New research suggests the origins of one of astrophysics' greatest mysteries.
Arecibo Observatory. Image: BrianPIrwin/Shutterstock
An international team of astrophysicists has traced the origin of the only known repeating fast radio burst, according to a study published this week in Nature. The phenomenon, characterized by intense millisecond-long blasts of radio energy, is among the most mysterious in astrophysics and has led even relatively serious people to start thinking in terms of aliens.
An analysis of 16 bursts detected with the William E Gordon Telescope at the Arecibo Observatory suggests that their origin is likely to be within a dwarf galaxy hosting a supermassive black hole (10 to 100 million times the size of our Sun) and a neutron star (a form of dead star) in its orbit. The key feature of such a neutron star would be its very high magnetic field, a sort of highly-energized cosmic afterlife. Such a field would serve to supply the massive amounts of energy packed into a fast-radio burst viewable here on earth.
Fast radio bursts (FRBs) are not uncommon. We see them all over the sky all the time. A FRB is simply a pulse of radio energy that lasts for just a few milliseconds, but what makes them especially weird and vexing is that they usually don't repeat. It's not like looking at, say, a pulsar, which emits radiation at regular, dependable intervals. If a pulsar is a lighthouse, then an FRB is a signal flare, albeit one that doesn't flare for long enough to reveal its source or much of anything.
What the researchers behind the current paper are after is the exception to this: a repeating FRB. The only one. While these signal flares are exploding in random places in the sky all the time, there's just this one out there that happens in the same place again and again. FRB 121102 is special: a mystery within an already mysterious phenomenon.
What gives the source conditions of FRB 121102 away is the bursts' polarization. Polarization is a kinda hard to think about property of light. Basically, imagine a wave moving in one direction, but that's also been rotated around an axis that's perpendicular to that direction of travel. Twisted light. In fact, the degree of twisting seen is here is among the most extreme ever seen from an astrophysical source.
The radio waves of FRB 121102 have been twisted, we think, because they passed through a strong magnetic field—possibly a ripping torrent of high-speed, highly-magnetized plasma. Based on this, we can guess that the FRB 121102 source is itself within such a field.
"We found something that is clearly in an extreme place and the extreme location may create a phenomenon that is one of the biggest astrophysical mysteries of recent times," offered study co-author Victoria Kaspi, a professor at McGill University and leading voice on pulsars and neutron stars, in a statement. "If you have an extreme object in an extreme environment, is that just a coincidence? FRBs have these huge explosions in radio waves and we don't know why that occurs. Maybe this is a clue to the mechanism that produces these explosions."
So, no, we don't really understand that mechanism yet. We just know that whatever it is, it's probably occurring within a cloud of highly-magnetized plasma. The good news is that FRB 121102 is apparently still at it and its future behavior will go a long way toward understanding its ultimate source, perhaps a magnetar in one of several possible configurations with a nearby black hole. In any case, when the Canadian CHIME Telescope (above) goes online later this year we'll have a way to look even deeper at FRB 121102's ultimate origin.