Wolf-Rayet stars have powerful winds, up to 1,000 million times stronger than the solar wind that is seen during a total eclipse, with speeds up to one percent of the speed of light. They violently end their life as core-collapse supernovae, and most likely gamma ray bursts, which are amongst the most powerful events in the universe.
Massive stars play a dominant role in the ecology of their parent galaxies since their stellar winds inject a great deal of material and energy into their environment.
They have received renewed attention in recent years since spectra of high redshift galaxies, witnessed at a time when the universe was only a few billion years old, bear a striking resemblance to nearby starburst galaxies, which themselves show the characteristic wind signatures of hot, O-type stars. However, we are poorly equipped to interpret these important data.
Solely hydrogen and helium were formed in the Big Bang, so that all heavier elements were subsequently created through nuclear reactions in stars. Consequently, the heavy element content (or metallicity) of a young galaxy will be much lower than that of the current Milky Way.
Our surveys of Wolf-Rayet stars within nearby star-forming galaxies have been compared to deep X-ray images to reveal candidates of rare Wolf-Rayet plus black hole or neutron star systems.
Prior to our studies only one Milky Way system was known (Cyg X-3), while we now have confirmed three instances of Wolf-Rayet plus black hole systems (IC10 X-1, NGC300 X-1, M101 ULX-1), whose black hole components are the highest known to date amongst stellar-mass systems.
These findings have been reported by:
NASA for IC10 X-1 (Massive black hole smashes record).
ESO for NGC 300 X-1 (Black hole hunters set new distance record).
Gemini for M101 ULX-1 (Fast, furious, refined: Smaller black holes can eat plenty).
The image above shows an artists impression of these high-mass X-ray binary systems.
NGC 300 X-1 is a Wolf-Rayet/black-hole binary, Crowther et al. 2010.
Evolution and fate of very massive stars, Yusof et al. 2013 MNRAS 433 1114.
Puzzling accretion onto a black hole in the ultraluminous X-ray source M 101 ULX-1, Liu et al. 2013 Nat 503, 500.