Astronomers have spotted more than a dozen new pulses of radio waves coming from outside our galaxy, including a few bursts that stem from the exact same location in the sky. It’s only the second time we’ve found these weird intergalactic flashes, known as fast radio bursts that repeatedly come from one spot in space. This discovery brings us one step closer to figuring out where these weird pulses come from.
Today’s discovery, presented in two papers in the journal Nature, excites astronomers because repeating fast radio bursts, or FRBs, allow astronomers to make multiple observations, to home in on where they’re coming from. Pinpointing their intergalactic origins could help us figure out which objects are likely sending these excited flashes our way.
Most FRBs have been momentary blips in the sky — at least as far as we know. These explosions of radio waves will last for just milliseconds and then disappear, never to be seen again. They seem to come from some incredibly distant spot in the Universe — sometimes billions of light-years away. The first FRB was discovered in 2007, and since then, we’ve confirmed 52 sources of these transient bursts. But in 2015, a special FRB discovery was made when multiple flashes were found that came from the same location. That provided an opportunity to help locate its source, and today’s FRB gives scientists another shot at that goal.
“When these bursts happen once only, it’s really hard to figure out what created them,” Cherry Ng, a radio astronomer at the University of Toronto and lead author on the paper about the repeating FRB, tells The Verge. “Now we’re showing, no, at least one other repeats.”
FRBs also double as tools for observing the Universe. To get to our planet, FRBs pass through vast swaths of space. That space isn’t completely empty: there are tiny bits of matter that fill the regions between galaxies. And what an FRB looks like, or its structure, can tell astronomers exactly how much junk it passed through on its way to Earth. “These FRBs are really one of the only ways we can probe the intergalactic medium,” Shami Chatterjee, an astronomer at Cornell University who found the first repeating FRB but was not involved with this new research, tells The Verge. “And that’s why finding more FRBs is so exciting for us.”
The problem, though, is that detecting FRBs has been an incredible challenge. It’s thought that upwards of 5,000 FRBs pop up every day. But we never know when — or where — they’re going to hit. “It’s like being in a pitch dark room, and you’re being surrounded by these flash bulbs popping off,” Chatterjee says. “They last a millisecond, and then they’re gone.” Oftentimes, finding one is just a matter of luck: looking in the right spot at the right time with a radio telescope.
Last year, a new facility in Canada called CHIME came online, and it’s designed, in part, for FRBs. It’s made up of four long half-pipe shaped dishes, but unlike other radio telescopes, CHIME can’t point. That means these dishes observe the same patch of sky every day. (As the Earth turns, the stars and galaxies in this patch change, but it’s still a relatively limited area.) The hope is that this consistency will allow CHIME to catch multiple FRBs.
There was some concern, however, that CHIME might not see these flashes because the facility looks for waves at lower frequencies — or radio waves that are spaced farther apart. And FRBs are slightly harder to see at low frequencies. When they pass through the Universe, all the stuff they cross through mucks up the waves. As a result, the low-frequency waves get scattered out of the signal or absorbed by the stuff lurking between galaxies. “People were worried that it would be scattered out of existence, all of these pulses,” says Chatterjee.
But between July and October 2018 — before it was at full operation — CHIME spotted 13 different FRBs as well as six from the same location. While it made these observations, new parts were still being installed to the detector, and the whole system was in the midst of being calibrated. Scientists were turning the system on and off just to see if it was working, and that was enough to catch FRBs. Finding a repeating burst so quickly, before the telescope was at full power, suggests they must be common. “There’s a good chance there are many more,” Ng says.
Now that a second repeating FRB has been found, many astronomers wonder if there are two different types of these bursts: ones that repeat and ones that don’t. For instance, the second repeating burst is structured a lot like the first one, Ng says. But only two observations mean it’s too soon to make a rule, and it’s possible that FRBs we’ve observed elsewhere repeat, too, and we just missed it.
Whatever is causing these bursts must be incredibly intense. Each FRB has about 25 million times more energy than our Sun, packed into just a millisecond, according to Chatterjee. “And that’s astounding,” he says. “What is it that is getting that much energy out?” A popular idea is that these bursts are coming from some type of super dense object, like a black hole. Many think they may actually come from a special type of corpse star known as a magnetar, which has a very powerful magnetic field.
To figure out where they’re coming from, we have to watch one flash over and over again. That’s how Chatterjee and his team found the source of the first repeating FRB: a dwarf galaxy 3 billion light-years away. Now, Ng and her team hope to do the same with this new one, and they want other more powerful radio facilities to help out by observing it, too. Already, they have a good sense of where it’s coming from in space. “We know it quite well, but it’s not good enough for saying which galaxy,” she says.
Ng reports only six repeating bursts in the paper, but she says they’ve actually found a few more since the study was written. And with each new one they find, the more we learn about what these FRBs have passed through to get to us. Each one shines light on the structure of our Universe. “They’ve convincingly demonstrated they’re going to be detecting a whole slew of FRBs,” says Chatterjee. “That’s just great news, because the more FRBs we have, the better we can start mapping out the intergalactic medium.”