A supernova explosion is what happens to most giant stars at the end of their lives. The star’s core runs out of fuel, gravity causes the core to collapse, and an explosion occurs. Some of them turn into black holes before they explode and during the collapse of the nucleus. Is there another end to the big stars?
Wolf-Rayet stars are among the most massive stars known in the universe. These stars were previously thought to turn into black holes at the end of their lives, but a new discovery shows that at the end of their lives – instead of running out of fuel and collapsing – they exterminate their outer layers with enormous internal force. They are scattered in space.
The scattering of these layers produces a new nebula rich in ionized helium, carbon, and nitrogen, but with almost no hydrogen. The nebula has a surface temperature of about 200,000 Kelvin, making it the brightest star known. Since most of this radiance is in the ultraviolet range, they are not visible to the naked eye.
Even as the outer layers of the Wolf-Rayet star are pushed out, the main star is still much more massive than the Sun. So becoming a supernova is still an option. In other words, the star will eventually run out of fuel one day, and the collapse of the nucleus will produce a supernova.
Supernova or nebula?
The point is: we can see the spectrum of elements inside a supernova. However, we have not seen any spectrum that matches the spectrum of the Wolf-Rayet star. This led astronomers to be skeptical of the Wolf-Rayet lifestyle and to consider the silent death of a star without any explosion as a hypothesis.
The research team began studying the SN 2019hgp supernova data collected by the Zwicky Observatory.
The spectrum of this supernova has a bright radiant light that indicates the presence of carbon, oxygen and neon. But there is no hydrogen or helium. This shows that these spectral lines were not created by elements that directly belong to the supernova. Instead, they belong to a nebula moving away from the main star at speeds of more than 1,500 kilometers per second.
In other words, before the supernova exploded, the generating star was surrounded by a nebula rich in carbon, nitrogen, and neon, while lighter elements such as hydrogen and helium were absent. The nebula is thought to have expanded due to strong star winds.
This hypothesis fits well with the structure of the Wolf-Rayet star. However, researchers need to study more supernovae and stars in this method to fully prove their point.