Rare dust-shrouded dying star revealed in new JWST image

Giant stars are perhaps the ultimate example of “live fast die young”. Unlike our own Sun, which will shine for billions of years, more massive stars can burn through their thermonuclear fuel in just a few million years before shedding their outer layers and exploding in a dramatic supernova.

This week, NASA unveiled a rare image from the James Webb Space Telescope (JWST) of one such stellar giant – a Wolf-Rayet star in the last, fleeting stages of its life. Named WR 124, it is located in the constellation Sagittarius and is about 15,000 light-years from Earth. The dying star is at least 30 times the mass of our Sun, but is shrinking rapidly as it blows hot gas into the cold vacuum of space.

“We caught it early on,” said Anthony Moffat, a retired astrophysicist who previously observed WR 124 with the Hubble Space Telescope and was not involved in the recent JWST measurements. Moffat has been studying Wolf-Rayet stars for decades. “It’s the youngest I know,” he says. The colorful cloud in the image — somewhat misleadingly called a planetary nebula — is only a few thousand years old. Now “the nebula embraces the star,” he says. But over time it will bloom outward in expanding shells, or rings, of gas and dust.

Stars are nature’s fusion reactors, glowing from the energy released by the fusion of hydrogen into helium atoms. Once massive stars have burned all their hydrogen, they begin to fuse helium into heavier elements – through a more energetic fusion reaction that creates powerful stellar winds. These winds, blowing away at speeds in excess of 150,000 kilometers per hour, carry the star’s outer layers with them and hurl enormous amounts of gas and dust into space.

This gas glows with infrared radiation, the same type of light that JWST detects. Astrophysicists created the spectacular image by combining data from two JWST instruments, the Near-Infrared Camera (NIRCam) and the Mid-Infrared Instrument (MIRI). The Hubble Space Telescope, which mainly collects light at optical wavelengths, had previously captured images of WR 124, but JWST’s observations reveal the star’s burgeoning nebula in stunning new detail.

“Personally, the most exciting part of this image is that we’re capturing a rare event — namely, a Wolf-Rayet star — with a level of detail that can only be achieved with JWST,” says Macarena Garcia Marin, an astrophysicist at the European Space Agency who is working with MIRI works together.

Only massive stars can go through the Wolf-Rayet phase, and not all do. Astronomers have estimated that there are only 1,000 Wolf-Rayet stars in our galaxy – 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 millions of times as bright as the Sun, says Moffat. “What they lack in numbers they make up for in light,” he adds.

“This dust will spread throughout the cosmos and will eventually create planets. And that’s actually how we got here,” NASA astrophysicist Amber Straughn said in a panel discussion at the 2023 South by Southwest Conference in Austin, Texas, where the image was first unveiled. “I think that’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 of it in the universe than scientists can explain from a simple cataloging of obvious sources. “It’s always an interesting place to be in science when our theories don’t match our observations — and that’s where we are with dust right now,” says Straughn. These detailed images of a dying star dissolving as it forges heavy elements and creates copious amounts of dust can help scientists refine their understanding of this fundamental process.

One day – thousands or even millions of years from now, but essentially tomorrow on galactic scales – WR 124 will explode in a spectacular supernova. In addition to the abundance of dust and heavy elements, the explosion could leave behind a black hole. But physicists don’t have a great way to predict this with certainty. Moffat suspects the supernova remnant could stall as a neutron star instead — the last stop before a collapsing star reaches a black hole’s ultimate oblivion. Without a look from an observatory far in the future for us, we may never know what the outcome is for WR 124. But either way, his ultimate destiny remains the same, written in the stars and planets yet to form from his bounty of cosmic dust.