Early-type Stars
The ubiquity of rapidly expanding stellar winds from OB stars is one of the most unexpected and important discoveries of the early NASA space program. X-rays from O and B stars are thought mainly to arise from their massive supersonic winds, either in radiatively driven shocks, shocks from colliding winds in binaries, or perhaps from dissipation of energy in wind-embedded magnetic fields. Similar processes to those occuring in OB stars winds are probably relevant for the fast outflows widely seen in black hole accretion systems that might be partially or wholly accelerated radiatively through disk emission.
Nancy Evans, Fred Seward, Vinay Kashyap, Jeremy Drake, Joy Nichols
The Chandra X-ray Observatory image and spectrum of the Orion belt supergiant binary zeta Ori. The spectrum of the O9.7 Ib zeta Ori A shows signatures of a relatively high-density plasma, rather than the Doppler-broadened line profiles and strengths expected from a low-density shocked outflow. These results challenge ideas that X-rays from massive stars arise from shocks in their radiatively-driven winds and instead suggest that magnetic confinement and heating must be at work.
