Just what the heck are fast radio bursts?
Let me be clear right off the bat: No one knows. But we just got a step closer to understanding them, which infuriatingly, also means things are even more complicated than they were before.
Fast radio bursts, or FRBs, are one of the more enduring cosmological mysteries today. They are as advertised: Very fast (usually a few milliseconds at most) and very powerful flashes of radio emission from the sky. Lots of things out there can emit radio waves: Planets (Jupiter is a big source), the Sun, stars, exploding stars, galaxies, dust, you-name-it. But these tend to emit radio waves persistently. Even things known to flash in radio waves (like pulsars, which are rotating neutron stars) flash over and over again with a pretty well understood periodicity.
FRBs aren't like that. The first ones found were one-and-done, flashing once very briefly and then disappearing. That's irritating, because it's hard to learn anything about them. Then some were discovered to repeat, flashing multiple times, though without any sort of obvious period (in other words flashing at what seem like random intervals). That's interesting, because that means whatever causes repeating bursts isn't getting destroyed ...