What are fast radio bursts?

What Are Fast Radio Bursts?

Not the Fast Radio Burst. Radio waves aren’t visible to the eye. This is something else, from the Hubble Space Telescope. See a spectrum of the burst below. Image via NASA/ ESA/ Hubble/ ScienceAlert.

Fast Radio Bursts (FRBs) are short, intense bursts of radio waves lasting perhaps a thousandth of a second, coming from all over the sky and of unknown origin.

 In a shock discovery that could help to solve one of astronomy’s greatest mysteries – on April 28, 2020 – astronomers used an Astronomer’s Telegram to announce a Fast Radio Burst originating from inside our Milky Way galaxy. That’s a first.

All other FRBs have been extragalactic, that is to say outside our galaxy. Even more importantly, the astronomers think they’ve also identified the source of the burst.

Explanations have ranged from neutron stars to supernovae to the inevitable aliens.

What Are Fast Radio Bursts?

Dynamic spectrum – a range frequencies over time – from the April 28, 2020, Fast Radio Burst, via Astronomer’s Telegram.

FRBs were first detected in 2007. This new detection of an FRB is, in astronomical terms, very close to home.

Astronomers found it using the CHIME (Canadian Hydrogen Intensity Mapping Experiment) radio telescope in Canada, an instrument designed specifically to study phenomena such as FRBs in order to answer major questions in astrophysics.

This particular telescope has greatly increased the bursts’ detection rate since its first light in September 2017.

This is the first fast radio burst known to have a steady beat

A periodic flurry of radio waves from some unknown object in
deep space could help astronomers figure out what’s triggering similar radio
bursts in other galaxies.

Since 2007, researchers have cataloged over 100 fast radio bursts, or FRBs, coming from
every direction in the sky. But it’s unknown what causes these radio bursts.
Only 10
have been seen to repeat (SN:
8/14/19), and none of those had exhibited any sort of steady tempo —
until now.

One of the known repeaters has a relatively brief window of activity
about every 16 days, researchers report January 28 at arXiv.org. That means
something about the source or its environment is reliably controlling the burst
activity, a potential clue to the true nature of these enigmatic objects.

Dongzi Li, an astrophysicist at the University of Toronto,
and colleagues found the pattern in data from the Canadian Hydrogen Intensity Mapping
Experiment, or CHIME, radio telescope in British Columbia. They determined
that the FRB blasts out about one to two radio bursts per hour for four days
and then goes silent for just over 12 days before usually repeating the cycle.

What Are Fast Radio Bursts?

“This is very significant,” says Duncan Lorimer, an
astrophysicist at West Virginia University in Morgantown and co-discoverer
of the first FRB (SN: 7/25/14). “It’s potentially going to take us
in an interesting direction to get to the bottom of these repeaters.”

One possible explanation for the periodicity is that the FRB
is orbiting something else, perhaps a star or black hole. In that case, the
16-day period might reveal how often the source of the radio waves is pointed
toward Earth.

Alternatively, stellar winds from a companion might
periodically boost or block the radio pulses. Winds might also explain why not
every 16-day cycle produces bursts: If the companion occasionally belches out
more material than usual, that could mask the FRB’s signal.

Either explanation implies that repeating FRBs — or at
least, this one — might come paired with something else.

Li and her colleagues aren’t ready to rule out stand-alone
objects, where the 16-day period might arise from the FRB rotating or wobbling.
But that scenario is a bit tougher to reconcile with the data.

For example, one
popular FRB culprit is a type of highly magnetic neutron star known as a
magnetar.

But known magnetars in our galaxy spin around once every 12 seconds
or less, the team notes, a far cry from the fortnight needed for this FRB.

This particular radio burst was also recently traced to a
star-forming region in a spiral galaxy nearly 500 million light-years away from
Earth (SN: 1/6/20). Future scans of its home with telescopes sensitive
to other electromagnetic radiation, such as X-rays or gamma rays, might whittle
down the list of suspects and move astronomers closer to solving this cosmic
mystery.

There’s also hope that this find is just the first of many periodic
FRBs to be detected. “There’s nothing particularly special about this
repeater,” Lorimer says. “The fact that they detected periodicity on this one
hints that other ones will have periodicity as well.”

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Astronomers Now Think They Can Explain Fast Radio Bursts

Between this past Christmas and New Year’s Day, Brian Metzger realized he had his home to himself — no emails coming in, no classes to teach — and maybe, just maybe, the glimmer of an answer to one of astronomy’s most stubborn mysteries.

He chased hard after the lead, worried a little error could unravel everything or that someone else would put together the same pieces first. “You’re racing a little bit against the clock, because other people probably see this as well,” said Metzger, an astrophysicist at Columbia University. “It can kind of become all-consuming.”

Along with scores of other researchers around the world, Metzger has spent the last few years brainstorming ways to understand fast radio bursts (FRBs).

These are millisecond-long blips of intense and unexplained radio signals that pop up all over the sky, temporarily outshining radio pulsars in our galaxy despite being perhaps a million times farther away. Before 2013, many astrophysicists doubted that they even existed.

