(Submitted March 06, 2005)
I read that gamma-ray bursts are caused by hypernova explosions
of Wolf-Rayet stars in the distant universe.
Assuming this is correct, wouldn't these
massive stars seem to be more prevalent in a younger Universe?
Under what conditions might these
stars form, and how long would formation take? If formed in the earliest
Universe, wouldn't these stars be less likely to contain initial impurities
of heavier elements?
You can get started by reading the archived answer on our site:
There are more details at
Our page tells you that the Wolf-Rayet stars are massive stars
near the end of their lives. Astronomers are not completely sure how
these stars form, but it is possible that most extremely massive
stars (more than forty times the mass of the sun) become WR stars for
a short time near the ends of their lives. The mean lifetime of WR
stars is estimated at only around 100,000 years and the formation
time (from an existing star) is comparable. The reason there were
probably more WR stars earlier in the universe is because it is
believed that there were more massive stars early on. Stars early in
the universe would initially contain fewer heavier elements than
stars today, but heavy elements are produced inside WR stars and then
distributed throughout their galaxy by the strong winds that WR stars
generate. Thus WR stars are an important contributor to the
enrichment of galaxies by heavy elements.
Hans Krimm for "Ask an Astrophysicist"