X-rays also come from acceleration of particles in outer parts
of a star's atmosphere or corona. Our Sun is a bright source of X-rays. X-rays
are also produced in distant galaxies or Quasars where it it thought that a very
massive black hole (billion times more massive than our Sun) is accreting matter
in the center.
No X-rays from space can get through the Earth's atmosphere to
the ground, so all X-ray astronomy is carried out with instruments on rockets or