We think of supernova explosions as inevitable for large stars. Big star runs out of fuel and gravity collapses.
Astronomers think at least one type of large star did not end with a supernova. The Wolf-Rayet stars were thought to end with a collapse of their core into a black hole. They might become supernovae after all.
Wolf-Rayet stars are massive. They push out their outer layers with a powerful stellar wind at the end of their short lives, rather than simply running out of fuel and exploding.
The surrounding nebula is rich in ionized helium, carbon, and nitrogen. The surface temperature of the remaining star can be over 200,000 K.
Most of the light is in the ultraviolet range, so it's not bright to the naked eye.
Even with the outer layers of a Wolf-Rayet star cast off, the central star is still much larger than the Sun. It's only a matter of time before it becomes a supernova.
The periodic table fusion will eventually run out of fuel and lead to a core-collapse supernova.
We'd never seen a spectrum that matched a Wolf-Rayet star. Astronomers wondered if Wolf-Rayet stars had a death quiet instead of the supernovae.
The idea was that the remaining core would collapse into a black hole if enough outer layers were cast off. There was no need for a giant explosion. There was a silent death.
The study shows that some Wolf-Rayet stars become supernovae. The spectrum of a supernova was looked at by the team.
The spectrum of the supernova had bright emission light, but not hydrogen or helium. The emission lines weren't caused by elements of the supernova directly, when the team looked at the data more closely.
They were part of a large cloud of gas and dust that was moving away from the star at more than 1,500 km/s.
The progenitor star was surrounded by a dense cloud of carbon, nitrogen, and neon, but without the lighter elements of hydrogen and helium. Strong stellar winds must have been the cause of the expansion of the nebula.
The structure of a Wolf-Rayet star is very similar. The first example of a Wolf-Rayet supernova is thought to be SN 2019.hgp. Similar supernovae have also been detected.
It is not clear whether the explosion was a simple supernova or a more complex hybrid process where the upper layer of the star exploded while the core collapsed directly to a black hole. It will take more observations to figure it out.
Some Wolf-Rayet stars don't go silently into the night.
The article was published by Universe Today. The original article should be read.