by Sebastian Anthony
July 29, 2014

from ExtremeTech Website








Since 2001, the Parkes radio telescope in Australia has been picking up mysterious, unidentified bursts of energy that astronomers have since dubbed "fast radio bursts" (FRB).


At first, because no other telescope in the world had ever seen these bursts, it was assumed that these FRBs were probably just glitches in the telescope's electronics - but now, 13 years later, a telescope on the other side of the planet in Puerto Rico has detected an FRB.


This second FRB detection means that it isn't just a fluke - and more importantly, that astronomers have absolutely no idea what's causing them.


Some theories have suggested that FRBs originate from an evaporating black hole, or perhaps solar flares from nearby stars, or - and this is coming from one of the astronomers who first recorded the FRBs - they could even be "signatures from extraterrestrial civilizations."


The first FRB was discovered by chance in 2007, when a team of astrophysicists led by Duncan Lorimer was poring through old archival data from the Parkes Observatory in New South Wales, Australia (pictured top).


On the night of August 24, 2001, a five-millisecond burst of radio waves erupted from an otherwise calm patch of night sky near the Small Magellanic Cloud and hit the telescope.


Lorimer and co analyzed the single burst for years, but without any additional data from further bursts it was impossible to say if it was actually a new astrophysical phenomenon - or just a man-made or local source of interference, such as an electronics glitch or lightning storm.


Finally, in 2013, another team finally got the go-ahead to analyze a full year's worth of data from the Parkes telescope - and sure enough, they found four more similar bursts (A Population of Fast Radio Bursts at Cosmological Distances).



The Arecibo observatory in Puerto Rico.



Up until this point, though, all of these readings were from the same telescope - and, as any scientist will tell you, it's unwise to draw any conclusions from just a single patient or case study.


Now, however, the Arecibo radio telescope in Puerto Rico - almost 10,000 miles away from Parkes - has detected a fast radio burst as well. Now, some 13 years after it was first detected, and seven years of random-anomaly purgatory, astronomers are taking the FRB very seriously indeed.


As for what causes FRBs, no one knows - and that's why the astronomical community is so darn excited.


The 2013 Parkes study, which found four bursts while looking at a tiny patch of sky for a year, suggests that FRBs are actually quite common, perhaps occurring as regularly as once every 10 seconds.


FRBs are also intensely bright. Such regularity and intensity probably rules out a few likely origins, such as the evaporation of black holes or the merger of neutron star pairs. Gamma ray bursts have the right kind of intensity, but they only happen once a day or so.


One possible explanation is that FRBs are created by magnetars - not fantastical monsters that you might face in a game of Dungeons & Dragons, but rather special neutron stars that can flare up and release as much energy in a millisecond as our Sun releases in 300,000 years.



The Parkes radio telescope in Australia

[Image credit: Ian Sutton]



Or, of course, the other possibility is that FRBs are produced by some kind of intergalactic extraterrestrial civilization.


Speaking to NPR, Duncan Lorimer says with a little bit of chagrin that,

"there's even been discussions [about FRBs] in [research papers] about signatures from extraterrestrial civilizations."

Lorimer is referring to a single research paper that explores the possibility of the bursts being intentionally created by an alien civilization to broadcast their existence to the rest of the universe.


This is just a theory, of course, but really, we know so little about FRBs that just about any theory is worth investigating at this point.


The next step is to perform real-time triangulation of FRBs to get a better idea of which galaxy they're originating from. Data from radio telescopes across the world will be analyzed to look for more FRBs, and in the future some telescopes will be specifically tasked with discovering and classifying FRBs.


Lorimer, speaking to Scientific American, says,

"It's not very often in astronomy that you get completely new classes of objects coming along, especially ones as strange as these. We are witnessing the birth of an entirely new area of research."















A Brilliant Flash, Then Nothing

-   New "Fast Radio Bursts" Mystify Astronomers   -
by Lee Billings

July 9, 2013

from ScientificAmerican Website



Ultrafast, ultra-bright radio pulses

from sources unknown

could help map intergalactic matter,

but only if astronomers

can figure out their origin



CSIRO/Harvard/Swinburne Astronomy Productions




Every now and then things go "bump!" in the cosmic night, releasing torrents of energy that astronomers can't easily explain.


