1.5.2 Scientific Objectives

A wide variety of astronomical objects emit X-rays, from stellar atmospheres to hot interstellar gas, galactic halos, and active galaxies. ACIS will enable AXAF to obtain high-resolution images of astronomical objects with simultaneous moderate spectral resolution, high-resolution dispersed spectra of point sources, time-resolved spectra and/or images, and moderate resolution dispersed spectra of extended sources. The spatial and spectral resolution in conjunction with the detector sensitivity and collecting area will allow forefront investigation into many areas of astrophysics. Among the objectives are to:

• measure accurately the discrete X-ray source contribution to the X-ray background
• determine galaxy and galaxy cluster structure and evolution, and substructure of intracluster plasma, out to a redshift of 1-2
• map the temperature and elemental abundance distribution, especially of iron, in clusters of galaxies
• study characteristics of active galactic nuclei, starburst galaxies and quasars, particularly emission mechanisms, time-variability, jets and lenses
• detect and determine the distribution and types of X-ray sources out to the distance of the Virgo cluster
• test Compton models of quasars and active galaxies by studying time variability as a function of energy
• classify emission from normal galaxies out to 800 Mpc and beyond
• determine the abundance of iron in supernova remnants (SNR) to ascertain the composition of the precursor star and verify models of nucleosynthesis
• determine the temperature of neutron stars in SNR to test cooling theories
• detect and identify SNR and Crab-like pulsars out to M31
• measure temperature and emission measure distributions in stellar coronal X-ray sources
• conduct time-resolved spectroscopic studies of accreting compact objects to define the disk geometry
• determine the contribution of stars to the soft X-ray background
• measure the abundance of elements in the interstellar medium
• evaluate the role of X-ray ionization in regulating star formation in molecular clouds
• study the properties and structures of stellar coronae as a function of stellar ages
• determine important physical properties of interstellar dust