Wolf–Rayet star

Wolf–Rayet stars, often abbreviated as WR stars, are a rare heterogeneous set of stars with unusual <a href="/facts/Spectroscopy/mj71FuNK">spectra</a> showing prominent broad emission lines of ionised <a href="/facts/Helium/yRul93TG">helium</a> and highly ionised <a href="/facts/Nitrogen/Nf1QpGDz">nitrogen</a> or <a href="/facts/Carbon/ukrgQexo">carbon</a>. The spectra indicate very high surface enhancement of <a href="/facts/Stellar_nucleosynthesis/qEQJdJe6">heavy elements</a>, depletion of hydrogen, and strong <a href="/facts/Stellar_wind/bn5J6vpx">stellar winds</a>. The <a href="/facts/Effective_temperature/RY30DaSY">surface temperatures</a> of known Wolf–Rayet stars range from 20,000 <a href="/facts/Kelvin_(unit)/E3trzC4C">K</a> to around 210,000 <a href="/facts/Kelvin_(unit)/E3trzC4C">K</a>, hotter than almost all other kinds of stars. They were previously called W-type stars referring to their <a href="/facts/Stellar_classification/dYrIuK9H">spectral classification</a>.
Classic (or <a href="/facts/Population_I/8ur1qDRK">population I</a>) Wolf–Rayet stars are <a href="/facts/Stellar_evolution/Qa4vAGmn">evolved</a>, massive stars that have completely lost their outer <a href="/facts/Hydrogen/BoYHjl0J">hydrogen</a> and are <a href="/facts/Nuclear_fusion/hP0gLDqj">fusing</a> helium or heavier elements in the core. A subset of the population I WR stars show hydrogen lines in their spectra and are known as WNh stars; they are young extremely massive stars still fusing hydrogen at the core, with helium and nitrogen exposed at the surface by strong mixing and radiation-driven mass loss. A separate group of stars with WR spectra are the central stars of <a href="/facts/Planetary_nebula/5Vy84cPq">planetary nebulae</a> (CSPNe), post-<a href="/facts/Asymptotic_giant_branch/R90sd1Hl">asymptotic giant branch</a> stars that were similar to the <a href="/facts/Sun/CadPCVHh">Sun</a> while on the <a href="/facts/Main_sequence/DJ3Wq8kd">main sequence</a>, but have now ceased fusion and shed their atmospheres to reveal a bare carbon-oxygen core.
All Wolf–Rayet stars are highly luminous objects due to their high temperatures—thousands of times the <a href="/facts/Bolometer/5YlzCoe8">bolometric</a> <a href="/facts/Luminosity/1tdhpk9l">luminosity</a> of the Sun (L☉) for the CSPNe, hundreds of thousands L☉ for the population I WR stars, to over a million L☉ for the WNh stars—although not exceptionally bright visually since most of their <a href="/facts/Electromagnetic_radiation/Ynx7ujCW">radiation</a> output is in the <a href="/facts/Ultraviolet/kncBUqn5">ultraviolet</a>.
The naked-eye star systems <a href="/facts/Gamma_Velorum/twRat1rc">γ Velorum</a> and <a href="/facts/Theta_Muscae/fg8bsIgF">θ Muscae</a> both contain Wolf-Rayet stars, and two of the <a href="/facts/List_of_most_massive_stars/IJS4vLlo">most massive known stars</a>, <a href="/facts/BAT99-98/o8E8WDwC">BAT99-98</a> and <a href="/facts/R136a1/4kMEN0aX">R136a1</a> in <a href="/facts/30_Doradus/nkrNzh6I">30 Doradus</a>, are also Wolf–Rayet stars.

Wolf–Rayet star open-in-new

Wolf–Rayet star