Scientists have picked up more mysterious repeating radio signals from deep space - including one from a nearby galaxy.
Fast radio bursts (FRBs) are intensely bright millisecond-long bursts of radio waves coming from beyond our galaxy. They are some of the most enigmatic and powerful events in the universe.
Many theories have been put forward about what could be causing them - including the suggestion that - but none of them is a perfect fit.
What makes it even more difficult is that there seem to be two types of FRBs - bursts that happen just once, and bursts that repeat many times from the same spot in space.
Up until now, scientists had only detected only two so-called repeaters, but the Canadian Hydrogen Intensity Mapping Experiment (CHIME) has found eight more.
Repeaters are much easier to study than bursts that only occur once, because they can be monitored over long periods of time, allowing scientists to observe any changes.
The first repeater that was discovered - known as FRB 121102 - was also the first FRB to be tracked back to its home galaxy 3 billion light-years away.
However, at least one of the new repeaters, which CHIME saw repeating ten times over the course of four months, appears to be a lot closer.
This could be particularly useful as astronomers try to unravel the mystery of what is causing them.
"You want to be able to characterise the galaxy and pinpoint exactly where in the galaxy these bursts are coming from, and that's impossible if the galaxy is halfway across the universe," Gregg Hallinan at the California Institute of Technology told New Scientist .
"It's way easier if it's right in our backyard."
Last month, astronomers succeeded in tracing a back to a Milky Way-sized galaxy 7.9 billion light-years away.
The discovery suggests that a leading theory for what causes FRBs - the eruption of plasma from young, highly magnetic neutron stars, or "magnetars" - may need to be rethought.
