Strange Radio Bursts Coming From Deep Space
Something has breathed new life into a far away cosmic mystery machine and caused it to repeatedly hurl tremendous amounts of energy into the void.
It’s not clear exactly what that object is, but scientists refer to the observable phenomenon as a fast radio burst: a fleeting but extremely powerful blast of radio waves. In this case, astronomers caught a rapid stream of radio bursts coming from a galaxy about three billion light-years away.
Scientists with the Breakthrough Listen project made the discovery because, fortunately, they had a pretty good idea where to look. The team had tuned the giant Green Bank Telescope in West Virginia to a spot on the sky where a fast radio burst known as FRB 121102 had previously been singing to the stars.
The Green Bank Observatory in West Virginia is home to the largest fully steerable telescope in the world. Using data from Green Bank, scientists are able to study the faintest radio objects in the universe.
Of the roughly two dozen bursts discovered so far, FRB 121102 is the only one known to play on repeat. Because of that, it’s the only burst with a known home galaxy, which was identified in late 2016 after scientists used several telescopes to pinpoint its origin.
After that discovery, FRB 121102 fell silent for a good stretch of 2017. Though it had previously offered periods of quiescence and activity before, its silence was alarming.
“We feared that our opportunity to study it has passed,” says UC Berkeley’s Casey Law. “This new detection suggests that FRB 121102 is coming back into an active state and will be easier to study how and what is producing these powerful bursts.”
STRANGE RADIO
First identified in 2007, fast radio bursts are still fundamentally enigmatic. Scientists don’t know what powers them, but they do know the blasts come from very, very far away and occasionally from sites with fantastically strong magnetic fields.
Designed to search the skies for signs of intelligent radio transmissions, the Breakthrough Listen team took aim at FRB 121102 to help them test equipment for that search. They also wanted to understand, among other things, how narrow, pulsed signals are modified as they travel through interstellar plasmas and other intergalactic junk.
A Hubble Space Telescope image shows the unprecedented detail of the Antennae galaxies, an intense star-forming region created when two galaxies began to collide some 200 million to 300 million years ago. The bright, blue-white areas show newly formed stars surrounded by clouds of hydrogen, which are colored pink. A similar collision is expected between our galaxy, the Milky Way, and the nearby Andromeda galaxy in several billion years.
The Andromeda galaxy, also known as Messier 31, is the largest neighboring galaxy to the Milky Way. This photo, a mosaic of ten images captured by the Galaxy Evolution Explorer spacecraft in 2003, shows blue-white regions along the galaxy’s arms where new stars are forming and a central orange-white area containing older, cooler stars.
This false-color view of the Cartwheel galaxy was created by combining images captured by four space telescopes: Galaxy Evolution Explorer,Hubble Space Telescope, Spitzer Space Telescope, and Chandra X-ray Observatory. Astronomers think a smaller galaxy, possibly one of two galaxies seen here (bottom left), passed through the center of the Cartwheel galaxy about 100 million years ago.
Sheets of debris from an exploded star swirl in the Large Magellanic Cloud (LMC) galaxy in this Hubble Space Telescope image. At a distance of about 180,000 light-years, the LMC galaxy is a relatively close neighbor of the Milky Way. It can be spotted from the Earth’s Southern Hemisphere without a telescope.
This 2008 illustration shows a revised look at our galaxy, the Milky Way. Scientists studying infrared images from NASA’s Spitzer Space Telescope determined our galaxy’s spiral has two major and two minor arms instead of four major arms, as was previously thought. The demoted arms can be seen as faint trails between the major arms, which emanate from the ends of the orange central bar.
The Black Eye or Evil Eye galaxy gets its nicknames from the band of light-absorbing dust that appears in front of the star system’s bright center in this Hubble Space Telescope image. Messier 64, as the Black Eye galaxy is more formally known, is thought to have taken on its ominous appearance after it collided with another galaxy perhaps a billion years ago.
Two merging galaxies located 140 million light-years from Earth resemble a giant celestial mask in this false-color image. The ice-blue eyes are actually the galaxies’ cores, and the mask is their spiral arms. The galaxies, called NGC 2207 and IC 2163, began their gravitational tango about 40 million years ago and will eventually meld into one.
An infrared image of the Messier 82 galaxy, nicknamed the “Cigar galaxy,” shows the formation’s central plane in blue and white, with a halo of smoky dust in red. This red cloud, composed of hydrocarbon dust similar to car exhaust, is being blown out into space by the galaxy’s millions of young stars.
This image of the Whirlpool galaxy shows the classic features of a spiral galaxy: curving outer arms where newborn stars reside and a yellowish central core, home to older stars. A companion galaxy called NGC 5195, seen here at the tip of one of Whirlpool’s arms (right), has been passing by for hundreds of millions of years and exerting gravitational forces on its larger neighbor.
A color-composite image shows the NGC 300 galaxy, a spiral galaxy like the Milky Way located about seven million light-years from Earth. In this image, young, hot stars are the blue dots that comprise much of the outer arms. Older stars are in the middle and appear yellow-green.
Billows of cosmic dust swirl amid NGC 1316, a giant elliptical galaxy formed billions of years ago when two spiral galaxies merged. Astronomers examined red star clusters within NGC 1316 to determine that the massive galaxy was indeed created by a major celestial collision.
A composite image of the Messier 81 (M81) galaxy shows what astronomers call a “grand design” spiral galaxy, where each of its arms curls all the way down into its center. Located about 12 million light-years away in the Ursa Major constellation, M81 is among the brightest of the galaxies visible by telescope from Earth.
After all, those types of signals are among the main emissions the team expects from extraterrestrial civilizations, says Andrew Siemion, director of the Berkeley SETI Research Center.
For a while, though, FRB 121102 seemed to have run out of steam. Then, when the Breakthrough team took a look on August 26, they saw 15 bursts within an hour of observing—the most FRB 121102 had produced since this time last year. They also caught the bursts coming in at the highest frequencies yet seen, which could suggest a large amount of variability in its emission.
No one knows why FRB 121102 has turned on again, or if this new round of bursts is a clue about the astrophysical engine driving the phenomenon. Some scientists suspect it doesn’t have much to do with what powers the object and instead depends on the various cosmic lenses that periodically magnify its songs.
With FRB 121102, “we’ve seen ‘burst storms’ before, including last August through September when the Very Large Array came up empty, empty, empty, and then boom, there it was at every session,” says Cornell University’s Shami Chatterjee.
“The month coincidence has also raised eyebrows,” he says. ”Are we more likely to see bursts during particular seasons, when the lensing geometry lines up just so? This is as yet wild, wild speculation—people apologizing for bringing it up—but who knows.”
Even wilder speculation swirls around the source of fast radio bursts, which refuses to reveal itself. Early theories include primordial black holes, colliding neutron stars, and even some idle talk about extraterrestrial civilizations, though aliens are not an explanation that’s generally taken seriously.
“We agree with the majority of the astronomical community that the likelihood of ET being involved in this source is low, but the source is nevertheless very mysterious,” Siemion says. “We know, without a doubt, that the universe is capable of giving rise to technologically capable life. We would be remiss as scientists to exclude this possibility a priori.”
Now, more serious investigations are focused on magnetars, the extremely magnetic, fantastically dense corpses of exploded stars. These rotating neutron stars launch humongous flares into the cosmos, but whether those flares are somehow linked to the barrage of radio waves is still a mystery.
It’s also possible that FRB 121102 is so active it could have exhausted the total magnetic energy in a magnetar, Law says. “That is a stupendous amount of energy being emitted.”
