The physics of young stellar objects: X-rays, magnetism, and high-energy phenomena

Abstract

The association between star-forming regions and X-rayemission wasdiscovered as soon as X-ray satellites became available, over 30 yearsago. However, understanding of the nature of this association reallystarted when X-ray images and the resulting source identificationcould be obtained. We now know that essentially all young stellarobjects, T Tauri stars and protostars, are X-ray emitters, althoughthe case of the youngest, Class 0 protostars, is less clear. Thepaper briefly reviews X-ray emission and absorption mechanisms, andemphasizes the "solar paradigm" for the interpretation of the X-rayemission, originating in the magnetic activity of young stellarobjects. The possibility of star-disk magnetic interactions inprotostars is also examined. In addition, feedback effects on thecircumstellar disks are presented: ionization, and the associatedcoupling with magnetic fields; particle irradiation, and itsconsequences for the origin of "extinct radioactivities" inmeteorites.