Astronomers find source of four radio bursts

Fast radio bursts are one of the biggest mysteries in astronomy. The immensely powerful bursts of radiation appear randomly from points in the Universe. They flash without warning, releasing as much energy in the blink of an eye as our Sun will emit in 80 years.

They can’t be predicted, and usually occur only once, making them incredibly difficult to trace.

There have been a few successes – last year an Australian team traced a fast radio burst (FRB) back to its source galaxy. And now the same CSIRO team have traced three more FRBs back to their source, allowing researchers to look around their neighbourhood to try to understand what might cause them.

The results of these four FRB investigations have been published in the Astrophysical Journal Letters.

Finding the source is key to finding out what causes the bursts

The FRBs were detected and traced by the ASKAP telescope, which stands on Wajarri Yamaji land in outback Western Australia. Using a specially designed detector installed on the telescope, the researchers traced four one-off FRB’s back to their source – FRB 180924 (the burst reported last year), FRB 181112, FRB 190102 and FRB 190608.

Tracing them back to their source is a key step in finding out what causes the mysterious bursts. For the last decade-and-a-bit since they were discovered, they have remained a complete unknown.

“Just like doing video calls with colleagues shows you their homes and gives you a bit of an insight into their lives, looking into the host galaxies of fast radio bursts gives us insights to their origins,” says Dr Shivani Bhandari, who led the research at CSIRO.

Many ideas as to the source have been considered, ranging from supermassive black holes, to neutron stars, and even aliens (it’s not aliens, it’s never aliens).

But Bhandari says her results can trim down the likely sources.

“These precisely localised fast radio bursts came from the outskirts of their home galaxies, removing the possibility that they have anything to do with supermassive black holes,” says Bhandari.

Scientists traced the bursts back to massive galaxies – not dwarf galaxies

The researchers combined the ASKAP results with observations from some of the largest optical telescopes in the world to identify and investigate the galaxies the FRBs were emitted from. These included the Keck telescopes in Hawaii, Gemini South, ESO’s Very Large Telescope, Magellan Baade, and LCOGT-1m.

They found all four bursts came from massive galaxies that are forming new stars at a modest rate, very similar to our own Milky Way galaxy.

And that came as somewhat of a surprise – previous research traced repeating FRB’s to dwarf galaxies with very high star formation rates.

These galaxies also rule out some other sources of the bursts, says the CSIRO’s Professor Elaine Sadler, who also contributed to the research. These fast radio bursts could not have come from a super-luminous stellar explosion, or from cosmic strings, she says.

“Models such as mergers of compact objects like white dwarfs or neutron stars, or flares from magnetars created by such mergers, are still looking good.”

While scientists still aren’t sure what causes FRBs, ruling out some possibilities while seemingly supporting others is a vital step along the way to finding an answer. But for the moment, some of the most mysterious signals in the universe remain exactly that.

“Positioning the sources of fast radio bursts is a huge technical achievement, and moves the field on enormously,” says Dame Jocelyn Bell Burnell, who discovered pulsars as a postgraduate student in 1967. Dame Jocelyn was not involved in the current study.

“We may not yet be clear exactly what is going on, but now, at last, options are being ruled out.”

This article was first published on Australia’s Science Channel, the original news platform of The Royal Institution of Australia.