The origin of powerful one-off flashes of energy from intergalactic space has puzzled astronomers for more than a decade.



Key points: One-off fast radio bursts (FRB) were first discovered in 2007, but we've never been able to pin down where they come from

One-off fast radio bursts (FRB) were first discovered in 2007, but we've never been able to pin down where they come from Astronomers used the Australian Square Kilometre Array Pathfinder telescope in Western Australia to pinpoint the location of a newly discovered FRB

Astronomers used the Australian Square Kilometre Array Pathfinder telescope in Western Australia to pinpoint the location of a newly discovered FRB Identifying where FRBs come from will help us work out what causes them, and allow us to probe intergalactic space

Now, for the first time, they've pinpointed the location of one of these bursts to a galaxy 3.6 billion light years away.

The burst, known as a fast radio burst or FRB, only lasted for 1.3 milliseconds but was so powerful that it emitted as much energy as the Sun would in 80 years.

The Australian-led research team were not only able to identify which galaxy the burst came from, but tracked the signal to its precise location 13,000 light years from the galaxy's centre, they report in the journal Science today.

That sort of precision is equivalent to standing on the Moon and looking down at the Earth, said lead author and astronomer Keith Bannister of the CSIRO.

"You know not only the city it came from, but also the suburb and even the city block," Dr Bannister said.

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FRBs were first discovered in 2007 using data from CSIRO's Parkes telescope, and are one of radio astronomy's biggest mysteries.

"We just don't understand what kind of object in the universe can make radio waves that only last for a millisecond and that are so bright, because we think they come from literally halfway across the universe," Dr Bannister said.

"The second reason that they're really interesting is that when an FRB goes off, as it travels towards the Earth it actually picks up lots of information about the gas that it's travelling through on its way."

And that gas between galaxies, also known as the intergalactic medium, is very difficult for us to see or measure in any other way.

Although astronomers predict that 2,000 FRBs happen across the sky every day, we'd only detected 85 of them until this latest discovery.

Most of those 85 have been one-off bursts, although two have sent out repeat bursts from the same patch of sky from time to time.

This has made it possible for astronomers to detect the location of one of these "repeaters", said study co-author and astronomer Adam Deller of Swinburne University.

"Once you know approximately where it is, you know where to look," Dr Deller said.

But, he said, tracking down the location of the one-off bursts has proven much more challenging.

"If you want to catch a one-off burst then you've really only got for as long as you can save the raw data, which in our case is a couple of seconds."

How they did it

Pointing ASKAP's antennas in the same direction enabled the astronomers to pinpoint the location of the fast radio burst. ( Supplied: CSIRO )

The team are no strangers to spotting fast radio bursts.

Last year, the team bagged a haul of 20 bursts using the Australian Square Kilometre Array Pathfinder (ASKAP) telescope.

The telescope, located 300 kilometres north-east of Geraldton at the Murchison Radio-astronomy Observatory in Western Australia, uses multiple dishes spread across a 6km area.

Previously, the astronomers pointed the dishes in different directions — known as fly-eye mode — to cover a large slab of sky.

But this time they pointed them all in the same direction.

As the signal travels through space it hits each of the dishes at a slightly different time, allowing the astronomers to calculate the location of its source.

"When [the dishes are] all working together you can figure out how the wave of radiation washed over all of the different telescopes and that tells you where it came from," Dr Deller said.

After they'd pinpointed the location of the burst, known as FRB 180924, colleagues at optical telescopes around the world snapped an image of the galaxy it came from, and measured how far away it was.

One of these galaxies is not like the other

The fast radio burst originated in the galactic suburbs of this host galaxy. ( Supplied: K Bannister et al 2019 )

But while they've identified the galaxy, the result has thrown up even more questions about what actually produces these strange signals.

The galaxy identified for this burst is very different from the host galaxy where the repeater burst known as FRB 121102 is located.

While the repeater comes from a dwarf galaxy that is vigorously forming new stars, the new burst comes from a galaxy that is a similar size to our Milky Way and is a lot more pedestrian.

"We now have to take a step back and say you don't have to be in an unusual galaxy to produce an fast radio burst," said astronomer Ryan Shannon from Swinburne University, a co-author on the paper.

"They're still very unusual, it's just that the environments that produce them don't have to be," Dr Shannon said.

Dr Bannister said the team hope to pinpoint more of these elusive bursts.

"The trick is to find as many of these as we can, and that gives us a statistical idea of how much gas there is in the universe, and that would be a really exciting thing to do," he said.

Locating the origin of a single burst was a big step forward in solving the mystery of what causes these bursts, said astrophysicist Tara Murphy of the University of Sydney, who was not involved in the study.

Professor Murphy said the discovery demonstrated the power of what new telescopes like ASKAP can do.

"This is something we've been hoping ASKAP will be able to do, and this is the first proof that it can do it," she said.

"We should be able to routinely start identifying where [FRBs] are from, and once we've got some sample of them where we know their host galaxy, we will be able to identify what causes them."