15Sep2019

Mysterious Space Radio Bursts Continue To Baffle Astronomers

Since 2007, mysterious signals have been reaching Earth from other galaxies — now they’ve tripled frequency, and some of them are repeating the same message.  A fast radio burst represents an event of incredible power.

Fast radio bursts (FRBs) were first discovered by Australia’s Parkes telescope in 2007.

“The energy that some of these bursts release in about a millisecond is more than the entire amount of energy our sun puts out in over 10 years.” This comes from Dr Macquart of Australia’s International Centre for Radio Astronomy Research (ICRAR) facility in WA. “And this estimate is based just on the narrow range of radio wavelengths over which we detect them, so it is actually a lower limit to the amount of energy they liberate.”

Most have been seen in the UHF radio band. Some were detected at up to 8GHz. “They are not too dissimilar from the frequency bands at which some radars work,” Dr Macquart says. But we’re the ones doing the searching.

The first repeating FRB was traced to a point in the sky in 2017. Then, earlier this year, the Australian Square Kilometre Array Pathfinder (ASKAP) was able to pinpoint a non-repeating FRB. It was from a massive galaxy some four billion light-years away.

“Better yet, the precision of the radio position was so good we were able to say exactly where in the galaxy it occurred,” Dr Macquart says. It came from the outskirts of the galaxy, some 13,000 light-years from its centre.“This instantly invalidated a number of theories that supposed the bursts to be located with the processes that only occur right at the centres of galaxies, such as processes tied to supermassive black holes.”

The first repeating FRB was traced to a point in the sky in 2017.

The first repeating FRB was traced to a point in the sky in 2017.Source:Supplied

But attempts to correlate the position of FRBs by other means is proving problematic. “We have, of course, looked for optical emission soon after an FRB has gone off, but nothing has been found,” Dr Macquart says. And while embryonic gravitational-wave detection technology is promising, no conclusive links have yet been found.

So, are fast radio bursts and repeating FRBs the same phenomenon? The Parkes radio telescope and the massive 110m Greenbank Telescope in West Virginia have been monitoring the locations of previously detected FRBs to see if they, too, eventually repeat. One of them just has.

“The jury is still out on whether repeating FRBs come from the same types of objects that the apparently non-repeating FRBs do,” Dr Macquart says.

HERE BE ALIENS?

“We haven’t identified a possible natural source for (FRBs) with any confidence,” says Avi Loeb of the Havard Smithsonian Centre for Astrophysics. “An artificial origin is worth contemplating and checking. He postulates a solar-power array twice the size of the Earth could generate enough energy to create a focused radio transmission capable of traversing billions of light-years.

But why build such a device? The energy within such a transmission could be used to propel a light-sailed vessel weighing almost a million tonnes through space. “That’s big enough to carry living passengers across interstellar or even intergalactic distances,” added co-author Manasvi Lingam. And the reason why we see such a brief flash, they argue, is the brief time the narrow beam aligns with Earth.

No conclusive links have yet been found between fast radio bursts and repeating FRBs.

No conclusive links have yet been found between fast radio bursts and repeating FRBs.Source:Supplied

Dr Macquart, however, isn’t convinced: “So many of the properties of these signals just don’t add up as artificially produced signals.” Are they instead pulsars (a rapidly rotating neutron star that emits a beam of radio waves)? Are they magnetars (neutron stars with immensely strong magnetic fields)?

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