X-ray Spectroscopy in Astronomy

X-ray Spectroscopy of astronomical sources has made substantial progress in the last five and half decades since the birth of X-ray Astronomy. This is remarkable considering that X-ray astronomy covers nearly three decades of bandwidth in X-ray energies (0.1 - 100 keV) or wavelengths (100 Angstroms to 0.1 Angstroms) , as compared to a very narrow band in the highly advanced field of optical astronomy which is however limited to just an octave of bandwidth.  X-rays from extra-solar sources in the sky come from a bewildering variety of objects: from stars (old and young), exploding stars producing massive shock waves (novae, supernovae), remnants of supernova explosions that leave hot and chemically enriched gas in the interstellar medium of galaxies, extremely hot gas trapped in the deep and large gravitational potential wells of clusters of galaxies, interacting binary systems containing both non-degenerate and degenerate (white dwarfs, neutron) stars and black holes in our galaxy, the super-massive black holes in centres of some galaxies, and highly accelerated (relativistic) particles gyrating around magnetic fields in jets of emissions which also boost the energies of low energy infrared to UV photons to extremely high energies via inverse Compton effect.  It is through X-ray spectroscopy that we identify the emission processes and the conditions leading to those emission processes, and derive the density, temperature, chemical composition, magnetic fields, turbulence etc of the X-ray emitting regions in these sources.  After a brief introduction, I will provide examples of X-ray spectra from various types of sources, and the the kind of information gleaned through spectroscopy (of low and high resolution),  
and where it is headed in future.