A highly energetic fast radio burst, which broke the distance record, provides a crucial test for theories of these events’ origins.
Astronomers have spotted the most distant fast radio burst ever recorded, its light having traveled 8 billion years to arrive at Earth. Finding more bursts like it could lead to a way of pinning down the missing mass thought to reside between galaxies.
As its name suggests, a fast radio burst (FRB) is a sudden and rapid release of radio waves. In less than a millisecond, such events can release the same amount of energy as the Sun does over decades. The exact trigger mechanism is unclear, but so far the sources of most FRBs have been fairly near to us in cosmic terms, their radiation traveling less than 5 billion years (for astronomers, closer than a redshift of 0.5). This newly discovered source, dubbed FRB 20220610A, went off at around redshift 1.
The team found the record-breaking FRB in June 2022 with the Australian Square Kilometre Array Pathfinder (ASKAP) facility. “Using ASKAP’s array of dishes, we were able to determine precisely where the burst came from,” says team lead Stuart Ryder (Macquarie University, Australia). “Then we used the . . . Very Large Telescope (VLT) in Chile to search for the source galaxy, finding it to be older and further away than any other FRB source found to date.” Their findings are published in Science (preprint available here).
Extreme distance wasn’t the only way that FRB 20220610A exceeded expectations. The burst energy was 3.5 times the maximum energy of previously discovered FRBs, challenging current theories of how these events are produced.
One of the most common explanations for FRBs is that they come from highly magnetized neutron stars called magnetars — either from their surfaces or where they interact with surrounding material. “We have detected an FRB-like signal from a magnetar in own galaxy,” says Daniele Michilli (MIT), who was not involved in the research. “However, the magnetar burst was 100 million times weaker than this new discovery, and it is very unclear whether magnetars can produce bursts covering this huge energy range.”
“Weighing” the Universe
Whatever their origin, FRBs can be used to gauge the amount of material that lies between us and the FRB. Free electrons between the FRB and Earth disperse the radio waves en route. From the 50 or so FRBs identified so far, astronomers have established the so-called Macquart relation. Named after the late Australian astronomer Jean-Pierre Macquart, it says that the further away a FRB is, the more the burst is dispersed and hence the more material there is.
That relation has been called into question lately, but this distant FRB puts it back on solid ground. “Some recent fast radio bursts appeared to break this relationship,” says Ryder. “Our measurements confirm the Macquart relation holds out to beyond half the known universe.”
“It is exciting to see that with FRBs like this we can probe these otherwise unseen regions of the universe,” says Ziggy Pleunis (University of Toronto), who was not involved in the research.
According to the team, what we’ve found so far is only the tip of the astronomical iceberg. The upcoming Square Kilometre Array Observatory and Extremely Large Telescope could help detect thousands of similarly distant FRBs and perhaps even some that break this new record. “We will be able to use [FRBs] to detect matter between galaxies, and better understand the structure of the Universe,” says team member Ryan Shannon (Swinburne University of Technology, Australia).
It’s important work. “We think that . . . matter is hiding in the space between galaxies, but it may just be so hot and diffuse that it's impossible to see using normal techniques,” Shannon says. “More than half of what should be there today is missing.” And distant FRBs could help us find it.