International X-ray Observatory

The International X-ray Observatory (IXO) is a cancelled X-ray telescope that was to be launched in 2021 as a joint effort by NASA, the European Space Agency (ESA), and the Japan Aerospace Exploration Agency (JAXA). In May 2008, ESA and NASA established a coordination group involving all three agencies, with the intent of exploring a joint mission merging the ongoing XEUS and Constellation-X projects. This proposed the start of a joint study for IXO. NASA was forced to cancel the observatory due to budget constrains in fiscal year 2012. ESA however decided to reboot the mission on its own developing Advanced Telescope for High Energy Astrophysics as a part of Cosmic Vision program. X-ray observations are crucial for understanding the structure and evolution of the stars, galaxies, and the Universe as a whole. X-ray images reveal hot spots in the Universe—regions where particles have been energized or raised to very high temperatures by strong magnetic fields, violent explosions, and intense gravitational forces. X-ray sources in the sky are also associated with the different phases of stellar evolution such as the supernova remnants, neutron stars, and black holes. IXO will explore X-ray Universe and address the following fundamental and timely questions in astrophysics: 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. This will allow astronomers to understand better the history and evolution of matter and energy, visible and dark, as well as their interplay during the formation of the largest structures. Closer to home, IXO observations will constrain the equation of state in neutron stars, black holes spin demographics, when and how elements were created and dispersed into the intergalactic medium, and much more. To achieve these science goals, IXO requires extremely large collecting area combined with good angular resolution in order to offer unmatched sensitivities for the study of the high-z Universe and for high-precision spectroscopy of bright X-ray sources. The large collecting area required because, in astronomy, telescopes gather light and produce images by hunting and counting photons. The number of photons collected puts the limit to our knowledge about the size, energy, or mass of an object detected. More photons collected means better images and better spectra, and therefore offers better possibilities for understanding of cosmic processes.