Astronomers have detected five more of the mysterious events known as fast radio bursts, one of them a never-seen-before double burst. Double bursts contradict many of the proposed explanations for these events, suggesting the source may be even more exotic than we thought. As co-finder Emily Petroff from Swinburne University tweeted: “We have no idea what's going on, but we know it's definitely something cool.”
Fast radio bursts (FRBs) were first discovered from records in 2007, and we finally saw one in real time last year. As their name suggests they are rapid bursts of radio energy, known to originate at great distances, and therefore contain a lot of energy. That aside, we don't know their source. Superficially similar bursts, dubbed perytons, turned out to be produced by microwave ovens being prematurely opened in telescope tea rooms.
Understandably, astronomers are keen to add to our limited data sample with just 11 recorded before this week, so the announcement in the Monthly Notices of the Royal Astronomical Society (pre-print on ArXiv) of five newly identified FRBs has generated plenty of excitement. The fact that one of these was a double event adds to the buzz.
The authors describe the double burst FRB 121002 as having a "clear two-component profile, each component is similar to the known population of single component FRBs and are separated by 2.4 milliseconds.” They added: “Many of the proposed models to explain FRBs use a single high energy event involving compact objects (such as neutron star mergers) and therefore cannot easily explain a two-component FRB.”
Coincidentally, FRB 121002's announcement comes just days after the publication of a paper that explained FRBs as the result of mergers between black holes and neutron stars. This work predicts a second FRB soon after the first. However, a co-author of the paper announcing the new discoveries, Dr. Ewan Barr of Swinburne University, told IFLScience this explanation should only account for one FRB in every thousand. If this is the only cause of double bursts, finding one in our first 16 seems unlikely.
All the FRBs identified in the paper occurred between 2009 and 2013 and were recorded during the Parkes High Time Resolution Universe high latitude survey and picked up in re-examination of archival data. The high latitude survey examined parts of the southern sky that tend to be neglected in projects exploring regions filled with objects from our own galaxy.
All show the characteristic FRB feature that lower frequencies arrive slightly after higher ones. Barr attributes this to impediment by low density free electrons in space. “The time between the arrival of different frequencies is dependent on how much material the pulse has passed through,” he told IFLScience.
FRB 121002 shows the largest delay yet recorded, indicating a tremendously distant origin, probably several billion light-years away. Besides the black hole-neutron star merger theory, other proposed explanations include evaporating black holes, supergiant pulsar pulses and the collapse of epically large stars, but these are hard to match with a double peak.