Mysterious radio signals originating from a body some 3 billion light-years away carry hints of an environment capable of producing extremely powerful magnetic fields — such as an undiscovered supermassive black hole or the remains of a supernova.
First discovered in 2007, fast radio bursts still continue to puzzle astronomers. These signals are aptly named, lasting up to a few milliseconds at best. Incredibly short-lived — but extremely energetic as well — during their fleeing lifetimes, these signals burn with a vengeance on instruments that can pick them up.
Such levels of energy betray the signals’ source as a very powerful body or event — however, it’s not a source that we have yet determined. Mostly, it comes down to their unpredictable nature, which has thrown a bag full of wrenches into attempts to properly understand these events. Here is where FRB 121102, sitting about 3 billion light-years away in a dwarf galaxy, comes into the picture.
Bursts for days
What’s so special about this body is that it fires such radio bursts repeatedly. Because it emits fast radio bursts in clusters, it’s possible to train more instruments on the source and gather data in real time. Sensing that answers lurk close, a team of astronomers decided to study the signals beamed from FRB 121102 and get to the bottom of things — but their results have merely deepened the mystery.
According to their observations, the signals from FRB 121102 appear to be “twisted” in a way indicative of an extreme stellar environment, the team reports, one that can spawn an extremely powerful magnetic field.
The researchers used the Arecibo (radio) Observatory in Puerto Rico and the Green Bank Telescope in West Virginia to look at FRB as it was emitting a burst. The plan was to measure the signal’s polarization (geometric orientation), a quality that can be influenced by local phenomena. Polarization was seen before in other fast radio bursts, but the values the team picked up were totally off the scale — some 500 times greater extreme than any other recorded burst.
The findings muddy our understanding of FRB 121102 even more. The working hypothesis up to now was that the source was a kind of neutron star: either a pulsar (which spins very fast) or a magnetar (which spins but also has an extra strong magnetic field). Because it’s found in a star-forming region of its host galaxy, it was believed that FRB 121102 was somehow linked to stellar birth or death. The new data, however, points to several new explanations.
“We’ve seen this effect in other fast radio burst sources before, but in this case the effect is 500 times larger than what we’ve seen at other sources,” said senior author Jason Hessels. “That was quite surprising.”
FRB 121102 may be a pulsar in close proximity to a growing supermassive black hole, the team reports. Plasma spinning around the black hole could lense and twist the light from FRB 121102 — but we have no way of explaining why a giant black hole would form in a dwarf galaxy — although, to be fair, we’ve seen supermassive black holes doing all kinds of strange things. Another possibility is that FRB 121102 is cloaked within a dense nebula, whose that affects the signal on its way to us. However, this hypothesis fails to explain how the signal remains as bright as what we’re picking up.
It’s also been suggested that the source is some kind of pulsar, however, that doesn’t fit with the incoming burst pattern. FRB 121102 doesn’t emit at regular intervals, as one would expect from a spinning neutron star and their highly regular periods, but in clusters of signals.
Whatever the case may be, we’re currently baffled by what we’re seeing. The team will continue to study FRB 121102 and fast radio bursts in general, but so far, only a few dozen individual sources have been found. Researchers, however, estimate that as many as 10,000 fast radio bursts flash across the night sky every single day — it’s just a matter of catching them.
The paper “An extreme magneto-ionic environment associated with the fast radio burst source FRB 121102” has been published in the journal Nature.