(ORDO NEWS) — When giant stars die, they explode in powerful supernova explosions. But before doing so, they go through a very strange but short cycle in their lives.
Wolf-Rayet stars were discovered by French astronomers Charles Wolf and Georges Rayet at the Paris Observatory in 1867. They found three stars that had unusually strong emission lines in their spectra, which meant that the elements in these stars were heated to extremely high temperatures.
The mystery of what the Wolf-Rayet stars really were has persisted for more than a century. This is partly due to how rare they are. Even today, astronomers are only aware of 500 of them in the Milky Way (compared to hundreds of billions of all stars in the galaxy).
Today, astronomers refer to a star that is about to die as a Wolf-Rayet star. As large stars – at least 8 to 10 times the mass of the Sun – approach the end of their lives, they switch from fusing hydrogen to fusing helium in their cores.
Due to their extreme mass, helium fusion releases vast amounts of energy. This energy causes the outer layers of the star to swell so much that they separate completely from the star, forming a bubble-like shell of gas around the star.
Eventually this shell will expand even more, creating a nebula. Indeed, many Wolf-Rayet stars are surrounded by such nebulae. But at the same time, the shell catches a lot of light coming from the star, which heats it up and makes the shell glow. This is the source of the strange lines of radiation seen by Wolf and Rayet.
Wolf-Rayet stars are some of the brightest stars in the universe, some of them over a million times brighter than the sun.
But you can’t see them with your own eyes. They are so hot that most of their radiation is in the ultraviolet part of the electromagnetic spectrum, which is invisible to us (but you definitely wouldn’t want to get too close to them).
The Wolf-Rayet phase does not last long, less than a million years. Soon, each of these stars will begin to form iron cores, which will eventually lead to a supernova explosion, completely destroying the star.
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