Not that they mind: most times an energetic riddle flares up in their view of the sky, major epoch-setting discoveries are sure to follow. This was the pattern for pulsars - rapidly spinning city-size stellar remnants that steadily chirp in radio.


It was also the pattern for gamma-ray bursts - extreme explosions at the outskirts of the observable universe thought to be caused by stellar mergers and collapsing massive stars.


Now the pattern is playing out again, with last week's announcement that an international team of researchers has detected brief, bright bursts of radio waves washing over Earth from mysterious sources that may be billions of light-years away.


The findings, reported in the July 5 Science (A Population of Fast Radio Bursts at Cosmological Distances), could open an entirely new window on the universe by allowing scientists to measure the composition and dynamics of the intergalactic medium - the cold, diffuse plasma that lies between galaxies.


Using a year's worth of data gathered from some 10 percent of the sky by the 64-meter Parkes radio telescope in Australia, the team detected four bursts from far outside the galactic plane, each occurring only once and lasting a few thousandths of a second.


According to Dan Thornton, a PhD candidate at the University of Manchester in England who led the study, the results suggest that these "fast radio bursts," or FRBs, probably occur as often as every 10 seconds or so, nearly 10,000 times a day.

"If we had radio telescopes watching the entire sky, that's how many we think we'd see each day," Thornton says. "We haven't seen more of these until now only because we've been looking at small regions of the sky for small amounts of time."


"The discovery of fast radio bursts at the Parkes Observatory, if confirmed at other observatories, would be a monumental discovery, comparable to that of cosmological gamma-ray bursts and even pulsars," says Shrinivas Kulkarni, a Caltech astrophysicist who was not involved with the recent study.


"Great discoveries need the greatest proof, however, and I eagerly look forward to confirmation of these events at other radio bands and other observatories."




One flash, followed by years of uncertainty


In 2007 a different team discovered the first FRB entirely by chance while analyzing archival data from the Parkes telescope.


The astronomers' interest was piqued by an event from the night of August 24, 2001, when a five-millisecond burst whispered into the telescope from a seemingly blank region of sky near the Small Magellanic Cloud, a dwarf galaxy thought to orbit our Milky Way.


Examining the data in more detail, the team's leader, West Virginia University astrophysicist Duncan Lorimer, found something curious in the dispersion of the burst's wavelengths.


Its short-wavelength components had arrived at the telescope a fraction of a second before longer wavelengths, an effect that can be caused by longer-wavelength light moving ever so slightly slower through electrons in clouds of cold plasma that suffuse the space between stars and galaxies.


The longer the delay between the arrival of a burst's short and long wavelengths, the more intervening electrons it had passed through and the greater the distance it traveled. Lorimer and his colleagues were shocked by the results of their calculations, which suggested the burst had come from as much as a few billion light-years away.


Lorimer looked for the burst's repetition in some 90 hours of additional Parkes observations but came up empty.


Because of the burst's extreme brightness, short duration and singular occurrence, Lorimer suspected it might represent an entirely new, previously undetected astronomical radio source that astronomers might somehow use as a plumb line to investigate the ionized contents of the intergalactic medium.


Year after year his team's proposals to search for more such bursts were rejected, and separate searches found only one tentative candidate.


Other astronomers began suggesting the "Lorimer burst" might have been only some errant terrestrial signal caused by man-made interference or natural sources such as lightning.


Perhaps it had all been too good to be true.

"That kept us awake at night," Lorimer recalls. "We wondered whether what we had seen was just a fluke, an artifact."

The four new FRBs gathered by Thornton's team at Parkes have eliminated most lingering doubts.


The burst with the smallest wavelength dispersion seems to have reached us after passing through some 5.5 billion light-years of space; the burst with the largest dispersion appears to be from nearly twice as far out, originating some 10.4 billion light-years away.


One of the four bursts also bears the likely imprint of turbulence in the intergalactic medium, a subtle stretching out of its pulse shape probably caused by electron scattering.


Making those same measurements for further FRBs would give astronomers the unprecedented ability to estimate the strength of intergalactic magnetic fields.





From sources unknown


Even though their extragalactic origins are largely confirmed, the FRBs' sources remain unknown.


In follow-up multiwavelength observations, no trace of an FRB precursor or afterglow has been found, and because of the relatively low angular resolution of most current radio telescopes, astronomers have not been able to pinpoint any galaxy as a site for any FRB's source.


