, we don't really know the mechanism (of the bursts)," said study co-author Vishal Gajjar, a postdoctoral fellow at the University of California-Berkeley. "There are many questions, such as, how can a rotating neutron star produce the high amount of energy typical of a fast radio burst?"
Another possibility, though remote, is that the fast radio burst is a high-powered signal from an advanced civilization.
"We cannot rule out completely the extraterrestrial hypothesis for the fast radio bursts in general," Gajjar said.