In the years since, researchers have invented dozens of possible explanations for what might be causing them. One catalog counts 48 separate theories, a tally that until recently outnumbered the events themselves.

An FRB theory needs two parts, roughly akin to a suspect and a weapon in a cosmic game of Clue. The suspect is an astrophysical beast that can unleash vast sums of energy. The weapon is something that will transform that energy into a bright, head-scratchingly unusual radio signal.

Now Metzger and his colleagues think they have reconstructed the crime scene. Earlier this month they released a paper on the scientific preprint site arxiv.org that sketched out a way for FRBs to arise from explosions in regions of space cluttered with dense clouds of particles and magnetic fields.

Fast Radio Bursts (FRBs) – What Are FRBs? – Radio Bursts in Space

Jingchuan Yu, Beijing Planetarium

  • Astronomers have discovered a new type of fast radio burst (FRB).
  • FBR 121102 has a staggering 157-day cycle, according to researchers, who studied the cosmic event during a four-year observation period.
  • The team used the the Lovell Telescope at England's Jodrell Bank Observatory.

Fast radio bursts (FRB) are one of the most mysterious events in the cosmos.

These powerful bursts of energy have stumped astronomers since they first discovered them in 2007. Since then, researchers have spotted evidence of more than 100 FRBs. And now, an international study team team believes it's uncovered new information about a well-known FRB that could shed light on how they form.

Over the course of four years, the scientists used the 250-foot-wide Lovell Telescope at Jodrell Bank Observatory in England to study FRB 121102, a previously discovered repeating radio burst. They found that FRB 121102—one of two known repeating FRBs—seemed to have a peculiar cycle, flaring up after 90 days and then vanishing for 67 days.

The other repeating fast radio burst, FRB 180916.J10158+56, has a much shorter cycle at just 16 days. The scientists posted their observations June 7 in the journal Monthly Notices of the Royal Astronomical Society.

“The discovery that at least some Fast Radio Bursts (FRBs) repeat has ruled out cataclysmic events as the progenitors of these particular bursts,” the authors wrote in their paper, which can read on arXiv.

While some astronomers have suspected a type of spinning neutron star called a magnetar could cause cause FRBs, Others have suggested they may be the work of extraterrestrial civilizations trying to reach out. This latest research may have ruled out the magnetar theory.

“Detecting a periodicity provides an important constraint on the origin of the bursts and the activity cycles could argue against a precessing neutron star,” lead researcher Kaustubh Rajwade, of The University of Manchester, said in a press statement. The cyclical nature of these events suggests maybe they're linked to a binary system, where one object circles another, but more research is needed.

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‘Magnetic Star’ Radio Waves Could Solve the Mystery of Fast Radio Bursts

In recent weeks, astronomers have been monitoring strange, high-energy emissions from the corpse of a long-dead star some 30,000 light-years away.

Within the emissions, they found something surprising: a powerful blast of radio waves that lasted mere milliseconds.

The blast was, in fact, the brightest outburst ever seen from this star or any of its kind—immensely magnetic neutron stars known as magnetars.

The eruption of radio waves, though originating in our own galaxy, is remarkably similar to fast radio burst (FRBs)—fleeting, intensely bright radio flashes launched by as yet unidentified objects that, until now, had only been observed coming from other galaxies. Although it may raise just as many questions as it answers, this latest observation could solve at least one riddle surrounding the cosmic origin of FRBs.

“Without overusing the word ‘breakthrough,’ this is really a breakthrough,” says Jason Hessels of the Netherlands Institute for Radio Astronomy and the University of Amsterdam. “It doesn’t quite get you all the way there, but it gets you such a huge step of the way” toward cracking the case of FRBs.

At least two radio observatories spotted the recent radio burst in late April.

Teams traced the radio waves back to a highly magnetic neutron star—the remnant of a star that was maybe 40 or 50 times as massive as the sun—called SGR 1935+2154.

Located deep in the disk of the Milky Way, the dense, dead celestial body had been slinging high-energy radiation into the cosmos for a week or so, as a rare class of objects called soft gamma-ray repeaters are known to do.

It is the first time anyone has seen a blaze of radio waves alongside such a barrage of gamma rays. And because of the radio burst’s tremendous brightness and short duration, some astronomers now think it is a great local model for FRBs that come from billions of light-years away.

Even so, making that tenuous link more definitive requires a sober assessment of how this source is different from previously observed FRBs, says Emily Petroff of the University of Amsterdam.

“As always with FRBs, you have to make sure that you don’t miss the forest for the trees. We can get really hung up on one source being typical.

But we’ve already seen so many times—again and again over the past five years—that’s not always true.”

In Search of Explanations

FRBs have been among the universe’s most stubborn mysteries for more than a decade. Traveling at the speed of light, these radio blasts typically wash over Earth after traversing the cosmos for billions of years, suggesting that whatever celestial engine is heaving them into space must be extremely powerful.

