Astronomers have discovered the remains of nearly two dozen exploding stars in the Milky Way, thanks to detailed radio observations that could unveil many more such events in the Galaxy.
A star in the Milky Way is expected to explode as a supernova roughly at least once every 100 years. These violent explosions — the dramatic final throes of massive stars as they exhaust their fuel — can eject vast clouds of dust and gas to locations many light years from the star. Such ‘supernova remnants’ can persist for thousands of years before dissipating. Studying these remnants can reveal useful information about the Galaxy, because they often contain heavy elements that give rise to other stars, planets and even life itself.
Hundreds of such remnants have been found across the Milky Way, but astronomers think that they have observed only about one-fifth of the total number. Most are found by detecting radio emissions from the remnants as they expand, revealing their otherwise invisible shapes, but many are too faint to be picked up. “There’s this missing supernova-remnant problem,” says Brianna Ball, who studies astronomy at the University of Alberta in Edmonton, Canada. “We know how many we should see, and we see a lot fewer than that.”
On 16 January, however, a project led by Ball revealed a new way to track supernova remnants down. It combined the observing power of the Australian Square Kilometre Array Pathfinder (ASKAP), a radio telescope comprising 36 antennas in Western Australia, with that of the Parkes Observatory, a single dish in New South Wales, Australia, to detect previously unseen supernova remnants in a patch of night sky.
“We discovered 21 new candidates,” says Roland Kothes, a radio astronomer at the National Research Council of Canada, who is based in Penticton and Ball’s supervisor. “This image was the first test that we did, and it worked spectacularly well,” he says. The work has yet to be published.
The image the team released contains about five of the 21 newly discovered supernova remnants, including one shaped like a figure of eight, seen faintly in the top left. The picture was taken along one of the spiral arms of the Milky Way, the Norma Arm, near the dense Galactic Centre, where dust and gas heavily obscure visible light.
Finding new remnants can tell us more about “the kinds of stars that explode as supernovae”, says Carlos Badenes, an astronomer at the University of Pittsburgh in Pennsylvania, who studies supernova remnants. “It’s really fantastic that these guys are doing this.”
ASKAP began a five-year survey of the entire sky of the Southern Hemisphere, which accounts for half of the visible Galaxy, last year. That should turn up many more supernova remnants. “We’re detecting sources that previous telescopes might not have been able to detect because they didn’t have the resolution or sensitivity,” says Ball. “We’re hoping it will uncover a large population.”