Somewhere out there in the darkest depths of our universe, something is generating mysterious eruptions of energy that are being detected as fast radio bursts - otherwise known as FRBs.
Since these weird phenomena were first discovered nearly a decade ago, astronomers have been at a loss to explain what they could be. Everything from the exotic (aliens?!) to the "mundane" (supernovas, boo) have been cited as possible culprits. Now, by painstakingly analyzing the signal of one of these pulses, astronomers may be on the trail to finally working out what the heck is rumbling the cosmos.
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FRBs last only a fraction of a second but pack a hell of an energetic punch. Because they are so transient, however, they're not easy to record. They flash, and they're gone. Also, as they have often traveled vast distances, their signals are stretched and blurred out. According to a Carnegie Mellon University press release, though only a few have been detected, astronomers think the universe sees tens of thousands of these pulses every single day, but to see one you need to be looking at the right place at the right time.
After analyzing hundreds of hours of data from the National Science Foundation's (NSF) Green Bank Telescope (GBT) in West Virginia, researchers stumbled across the most detailed signature of a FRB recorded to date. From this signal, they were able to gain a measure on its magnetic "fingerprint" to reveal the environment it must have been spawned.
"We now know that the energy from this FRB passed through a dense, magnetized region shortly after it formed," said astronomer Kiyoshi Masui, of the University of British Columbia and the Canadian Institute for Advanced Research. "This significantly narrows down the source's environment and type of event that triggered the burst."
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What's dense and extremely magnetized? Supernovas and star forming regions. But exactly where did this FRB originate? So far, the detected FRBs have originated in random parts of the sky; there appears to be no pattern, and this particular FRB was no different. But the one thing that set this event apart - dubbed "FRB 110523″ - is the detail held in its signal. Now the detective work could begin.
Finding FRB 110523 was no easy task; the researchers had to scan through 40 terabytes of radio data looking for the split-second pulses. They found 6,000 candidate FRBs in the data, but the vast majority were of too low a quality for analysis or confirmation. Another problem is that, after travelling potentially billions of light-years to reach Earth, these pulses become smeared or blurred, an effect known as "dispersion delay." This has the effect of blending FRBs into the radio data, hiding it from view. The researchers therefore had to create a computer algorithm to track down these smeared-out pulses.
"Hidden within an incredibly massive dataset, we found a very peculiar signal, one that matched all the known characteristics of a Fast Radio Burst, but with a tantalizing extra polarization element that we simply have never seen before," said Jeffrey Peterson, a faculty member in Carnegie Mellon's McWilliams Center for Cosmology.
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Until now, only 15 FRBs have been definitively identified, all of which fell within the 1.2-1.5 GHz frequency range. FRB 110523 has a lower frequency, falling within the 700-900 MHz range.
"I feel extremely lucky to have identified the 16th (FRB)," said Hsiu-Hsien Lin, also from Carnegie Mellon, who made the identification of FRB 110523. "Not only is this the first FRB in this frequency range, our FRB has provided us with a great deal of information that help us to better understand this astrophysical phenomenon."
This particular signal appeared like a diamond in the rough. Not only was its signal clear, it also held a polarization fingerprint (called Faraday rotation, a corkscrew-like twist in electromagnetic radiation) from where it was born.
"This tells us something about the magnetic field that the burst traveled through on its way to us, giving a hint about the burst's environment," said Masui. "It also gives the theorists a bit more to work with when they come up with explanations for these bursts."
Measurements of the dispersion delay of FRB 110523 revealed the source of the signal was 6 billion light-years away (it was therefore triggered 6 billion years ago, when the universe was a little over half the age it is now), but additional analysis revealed the size of the source region - it came from another galaxy. But that's not all.
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Even more information was gleaned from the pulse's dispersion delay; it revealed the signal passed through two distinct regions of ionized gas. One of these regions was very close to the source (within the source's galaxy) and most likely "a nebula surrounding the source or the environment near the center of a galaxy."
"Taken together, these remarkable data reveal more about an FRB than we have ever seen before and give us important constraints on these mysterious events," said Masui. "We also have an exciting new tool to search through otherwise overwhelming archival data to uncover more examples and get closer to truly understanding their nature."
This voyage of discovery reminds me of the story behind the first detection of a pulsar in 1967. At the time, the periodic signal coming from the pulsar PSR B1919+21 was mysterious, so astronomers nicknamed it "LGM-1″ - a.k.a. "Little Green Men-1." The signal, however, was quickly identified as a rapidly-spinning neutron star generating powerful radio emissions as it rotated (creating pulses 1.34 seconds apart) and not evidence of an intelligent alien civilization (read the full story here).
Although the source of FRBs is not clear quite yet, it seems their mystery is slowly unraveling and the mechanism may lie deep inside the magnetic hearts of galaxies billions of light-years away.
Sources: Carnegie Mellon, Phys.org