Astronomers have imaged the largest stellar bubble in our galaxy.
This image, captured by the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, shows the expanding outer layers of red supergiant DFK 52. ALMA collects radiation invisible to our eyes, near the boundary between infrared and microwave radiation. In this false-color image, parts of the bubble moving away from us are shown in red; material moving toward us is shown as blue.
Credit: ALMA (ESO/NAOJ/NRAO)/M. Siebert et al.
Astronomers from Chalmers University of Technology, Sweden, have discovered a huge expanding bubble of gas and dust surrounding a red supergiant star. It’s the largest structure of its kind ever seen in the Milky Way. The bubble was blown into space around 4000 years ago. The question scientists are asking is, “Why did the star survive?”
The results are published in the scientific journal Astronomy and Astrophysics. The team, led by Mark Siebert of Chalmers, used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to observe the star DFK 52, which lies in the massive star cluster Stephenson 2 in the constellation Scutum the Shield.. This red supergiant is similar to the well-known star Betelgeuse in Orion the Hunter.
“We got a big surprise when we saw what ALMA was showing us. The star is more or less a twin of Betelgeuse, but it’s surrounded by a vast, messy bubble of material,” said Siebert.
The bubble, a complex of clouds of gas and dust, is as massive as the Sun and extends out 1.4 light-years from the star. That’s thousands of times wider than our own solar system. Astronomers have pegged the distance to DFK 52 as 19,500 light-years. If the star were as close to us as Betelgeuse is (640 light-years), the bubble would span a third of the Full Moon’s width.
“The bubble is made of material that used to be part of the star. It must have been ejected in a dramatic event, an explosion, that happened about 4,000 years ago. In cosmic terms, that’s just a moment ago,” says Elvire De Beck, astronomer at Chalmers.
Will the star become a supernova?
Why DFK 52 shed so much mass without exploding as a supernova is still unclear. One possibility is that the star has a hidden companion that helped it cast off its outer layers.
“To us, it’s a mystery as to how the star managed to expel so much material in such a short timeframe. Maybe, like Betelgeuse seems to, it has a companion star that’s still to be discovered,” said Siebert.
Red supergiants like DFK 52 are nearing the ends of their lives and are expected to eventually explode as supernovae. So, this star could be nearing that time, although we couldn’t predict when it would happen.
“We’re planning more observations to understand what’s happening — and to find out whether this might be the Milky Way’s next supernova. If this is a typical red supergiant, it could explode sometime in the next million years,” says Elvire De Beck.
