“Something Unexpected Going On” –Astronomers Tune In to Fast Radio Bursts Cosmic Frequency

Fast Radio Bursts

 

Fast radio bursts (FRBs) are one of the great mysteries of the cosmos. They are brief, bright flashes of radio waves that last a few milliseconds. Although thousands occur over the entire sky every day – only a couple dozen have ever been seen. Their origins remain a mystery, but among the possibilities are cataclysmic events such as the evaporation of black holes and collisions between neutron stars.

New Tool Reveals the Structure of Matter in the Universe?

FTBs represent a new, very unusual, unexpected phenomenon. The bursts come from other galaxies, meaning incredible amounts of energy are required to produce them – some bursts contain more energy than our Sun produces in decades. Second, FRBs have the potential to be a new tool that we can use to understand the structure of matter in the universe.

Dispersion -Colors of Radio Light

The key property of the bursts that could turn them into a valuable tool is their dispersion: shorter (bluer) wavelength radio waves arrive at the telescope before the longer (redder) ones. The dispersion is due to the radio signal traveling through plasma (gas of charged particles). Since the dispersion grows with distance traveled in plasma, it is used to estimate the distance to the source of the radio signal. 

Two Australian radio telescopes synchronized to observe the same point of sky have discovered more about one of the Universe’s most mysterious events in the research. The Curtin University-led Murchison Widefield Array (MWA) and the Commonwealth Scientific and Industrial Research Organization (CSIRO) Australian Square Kilometer Array (SKA) Pathfinder (ASKAP) telescopes were searching the sky for fast radio bursts, which are exceptionally bright flashes of energy coming from deep space.

Conflicting Signals

In research published in the Astrophysical Journal Letters, astronomers describe how ASKAP detected several extremely bright fast radio bursts, but the MWA–which scans the sky at lower frequencies–did not see anything, even though it was pointed at the same area of sky at the same time.

Lead author Dr Marcin Sokolowski, from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR), said the fact that the fast radio bursts were not observed at lower frequencies was highly significant.

“When ASKAP sees these extremely bright events and the MWA doesn’t, that tells us something really unexpected is going on; either fast radio burst sources don’t emit at low frequencies, or the signals are blocked on their way to Earth,” Sokolowski said.

Study co-author Dr Ramesh Bhat, who is also based at ICRAR-Curtin, said it required considerable co-ordination to get the CSIRO-led ASKAP telescope and Curtin-led MWA telescope pointed at the same area of sky at the same time.

Fast Radio Bursts –“A New Enigmatic Pattern Discovered”

‘Technological Tango’

Both telescopes were able to capture the same view because the two telescopes are located side-by-side in the desert of Western Australia’s remote Murchison region.

“Fast radio bursts are unpredictable, so to catch them when both telescopes are looking in the same direction isn’t easy,” Dr Bhat said. “It took many months of ASKAP and the MWA co-tracking the same area of sky, ensuring the best overlap of their views possible, to give us the chance at catching some of these enigmatic bursts. The challenge was in making it all happen automatically, but it really paid off.”

In an email to The Daily Galaxy Dr. Bhat wrote: “Basically, our wisdom tends to improve rapidly in this fast-evolving field, and that is precisely what has happened over the past few years. We now know that the FRB emission is not necessarily persistent across the large frequency range of the electromagnetic spectrum; instead, it tends to be modulated, oftentimes with a speckle type structure across frequency. We have seen it for many cases.

“When ASKAP sees these extremely bright events and the MWA doesn’t, that tells us something really intriguing about the nature of their emission; in fact, the past few years of investigation reveal it is often modulated in frequency and tends to show large speckles. Uncovering this may help us understand the environments of these enigmatic bursts.”

ICRAR-Curtin astronomer Dr Jean-Pierre Macquart, a co-author of the research who died in 2020, said fast radio bursts have perplexed astronomers ever since the first burst was discovered in 2007. “It’s really thrilling to have a clue about the origins of these incredible bursts of energy from outside our galaxy.”

“The MWA adds an important piece of the puzzle,” Macquart noted, “and it was only made possible with this ‘technological tango’ between the two telescopes. It’s an exciting development because it unites the two teams and it brings home the advantage of having the two telescopes at the same site.”

“Cosmic Broadcasts” –Energy Bursts from the Most Powerful Magnetic Fields in the Universe

The Last Word –”Probably are not extraterrestrials saying hello.”

A 2020 research paper has provided new clues that galactic magnetars –young pulsars that spin more slowly than ordinary pulsars and have the most powerful magnetic fields in the universe– lying in close proximity to a black hole, could perhaps be the source of “fast radio millisecond-long bursts,” or FRBs –high-energy blasts that originate beyond our galaxy but whose exact nature and origin is unknown.

“More than 60 of these surprise broadcasts have been recorded so far,” reports Dennis Overbye for the New York Times. “About the only thing astronomers agree on is that these signals probably are not extraterrestrials saying hello.”

Avi Shporer, Research Scientist, with the MIT Kavli Institute for Astrophysics and Space Research via Dr. Ramesh Bhat, International Centre for Radio Astronomy Research (ICRAR) and The Conversation

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