Massive stars as cosmic engines

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Massive stars comprise all stars initially above 8 solar masses (Msun). Up to about 100 Msun they burn elements in successive, ever-hotter central shells right through to iron, before becoming core-collapse supernovae, leaving a neutron star or black hole remnant depending on the initial mass. Above about 100 Msun they burn only to oxygen in their cores before becoming pair-instability supernovae with complete disruption. Since the radiative output of a normal star goes roughly as the cube of its mass, a single 100 Msun star matches the total radiation output from a million Suns. Above some 20 Msun, massive stars further distinguish themselves by their strong winds, ranging up to a billion times that of the Sun. Thus, although rare and short-lived, massive stars deliver huge quantities of mostly lethal UV radiation and enriched material to the interstellar medium, ready to build more stars and planets like Earth. This was especially important in the early Universe, when the first stars formed were probably all very massive. Clearly, massive stars dominate the ecology of the Cosmos, yet many of their basic parameters remain elusive.