| emission nebula (ĭ-mĭsh'ən) A nebula that absorbs ionizing ultraviolet radiation from nearby hot stars or star remnants and reemits it as visible light. HII regions, planetary nebulae, and nebulae created by the explosion of supernovae are different kinds of emission nebulae. See more at nebula. |
in astronomy, a bright, diffuse light sometimes associated with supernova remnants or with stars whose temperatures exceed 20,000 K. The excitation process necessary to provide observed optical and radio energies in such gaseous regions was long an astronomical puzzle. Spectral and polarization studies of the 1950s suggested that their luminosity largely results from synchrotron radiation-energy from electrons accelerated in a magnetic field, as seen in certain particle accelerators.