Observations in the first year of use quadruple the number of known radio bursts, revealing two types: one-off and repeaters.
To spot a fast radio burst, you have to be extremely lucky in where and when you aim your radio dish. Fast radio bursts, or FRBs, are strangely bright flashes of light, registering in the radio band of the electromagnetic spectrum, which flare up for a few milliseconds before disappearing without a trace.
These short and mysterious beacons have been observed in different and distant parts of the universe, as well as in our own galaxy. Their origin is unknown and their appearance is unpredictable. Since the first was discovered in 2007, radio astronomers have observed only about 140 eruptions in their telescope.
Now, a large stationary radio telescope in British Columbia has nearly quadrupled the number of fast radio bursts detected so far. The telescope, known as CHIME for the Canadian Hydrogen Intensity Mapping Experiment, has detected 535 new fast radio bursts during its first year of use, between 2018 and 2019.
Scientists with the CHIME collaboration, including researchers from MIT, collected the new signals in the telescope’s first FRB catalog, which they will present this week at the American Astronomical Society Meeting.
The new catalog significantly expands the current library of known FRBs and already provides clues about their properties. For example, the newly discovered eruptions seem to fall into two different classes: those that repeat and those that don’t. Scientists identified 18 FRB wells that burst repeatedly, while the rest appear to be one-off. The repeaters also look different, with each burst taking a little longer and transmitting more focused radio frequencies than bursts of single, non-repeating FRBs.
These observations strongly suggest that repeaters and one-time objects arise from separate mechanisms and astrophysical sources. With more observations, astronomers hope to pinpoint the extreme origins of these curiously bright signals soon.
“Before CHIME, there were fewer than 100 FRBs discovered in total; now, after a year of observation, we’ve discovered hundreds more,” said CHIME member Kaitlyn Shin, a graduate student in MIT’s Department of Physics. “With all of these resources, we can really get a sense of what FRBs look like as a whole, what astrophysics make these events possible, and how they could be used to study the universe in the future.”
CHIME consists of four massive cylindrical radio antennas, about the size and shape of snowboarding halfpipes, located at the Dominion Radio Astrophysical Observatory, operated by the National Research Council of Canada in British Columbia, Canada. CHIME is a stationary array, with no moving parts. The telescope receives radio signals from half the sky every day as the Earth rotates.
While most radio astronomy is done by rotating a large dish to focus light from different parts of the sky, CHIME stares motionless at the sky and focuses incoming signals using a correlator – a powerful digital signal processor that can work through massive amounts. . data, at a speed of about 7 terabits per second, which is equivalent to a few percent of the world’s Internet traffic.
“Digital signal processing allows CHIME to reconstruct and ‘see’ in thousands of directions at once,” said Kiyoshi Masui, an assistant professor of physics at MIT who will lead the group’s conference presentation. “That helps us detect FRBs a thousand times more often than a traditional telescope.”
In the first year of the operation, CHIME detected 535 new fast radio bursts. When the scientists mapped their locations, they found that the eruptions were evenly distributed in space and appeared to be coming from all parts of the sky. From the FRBs CHIME could detect, the scientists calculated that bright high-speed radio bursts occur at a rate of about 800 per day across the entire sky — the most accurate estimate of the total frequency of FRBs to date.
“That’s the beauty of this field — FRBs are really hard to see, but they’re not uncommon,” said Masui, who is a member of MIT’s Kavli Institute for Astrophysics and Space Research. “If your eyes could see radio flashes the way you can see camera flashes, you’d see them all the time if you just looked up.”
Mapping the Universe
As radio waves travel through space, any interstellar gas, or plasma, may distort or scatter the wave’s properties and trajectory along the way. The extent to which a radio wave is spread can provide clues as to how much gas it has passed through and possibly how much distance it has traveled from its source.
For each of the 535 FRBs CHIME detected, Masui and colleagues measured its distribution and found that most of the eruptions likely originated from distant sources in distant galaxies. The fact that the eruptions were bright enough to be detected by CHIME suggests that they must have been produced by extremely energetic sources. As the telescope detects more FRBs, scientists hope to pinpoint exactly what kinds of exotic phenomena can generate such ultra-bright, ultra-fast signals.
Scientists also plan to use the eruptions and their distribution estimates to map the spread of gas throughout the universe.
“Each FRB gives us some information about how far they have spawned and how much gas they have propagated,” Shin says. “With large numbers of FRBs, hopefully we can figure out how gas and matter are distributed on a very large scale in the universe. So in addition to the mystery of what FRBs themselves are, there is also the exciting potential for FRBs as powerful cosmological probes in the future.”
This research was supported by several institutions, including the Canada Foundation for Innovation, the University of Toronto’s Dunlap Institute for Astronomy and Astrophysics, the Canadian Institute for Advanced Research, McGill University and the McGill Space Institute through the Trottier Family Foundation, and the university of British Columbia.