The International X-ray Observatory (IXO) is a new X-ray telescope with joint participation from NASA, the European Space Agency (ESA), and Japan's Aerospace Exploration Agency (JAXA). This project supersedes both NASA's Constellation-X and ESA's XEUS mission concepts.

In mid-2008, a officials from ESA, NASA, and JAXA headquarters agreed to conduct a joint study of IXO with a single merged set of top-level science goals. This agreement established key science measurement requirements. The spacecraft configuration for the IXO study is a mission featuring a single large X-ray mirror and an extendible optical bench, with a focal length of 20 m, and a suite of 6 focal plane instruments.

The instruments under study for the IXO concept include: a wide field X-ray imaging detector, a high-spectral-resolution imaging X-ray spectrometer (calorimeter), a hard X-ray imaging detector, an X-ray grating spectrometer, high timing resolution spectrometer, and an X-ray polarimeter. The IXO mission concept will submitted to the U.S. Decadal Process and ESA's Cosmic Vision Plan.

With IXO's high-throughput, scientists will be able to study the high-energy Universe in more detail than ever before. The science objectives of IXO include:

Black Holes and Matter Under Extreme Conditions

• How do supermassive black holes grow? Does this change over cosmic time?
• What are the demographics of black hole spin, and what do they tell us about black hole formation and growth?
• How do black holes generate energy and what is the structure of space-time near the event horizon?
• What is the equation of state of matter in neutron stars?

Formation and Evolution of Galaxies, Clusters, and Large Scale Structure

• How does galaxy cluster evolution constrain the nature of dark matter and dark energy?
• How does cosmic feedback work and influence galaxy formation?
• Where are the missing baryons and do they form a cosmic web in the nearby Universe?

Life Cycles of Matter and Energy

• When and how were the elements created and dispersed?
• How are particles accelerated to extreme energies producing shocks, jets and cosmic rays?
• How do high energy processes affect planetary formation and habitability?
• How do magnetic fields shape stellar exteriors and the surrounding environment?
• What does the Cosmic Web of hot baryons tell us about structure formation and chemical evolution?

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IXO will be a satellite observatory that will launch on either an Atlas V or Arianne V rocket to an orbit around the Sun-Earth L2 point, 1.5 million km away.

Optics

The heart of the mission is the lightweight X-ray optical system. Achieving the 3 square meter collecting area with 5" angular resolution is the main technology driver. The IXO optics will consist of nested grazing-incidence mirrors to focus X-ray photons onto a detector plane. Two independent approaches to achieving the 5" resolution - slumped glass and silicon pore optics - are clear and achievable in the near-future.

Instrumentation

Behind the optics, the IXO instrument suite includes a wide field X-ray imaging detector, a high-spectral-resolution imaging X-ray spectrometer (calorimeter), an X-ray grating spectrometer, high timing resolution spectrometer, and an X-ray polarimeter.

The focal plane instruments will deliver up to 100-fold increase in effective area for high resolution spectroscopy from 0.3–10 keV, deep spectral imaging from 0.2–40 keV over a wide field of view, unprecedented polarimetric sensitivity, and microsecond spectroscopic timing with high count rate capability.

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IXO is being developed by an international collaboration that includes members appointed by ESA, JAXA, and NASA.

Advisory Groups

Several key advisory groups of scientists and engineers are guiding the IXO development. A coordination group oversees the work of the science definition team, the telescope working group, and the instrument working group.

IXO Supporters

In addition to these advisory groups, more than 200 scientists from over 60 institutions around the world are actively involved with IXO. Interested scientists can keep up to date on IXO developments by signing up for the 'ixo-supporters' email list.

The IXO supporters provide help and input to the advisory groups listed above. Many of these supporters are members of previous Constellation-X and XEUS science and instrumentation teams.

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Launch

IXO is currently planned for launch in 2020-2021. Studies to determine the launch vehicle, either the Ariane V or Atlas V rockets, are currently underway.

Science Operations

IXO will be designed to operate for a minimum of 5 years, with a goal of 10 years, so IXO science operations are anticipated to last from 2020 to 2030.

Decadal Survey/Cosmic Visions

During 2009, the IXO mission team is focusing on providing input to the National Research Council's Astronomy and Astrophysics Decadal Survey committee (Astro2010) and the ESA Cosmic Vision process. Note that Constellation-X was ranked as the second space-based priority behind JWST in the 2000 Decadal Survey, and XEUS was selected as a finalist in ESA's Cosmic Vision 2015-2025.