Ominous signals have been detected from deep space. Photo / News.com.au
By Jamie Seidel for news.com.au
The number of alien, repeating radio blasts astronomers have detected in deep space has just tripled.
What are they? Where do they come from? What do they mean?
Fast radio bursts (FRBs) were first discovered by Australia's Parkes telescope in 2007. They immediately became one of the strangest mysteries of the known universe.
About 100 have been found since.
They are fleeting — but incredibly powerful — signals seemingly originating out of nowhere. And they appear to be travelling almost unbelievably vast distances.
But some are posing a new quandary: 15 bursts have been discovered to repeat.
And that doesn't seem normal.
Therefore aliens?
It's one possibility some are considering.
But Curtin University investigator Dr Jean-Pierre Macquart told news.com.au: "I wouldn't be calling Agent Mulder just yet."
A fast radio burst represents an event of incredible power.
"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," says 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."
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.
"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.
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)?
There are 48 different theories circulating in astronomy circles.
"The number of contenders appears limited only by our imagination," Dr Macquart says.
But there are boundaries to that imagination.
Something has to be causing the accumulation and release of the tremendous energies required to propel such a signal billions of light-years across space and time. Added to the mix must be something that is focusing the energy into narrow bands of the radio spectrum.
They could be merging neutron stars or neutron stars crashing into black holes. Or not.
"One of the most obvious ways to do this is to store the energy in an extremely strong magnetic field, such as that which might occur in a magnetar," Dr Macquart says. "But there are surely other contenders that we haven't thought of yet."
"Over the last few years, and particularly the last few months, we have rapidly transcended the age of supposition and speculation to one of hard data and compelling evidence," Dr Macquart says.
Most importantly, astronomers have begun to trace FRBs back to their source.
"The key impediment to understanding their origin has been our ability to pinpoint the locations of these bursts with sufficient accuracy to be able to state where these things are going off definitively."
And one early, highly contentious, piece of conjecture appears to be true: They were originating at distances measured in the billions of light-years.
"The burst properties, if inferred to be at these distances, were so outrageous that people thought there had to be a mistake," he says.
"We know now it was no mistake".
And that has some serious implications for astrophysics.
Astronomers are beginning to doubt the accuracy of what has until recently been regarded as one of the fundamentals of astronomy: the Hubble Law. It puts a fixed number on the expansion rate of the observed universe.
But the math isn't adding up.
Now, FRBs may offer the means to reveal whether or not the universe is tearing itself apart.
"When you have such impulsive signals, you can make measurements that people only dreamed about," Dr Macquart says.
"For me, though, the real lure of FRBs is in using their dispersive properties — the fact that lower frequencies of the pulse arrive delayed due to their propagation through matter — to weigh the universe. This will reveal the location of the missing matter that we think is lurking out in the vast voids of space the lie in-between galaxies."
Since the FRB's discovery, several projects around the world have geared up to examine these mysterious signals. Australia remains at the forefront with the Commensal Real-time ASKAP Fast Transients survey project.
Also sniffing the skies for radio bursts are the Very Large Array in New Mexico and the DSA-10 project run by the California Institute of Technology.
Dr Macquart says we should expect to find a whole lot more bursts as the search gathers momentum.
"Our estimates suggest that several thousand of these bursts go off across the sky each day. But most radio telescopes only see a tiny fraction of the sky at once."
It's also a process that devours valuable computation time: Every pixel recorded every millisecond must be monitored to see if an event has gone off.
New phased array feed technology is allowing the ASKAP facility to scan a 30-degree square of the sky (an area about 100 times bigger than the moon).
"But the raw data rate out of a telescope like that is 10 trillion measurements per second or about 75 terabits per second," he says.
Buried amid the torrent of binary data, somewhere, will be the answer.
And it's not likely to be what we expect.
"The universe has always proven itself to be more imaginative than we are," Dr Macquart says.
Jamie Seidel is a freelance writer. Continue the conversation @JamieSeidel
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