  The International X-ray Observatory (IXO), a joint NASA-ESA-JAXA effort, will
address fundamental and timely questions in astrophysics: What happens close to
a black hole? How did supermassive black holes grow? How does large scale
structure form? What is the connection between these processes?
  To address these science questions, IXO will trace orbits close to the event
horizon of black holes, measure black hole spin for several hundred active
galactic nuclei (AGN), use spectroscopy to characterize outflows and the
environment of AGN during their peak activity, search for supermassive black
holes out to redshift z = 10, map bulk motions and turbulence in galaxy
clusters, find the missing baryons in the cosmic web using background quasars,
and observe the process of cosmic feedback where black holes inject energy on
galactic and intergalactic scales.
  IXO will employ optics with 20 times more collecting area at 1 keV than any
previous X-ray observatory. Focal plane instruments will deliver a 100-fold
increase in effective area for high-resolution spectroscopy, deep spectral
imaging over a wide field of view, unprecedented polarimetric sensitivity,
microsecond spectroscopic timing, and high count rate capability. The
improvement of IXO relative to current X-ray missions is equivalent to a
transition from the 200 inch Palomar telescope to a 22m telescope while at the
same time shifting from spectral band imaging to an integral field
spectrograph.
