Magnetic Secrets of Mysterious Radio Bursts in a Faraway Galaxy
Posted January 10, 2018 4:39 p.m. EST
Snap, crackle or pop?
Nature keeps coming up with new and baffling ways to blow things up.
Astronomers have been baffled lately by the mysterious pulses of cosmic energy known as fast radio bursts that seem to pepper the cosmos. In a few unpredictable milliseconds, they typically emit as much energy as the sun does in a day. About 30 of these objects have been discovered deep in space since the first was detected in 2007, all but one burping out a cataclysmic radio pulse exactly once and then disappearing into the night.
Only one burster, known as FRB121102, after the date it was discovered (Nov. 2, 2012), has repeated itself, hundreds of times now.
That allowed Shami Chatterjee of Cornell and his colleagues to track it to a galaxy 3 billion light years away. But that only deepened the mystery of the powers of these objects, and why none are closer to us.
Among the more out-there explanations proffered was that they are lasers propelling alien interstellar spacecraft. That is a scheme that Earthlings themselves are considering to launch a fleet of miniature space probes to Alpha Centauri later this century.
Alas for E.T., new observations have now debunked alien technology as the explanation for at least one source of a burst, according to a new paper in Nature by Jason Hessels of the University of Amsterdam and a multinational crew of radio astronomers.
As monitored by the mighty 300-meter-diameter radio telescope at Arecibo Observatory in Puerto Rico and abetted by measurements at the Green Bank Telescope in Green Bank, West Virginia, the signals from the repeating burster FRB110212 bore the marks of having been produced in a magnetic field at least thousands of times more powerful than normally seen in space.
Those fields and other details of the radio measurements point the finger at the usual suspects of cosmic violence — black holes or neutron stars, the shrunken dense corpses of dead stars, the authors say. Although the facts would imply that these pathological objects of fascination and dread are up to tricks that astrophysicists have not yet conceived.
“It’s a neat result,” Chatterjee wrote in an email. “We’re doing remote sensing of the environment of the fast radio burst source at a distance of 3 billion light years!”
The key is that the radio waves were highly polarized, the light waves vibrating up and down in only one direction, as if viewed through powerful glare-reducing sunglasses. But each wavelength of light was vibrating at a different angle, a telltale sign of an effect called Faraday rotation, in which a magnetic field twists the orientation of electromagnetic waves as they pass through.
When the burst was emitted, Chatterjee explained, it was polarized with all the wavelengths of light lined up and marching in step. But as it traveled, the magnetic field twisted them apart.
One attractive explanation, he said, was that the bursts are produced by a neutron star near a massive black hole. Or an apocalyptically magnetized neutron star called a magnetar, blazing forth in a cloud within the blown-off remains of its former star.
“But it would have to be unlike anything else seen in our galaxy, by orders of magnitude,” Chatterjee said.
“So we can’t really rule out more exotic models, and theorists have a lot of those,” he added, and rattled off possibilities including the tubes of primordial energy called cosmic strings and the mysterious dark matter that makes up a quarter of the universe. “Because why not? It’s still a bit of a mystery.”
Snap, crack and pop indeed. So it isn’t turning out to be a great year for E.T. — at least not so far.
Early in January, astronomers monitoring an enigmatic object known as Boyajian’s Star, after the astronomer Tabetha Boyajian, concluded that erratic and striking dips in its brightness were not caused by some gigantic alien construction project.
The dips — much greater than would be expected for a planet — were discovered by a group of citizen astronomers known as the Planet Hunters, who were following up on results from the Kepler spacecraft. The discovery had elicited suggestions that the dips could be caused by the construction of a Dyson-like sphere, a shell that an advanced civilization might build around its star in order to capture all its energy.
But new observations by Boyajian, of Louisiana State University, and other astronomers of a recent dimming showed that the amount of dimming depended on the wavelength, or color, of the light observed, a classic indication that the obscuring material is not solid but most likely dust.
Now another fantasy of extraterrestrial engineering is biting the dust. Sorry, E.T.