After a decade of bewilderment, astronomers have pinpointed the source of a mysterious blast of radio waves coming from deep outside the Milky Way: a dwarf galaxy located 3 billion light years from Earth.
It’s a remarkable first in the study of what has been a tremendous astronomical puzzle.
Scientists still don’t know what causes these deep space pulses, but locating the galaxy that spawned one brings us closer to figuring out where they come from.
First discovered in 2007, only 18 of these phenomena have ever been detected.
They’re called fast radio bursts, or FRBs, because they occur for just milliseconds; their fleeting nature makes it tough to catch one in action, and even tougher to figure out the exact spot in the sky they’re coming from.
But astronomers got lucky when they found a particular burst known as FRB 121102: it is the only one known to repeat, meaning multiple radio bursts have been detected coming from the same location in the sky.
That makes it easier for scientists to catch again, Shami Chatterjee, an astronomer at Cornell University who discovered the repetition says.
That discovery gave Chatterjee the idea to continually observe FRB 121102 with a huge network of radio telescopes.
And sure enough, he and his team were able to get high-resolution images of multiple bursts after many hours of observation, allowing them to track down the source of FRB 121102.
Their work is detailed today in three studies published in Nature and The Astrophysical Journal Letters.
The mystery of fast radio bursts
When FRBs were first discovered, there was debate over whether or not these signals were actually coming from space at all. Astronomers wondered if they were just bizarre interference of some kind.
But after a closer look, researchers realized FRBs are unique. Typically, a burst of radio waves will have different wave frequencies occurring at once, but FRBs have frequencies that are spread out.
The highest frequencies of each FRB arrive slightly earlier at Earth while the lowest frequencies arrive slightly later.
It’s a sign that the these FRBs are weary travelers, having journeyed through a lot of interstellar gas and plasma that’s mucking up their signals.
And FRB signals are so mucked up that astronomers are convinced they’re coming from outside the Milky Way Galaxy. But that creates another problem: these bursts must come from a super bright source.
“Like absolutely, incredibly bright,” says Chatterjee. Experts have come up with dozens of theories, such as the cataclysmic collision of neutron stars or a black hole tearing itself apart.
But no one has agreed on a single explanation.
Then the discovery of FRB 121102 changed everything. Because of its repeating nature, astronomers know that its source can’t be anything explosive or an object being destroyed.
“Something like that could not repeat again at the same place at the same distance,” says Chatterjee. “So that basically put the end to a huge swath of models.”
Maybe more than one thing is capable of creating FRBs — and that’s why there hasn’t been a single explanation. But the only way to know for sure was to find the host galaxy.
Another possibility is that the FRB is coming from a type of dense neutron star with an incredibly strong magnetic field, called a magnetar.
Astronomers have discovered magnetars in our galaxy that produce bright radio pulses, but nothing as bright as FRB 121101.
So something would have to be amplifying the pulses, like the way a magnifying glass focuses a beam of light on ants.
That may mean blobs of plasma are lining up just right to focus the radio waves on Earth, making them extra bright, says Chatterjee. “This is very plausible,” he says. “We’re not invoking any radical new physics.”
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