Distant fast radio burst offers path to weigh the universe

An international team of scientists has discovered the most ancient and distant blast of cosmic radio waves (fast radio burst, or FRB) to date, located in a galaxy so far away that its light took eight billion years to reach Earth. The burst, named FRB 20220610A, was detected in June last year by CSIRO’s ASKAP radio telescope in Western Australia and smashed the research team’s previous distance record by 50%.

It is also one of the most energetic FRBs ever observed; in a tiny fraction of a second it released the equivalent of our Sun’s total emission over 30 years. The discovery has been described in the journal Science.

“Using ASKAP’s array of dishes, we were able to determine where the burst came from,” said Macquarie University’s Dr Stuart Ryder, who co-led the research team. “Then we used the European Southern Observatory’s (ESO) Very Large Telescope in Chile to search for the source galaxy. We found it to be older and further away than any other FRB source found to date.”

The researchers say the source of the burst was a group of two or three galaxies that are merging, supporting current theories on the cause of FRBs. As noted by study co-author Professor Elaine Sadler, from the Sydney Institute for Astronomy at the University of Sydney, “The distant galaxy where this burst originated looked quite different from the other galaxies where FRBs had been detected and we think we may be seeing the collision and merger of two galaxies rather than just a single galaxy.

“Galaxy collisions of this kind were more common in the distant and early universe than they are today. Even though this galaxy is billions of light years away, measurements with a range of telescopes have allowed us to measure its size and mass as well as the typical age and chemical composition of its constituent stars.

“This information is helpful in trying to pin down the physical mechanism that produces such highly energetic magnetic flares, represented by the FRBs.”

The discovery has also reaffirmed the concept that FRBs can be used to measure the ‘missing’ matter between galaxies, providing a way to ‘weigh’ the universe. Current methods of estimating the mass of the universe are giving conflicting answers and challenging the standard model of cosmology.

“If we count up the amount of normal matter in the universe — the atoms that we are all made of — we find that more than half of what should be there today is missing,” said Swinburne University of Technology’s Associate Professor Ryan Shannon, research team co-leader. “We think that the missing 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.

“Fast radio bursts allow us to detect this ionised material. Even in space that is nearly perfectly empty they can ‘see’ all the electrons, and that allows us to measure how much stuff is between the galaxies.”

Finding distant FRBs is key to accurately measuring the universe’s missing matter, as first demonstrated by the late Australian astronomer Jean-Pierre (J-P) Macquart in 2020. Ryder explained, “J-P showed that the further away a fast radio burst is, the more diffuse gas it reveals between the galaxies. This is now known as the Macquart relation. Some recent fast radio bursts appeared to break this relationship. Our measurements confirm the Macquart relation holds out to beyond half the known universe.”

About 50 FRBs have been pinpointed to date — nearly half using ASKAP — with the authors suggesting that we should be able to detect thousands of them across the sky, and at even greater distances. Shannon noted, “While we still don’t know what causes these massive bursts of energy, the paper confirms that fast radio bursts are common events in the cosmos and that we will be able to use them to detect matter between galaxies, and better understand the structure of the universe.”

ASKAP is currently the best radio telescope to detect and locate FRBs, but the SKA Observatory is currently building two radio telescopes in South Africa and Australia that will be capable of finding thousands of FRBs — including very distant ones that cannot be detected with current facilities. ESO’s Extremely Large Telescope, a 39-metre telescope under construction in the Chilean Atacama Desert, will be one of the few telescopes able to study the source galaxies of bursts even further away than FRB 20220610A.

Image caption: This artist’s impression (not to scale) illustrates the path of the fast radio burst FRB 20220610A, from the distant galaxy where it originated all the way to Earth, in one of the Milky Way’s spiral arms. Image credit: ESO/M Kornmesser.