Based on each burst's brevity, brightness and far-distant origin, whatever generated them gave off a truly enormous amount of energy in radio waves, all from an emission region no bigger than a few hundred kilometers.


And yet, according to Thornton's colleague Matthew Bailes, an astronomy professor at Swinburne University of Technology in Melbourne, Australia, the signal from a mobile phone broadcasting from the surface of Earth's moon would be brighter than a typical FRB by a factor of 1,000.


Such apparent faintness, Thornton says, means that,

"it would take Parkes operating full-time for a million years to collect enough FRBs to equal the kinetic energy found in a single flying mosquito."

The high occurrence rate of FRBs paired with their immense intrinsic luminosity has, however, largely ruled out a handful of hypothesized sources.


The FRBs are too bright to be radio-wave burps of evaporating supermassive black holes at galactic centers, and they are far too frequent to be easily explained as the echoes from energetic mergers of neutron star pairs.


Similarly, gamma-ray bursts occur only about once a day, not often enough to be obviously associated with FRBs.


One new hypothesis, espoused by Heino Falcke of Radboud University Nijmegen in the Netherlands and Luciano Rezzolla of the Max Planck Institute for Gravitational Physics in Potsdam, posits that FRBs are the farewell messages of dying stars dubbed "blitzars," putative rapidly spinning "supramassive" neutron stars that would otherwise become black holes.


As a blitzar loses energy and spins down over time, it suddenly crosses a threshold where it can no longer support its weight, and as it collapses an FRB is emitted.

"When the black hole forms, the magnetic fields will be cut off from the star and snap like rubber bands," Falcke explained in a press release.


"As we show, this can indeed produce the observed giant radio flashes. All other signals you normally would expect - gamma rays, x-rays - simply disappear behind the event horizon of the black hole."

Bailes finds the blitzar explanation difficult to swallow; reconciling it with the estimated FRB occurrence rate would require the majority of neutron stars to be in this unlikely supramassive state.



"the problem with many of these more exotic scenarios is they aren't easily falsifiable," he says. "We wouldn't be able to detect anything else from these things after they're locked away behind a black hole's event horizon."

Bailes's preferred FRB source is something called a magnetar, rare neutron stars with the most powerful magnetic fields ever measured.


In the so-called 'Christmas event of 2004', Bailes notes, astronomers observed a magnetar flare up on the far side of the Milky Way in a "giant burst" (below video):







In a millisecond the magnetar erupted with a bit more energy than the sun releases in 300,000 years.


Astronomers believe the burst was caused by a starquake, a sudden rearrangement of the magnetar's structure to release built-up stresses associated with its whirling magnetic field.

"Even a tiny fraction of that energy converted to radio waves would give the kind of luminosity we need to satisfy an FRB's energetics, and the millisecond timescale is perfect for our duration," he says.




A 3-D map of matter


Although researchers may argue about an FRB's source, there is universal agreement about the mysterious bursts' applications.

"If we can trace an FRB to a specific galaxy, we can then independently measure the distance to that galaxy," Thornton says. "Comparing the FRB's dispersion measure with that galactic distance would yield the average electron density between Earth and that other galaxy."

And because all those electrons come from baryons - subatomic particles such as protons and neutrons - they would be a proxy measurement of the amount and distribution of unseen ordinary matter that exists between and even within far-distant galaxies.

"If we find many different FRB host galaxies at many different distances," Thornton says, "we can begin to create a 3-D map of intergalactic baryonic matter and magnetic fields."

Tracing FRBs to their galaxies would require their real-time detection by a radio telescope such as Parkes, rapidly followed by more detailed observations using high-resolution radio facilities such as the Jansky Very Large Array in New Mexico.


A new real-time detection scheme has just come online at Parkes, Bailes says, and the telescope has already observed more FRBs.


For Lorimer, the new discoveries are a vindication.

"I feel relieved," he says.


"It's been a long time coming. FRBs are really going to drive demand for the next generation of radio telescopes as we try to figure out what's making things go off all across the universe like this every 10 seconds.


For a while there will be more theories than individual detected bursts, but soon we'll have hundreds of these things from across the entire sky.


It's not very often in astronomy that you get completely new classes of objects coming along, especially ones as strange as these.


We are witnessing the birth of an entirely new area of research."