All the bursts observed so far have come from distant galaxies. Over the years, astronomers have amassed dozens of hypothetical origins for the phenomenon.

Among them are evaporating black holes, explosively dying stars, massive colliding objects and—perhaps less seriously—the technobabble transmissions of smart, talkative aliens.

As the observations have piled up, the hypotheses have improved. Astronomers saw some bursts that repeated, proving that whatever their source was, producing a single FRB would not cause its self-destruction.

Teams started catching bursts in real time, pointing multiple telescopes to stare at spots on the sky where one originated. It was not long before several of them had been traced back to their host galaxy.

But even though astronomers had gathered data on hundreds of bursts by early 2020, their origins remained fundamentally clouded.

Astronomers closer to cracking mystery of fast radio bursts

The CHIME telescope in Canada searches the sky for highly energetic cosmic events called fast radio bursts.Credit: CHIME Collaboration

Astronomers are edging closer to discovering what causes brief, powerful flashes in the sky known as fast radio bursts (FRBs), after a Canadian telescope discovered eight more of the most intriguing type of these blasts — those that repeat their signals.

FRBs are intensely energetic events that flare for just milliseconds, seemingly all over the sky and from outside the galaxy. But their cause has remained a mystery since the first FRB was identified in 2007.

Astronomers hope that studying bursts that repeat their flashes, rather than just flare once, can help to elucidate the origins of FRBs.

That’s because it’s easier for high-resolution telescopes to make follow-up observations of ‘repeaters’ and trace their origins than of one-off blasts.

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Of the roughly 75 FRBs seen before this month’s discoveries, just 2 bursts were known to be repeaters. The first of these has been extensively studied, and the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope discovered the second repeater earlier this year.

CHIME’s latest results, published1 on the arXiv preprint server on 9 August, now show that repeaters are far from rare.

In the past few weeks, another telescope, the Australian Square Kilometre Array Pathfinder, also found a repeater, bringing the total so far to 11 — although researchers are yet to publish this result.

Even More Repeating Fast Radio Bursts Discovered

In September of 2017, the Canadian Hydrogen Intensity Mapping Experiment (CHIME) in British Columbia commenced operations, looking for signs of Fast Radio Bursts (FRBs) in our Universe.

These rare, brief, and energetic flashes from beyond our galaxy have been a mystery ever since the first was observed a little over a decade ago.

Of particular interest are the ones that have been found to repeat, which are even rarer.

Before CHIME began collecting light from the cosmos, astronomers knew of only thirty FRBs.

But thanks to CHIME’s sophisticated array of antennas and parabolic mirrors (which are especially sensitive to FRBs) that number has grown to close to 700 (which includes 20 repeaters).

According to a new study led by CHIME researchers, this robust number of detections allows for new insights into what causes them.

First detected in 2007, FRBs constitute one of the greatest mysteries facing astronomer today.

While this phenomenon is incredibly powerful, temporarily outshining even the brightest galactic pulsars by a factor of about one million, they are also incredibly short-lived (lasting about a millisecond).

Even though many have been localized to distant galaxies, astronomers are still not sure what accounts for them.

That is not to say there aren’t a whole lot of theories, which range from them being the result of rotating neutron stars or the collapse of strange star crusts to evidence of extra-terrestrial activity.

This latter theory is entertained in part because of the few cases where FRBs were found to repeat.

No known natural phenomena can account for this, hence the speculation that it could be a form of communication.

This is the question that an international team led by Emmanuel Fonseca – a postdoctoral researcher in the Department of Physics at McGill University, and part of the McGill Space Institute – sought to address. For the sake of their study, the team relied on data from 9 new repeating FRB sources that were recently detected by CHIME to see what they could infer.

Two Populations

Mysterious Pattern Of ‘Cosmic Radio Bursts’ From A Distant Galaxy Repeats Every 157 Days, Say Scientists

Artist's impression of an orbital modulation model where the FRB progenitor (blue) is in an orbit … [+] with a companion astrophysical object (pink). The type of companion star is not know but models exist which suggest that it could be anything from a black hole to a massive star.

Kristi Mickaliger

One of the great mysteries of modern astronomy has been revealed after a five years-long observation found a repeating pattern in a radio signal coming from a small dwarf galaxy about three billion light-years from Earth. 

It comes in the wake of another landmark study into fast radio bursts (FRBs), one of the hottest topics in astronomy. Very short, but bright radio pulses, FRBs were detected for the first time in 2007 by the Parkes radio telescope in Australia. 

These massively energetic flares of radiation in the radio spectrum last for just a few milliseconds. Mostly they happen once. 

Although several thousand FRBs are thought to be coming in from deep space every day, and from every direction, there are two that are particularly interesting—FRB 121102 and FRB 180916.J10158+56. 

These two keep repeating. 

First noticed in 2014 by the Arecibo radio telescope in Puerto Rico, FRB 121102 was detected again in 2016 to make it the only such signal that had occurred more than once.

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