Last spring, while they were hunkered down at home during the first wave of the COVID-19 pandemic, a team of Canadian astronomers was handed an unexpected gift from the cosmos.
On the morning of April 28, the CHIME telescope near Penticton, B.C., picked up a powerful but fleeting blast of radio energy. Researchers who work with the facility say the chance event has allowed them to identify a cause of the mysterious class of signals known as fast radio bursts. The finding paves the way for a more detailed investigation of the phenomenon, which has puzzled astronomers since fast radio bursts were first noticed in 2007.
Fast radio bursts are brief but intense spikes of radio noise that seem to pop off at random and then vanish, leaving few clues to their origins. For example, the event that CHIME picked up on April 28 consisted of a pair of bursts separated by three one-hundredths of a second and lasting only two to five one-thousandths of a second each. Collectively, the event was about 1,000 times more powerful than other bursts CHIME has spotted – a clue that its source was much nearer than others.
“It was clear that it was something extraordinary,” said Ziggy Pleunis, a post-doctoral researcher at McGill University and a member of the CHIME collaboration, made up of scientists at several research institutions in Canada.
Like most of his colleagues, Dr. Pleunis was housebound because of the pandemic. This did not affect CHIME, however, which has no moving parts and does not require a full-time human operator. The telescope consists of four long troughs of metal mesh that continuously gather radio waves as the sky turns overhead, and bounces them up to multiple receivers. This design has made it ideal for catching fast radio bursts, because of the amount of data it collects every 24 hours.
The CHIME team soon determined that the fast radio burst of April 28 was so powerful it had to be coming from within our own Milky Way galaxy, something never before seen. Even better, it originated in a region of the galaxy where astronomers had identified a magnetar – an extremely dense and rapidly spinning object with a powerful magnetic field. Earth-orbiting satellites that detect X-rays were already watching the magnetar. Their observations show that X-rays were released at precisely the same time as the radio burst picked up by CHIME and a collaborating instrument at the Algonquin Radio Observatory in Ontario.
“We could measure the timing very accurately that it lined up perfectly with the X-ray emission,” said Mubdi Rahman, a team member and researcher at the University of Toronto’s Dunlap Institute for Astronomy and Astrophysics. A radio telescope in California also detected the event. The results were revealed on Wednesday in scientific papers published in the journal Nature.
Magnetars form from the imploding cores of giant stars that go supernova, and they have been prime suspects in the search for sources of fast radio bursts. Until now, no one had ever seen a magnetar in our galaxy produce such a burst.
“There’s nothing like having the proverbial smoking gun,” said James Cordes, a professor of astronomy at Cornell University in Ithaca, NY, who is not a member of the CHIME team. He added that the Canadian instrument provided “a really beautiful result" by linking a known type of object with the kind of signals that previously have come from much more distant reaches.
The discovery also helps narrow the possibilities for how magnetars can generate some of the most powerful signals ever observed in the universe. The details may turn out to be a dramatically scaled up version of a solar flare, which occurs when the sun releases magnetic energy. However, Dr. Cordes said, there are at least two possible ways the energy release can occur and generate a fast radio burst. Narrowing those down to a single explanation – if there is only one – will require more observations.
Dr. Pleunis said the result is a major step toward understanding a cosmic phenomenon that has puzzled astronomers. It may also lead to future discoveries, because fast radio bursts can illuminate matter that is along the line of sight as CHIME and other telescopes observe them, which reveals information about the contents of the universe.
“We really want to use fast radio bursts as tools,” he said. “But to do that we need to have an idea of what they are.”
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