By Tom Burns
Recently, the James Webb Space Telescope created an image of WR 124, a Wolf-Rayet (WR) star undergoing its death throes.
You can see the image by visiting https://astrobiology.com/2023/03/wolf-rayet-star-wr-124-dust-contains-materials-needed-for-life.html.
You’ll see a bright star with streamers and knots of glowing gas around it. The ensemble looks very much like a single exploding fireworks display. Its texture resembles the delicate tendrils of a dandelion recently gone to seed.
WR 124 is about 20,000 light-years away. (One light-year is equivalent to about six trillion miles.)
When astronomers look at the spectrum of Wolf-Rayet stars, they can analyze their composition. They see the spectral signatures of helium, nitrogen, carbon, and oxygen, telltale signs that such stars have exhausted most of their thermonuclear fuel and will soon die by collapsing into a black hole.
Stars like our sun are thermonuclear furnaces exploding with the power of hundreds of billions of hydrogen bombs every second. Massive amounts of energy stream into the space around the stars.
The force exerted by that energy, a phenomenon that astronomers call radiation pressure, causes an outflow of atomic and subatomic particles called a stellar wind.
The sun generates a considerable stellar wind. However, our slightly below-average star is a piker compared to the power of WR 124.
WR 124 has a mass of about 30 times that of our sun. At about 12 times the sun’s diameter, WR 124 is around 12 million miles wide. Yet, it is producing an astounding 565,000 times more energy than old Sol.
The sun has a relatively mild surface temperature of about 10,000 degrees Fahrenheit. WR 124’s surface reaches a scalding 80,000 degrees.
When the sun dies in five billion years, it will gently shed its outer layer and form a shell of gas around itself called a planetary nebula.
WR 124 colossal energy eruption generates significantly greater outward-pushing force than the sun.
In the case of our early solar system, the sun’s comparatively weak radiation pressure was enough to drive light gasses like hydrogen and helium into the outer solar system. That process allowed rocky planets like Earth to form without hydrogen/helium atmospheres.
In WR 124’s case, its considerable radiation pressure produces an enormous outflow of material from the star’s outer shell. As a result, WR 124 generates an outward-moving cloud of hot gas and dust called a Wolf-Rayet nebula.
The nebula is expanding at 93,000 miles per second. WR 124 degenerated from its previous status as a supergiant star only 20,000 years ago. Since then, the nebula has expanded into a complex system about 36 trillion miles (about six light-years) wide. Shine a flashlight on one side of the nebula, and the light will take six years to reach the other side.
Stars with masses over eight times the sun inevitably collapse into black holes. That collapse is usually preceded by an enormous supernova explosion.
However, some astronomers argue that WR 124 may not suffer such an explosive end to its life. Its stellar wind has already blown away ten solar masses of material in the 20,000 years since it entered Wolf-Rayet mode. If it loses another 12 solar masses in the few hundred thousand years before it dies, it will still collapse but might not explode as a supernova.
In the meantime, its WR 124’s energy eruption has produced a glorious glowing firework, a shape exclusive to it. Every Wolf-Rayet star’s expanding nebula takes on a unique shape as its chaotic stellar wind heaves outward.
In the case of WR 124, we see the delicate texture of dandelion tendrils, but other WR stars generate far different nebular structures. Witness, for example, the Thor’s Helmet nebula in the constellation Sagitta.
You’ll have little chance of seeing WR 124 and its attendant nebula for yourself, no matter how big your telescope is. It’s simply too faint and too far away.
However, one Wolf-Rayet nebula is a favorite of amateur telescopists everywhere — the Crescent Nebula in the constellation Cygnus. I managed to glimpse it as a thin, broken bubble of light one fine summer night using my telescope with an eight-inch-diameter mirror and a nebular filter.
I will never forget thinking, “How can such incredible violence drive such delicate beauty?” But, of course, that’s the way of Wolf-Rayet stars.
Tom Burns is the former director of the Perkins Observatory in Delaware.