The Formation and Early Evolution of Stars

The discovery of bright X-ray emission from young low-mass stars in the wake of the launch of the EINSTEINX-ray observatory (see Chap. 2) [66, 67] truly took researchers by surprise. X-rays from Orion had been detected with Uhuru, the first X-ray satellite launched in the early 1970s, but due to the lack of spatial resolving power a connection to young low-mass stars seemed far from likely. At the time, these stars were investigated for their complex emission patterns at long wavelengths. Models for gravitational collapse do not provide many clues about mechanisms for emissions at wavelengths much shorter than a few microns (see Chaps. 4 and 5). High energy emission requires special circumstances and the responsible physical processes are often different from the ones at the origins of the optical and IR emissions. In order to emit at short wavelengths, one either needs very high temperatures or very high magnetic field strengths or some mechanism to produce high-velocity electrons. The previous chapters already demonstrated that gravitational potentials in protostellar systems are by far too small to free enough energy (see Sect. 6.7). Thus the energy has to come from a different pool, which is most likely rotational and magnetic energy inherited from pre-collapse cloud dynamics. Synchrotron radiation from magnetic fields as high as 10¹¹G can be ruled out on the grounds that superdense degenerate matter, as found in neutron stars, is needed to carry such high field densities [840]. Chapters 6 and 8 also showed that magnetic field strengths in protostellar environments do not exceed 1 or a few kG.