Giant stars may be the ultimate example of “live fast, die young”. Unlike our own sun, which will shine for billions of years, more massive stars can burn up their thermonuclear fuel in just a few million years before shedding their outer layers and exploding in a spectacular supernova.
This week NASA unveiled a rare image from the James Webb Space Telescope (JWST) of one of these stellar giants – a Wolf-Rayet star in the last fleeting stages of its life. Named WR 124, it is in the constellation Sagitta and is approximately 15,000 light years from Earth. The dying star is at least 30 times the mass of our sun, but is rapidly shrinking as it spews hot gas into the cold vacuum of space.
“We detected it early,” says Anthony Moffat, a retired astrophysicist, who previously observed WR 124 using the Hubble Space Telescope and was not involved in recent JWST measurements. Moffat has studied Wolf-Rayet stars for decades. “He’s the youngest I know,” he said. The colorful cloud in the image, misleadingly called a planetary nebula, is only a few thousand years old. Now, “the nebula is hugging the star,” he says. But as time passes, it will blossom into expanding shells or rings of gas and dust.
Stars are nature’s fusion reactors, glowing with the energy released by the fusion of hydrogen to form helium atoms. Once massive stars have burned up all their hydrogen, they begin to fuse helium into heavier elements, through a more energetic fusion reaction that raises powerful stellar winds. Blowing away at speeds in excess of 150,000 kilometers per hour, these winds drag the outer layers of the star with them, ejecting huge volumes of gas and dust into space.
This gas emits infrared radiation, the same type of light that JWST detects. Astrophysicists created the dramatic image by combining data from two of JWST’s instruments, the Near Infrared Camera (NIRCam) and the Mid Infrared Instrument (MIRI). The Hubble Space Telescope, which primarily collects light at optical wavelengths, had previously captured images of WR 124, but JWST observations show the star’s booming nebula in stunning new detail.
“Personally, the most exciting part of this image is that we are capturing a rare event – i.e. a Wolf-Rayet star – in a level of detail that can only be achieved with JWST,” says Macarena. Garcia Marin, astrophysicist at the European Space Agency, who works with MIRI.
Only massive stars can undergo the Wolf-Rayet phase, and not all of them do. Astronomers have estimated that there are only 1,000 Wolf-Rayet stars in our galaxy, or about one in 100 million. The closest is about 1,000 light-years away in the Gamma Velorum star system, visible from the southern hemisphere. Wolf-Rayet stars can be a million times brighter than the sun, Moffat says. “What they lack in number, they make up for in light,” he adds.
“This dust is spreading throughout the cosmos and will eventually create planets. And that’s how we got here, actually,” NASA astrophysicist Amber Straughn said during a panel discussion at the 2023 South by Southwest conference in Austin, Texas, where the image was taken. revealed for the first time. “I think it’s one of the most beautiful concepts in all of astronomy.”
But while we’re all made of stardust, there seems to be a lot more in the universe than scientists can explain from a basic cataloging of obvious sources. “It’s always interesting to be in science when our theories don’t match our observations — and that’s where we’re at right now with the dust,” Straughn says. These detailed images of the outcome of a dying star, as it forges heavy elements and generates abundant dust, can help scientists refine their understanding of this fundamental process.
One day – thousands, if not millions of years from now, but essentially tomorrow on a galactic scale – WR 124 will explode into a spectacular supernova. Besides the wealth of dust and heavy elements, the explosion could leave a black hole. But physicists don’t have a great way to predict this with certainty. Moffat speculates that the supernova remnant might instead come to a halt like a neutron star – the last stop before a collapsing star reaches ultimate oblivion as a black hole. Without a glimpse of an observatory that, for us, remains in the distant future, we may never know what outcome occurs for WR 124. But either way, its ultimate fate remains the same, written in the stars and the planets yet to be formed from his bountiful gift of cosmic dust.