Constellation-X Science

The Constellation-X science objectives are achievable as a result of ongoing instrumentation (optics and detectors) development that promises the next quantum leap in capability. High resolution X-ray spectra from the Chandra and XMM-Newton grating spectrometers are reaching the level of detail previously obtained in the optical band, demonstrating the power of X-ray spectroscopy but limited by throughput to only a small number of bright X-ray sources. The 0.3 - 10 keV X-ray band contains the inner (K-shell) lines for all of the abundant metals from carbon to zinc as well as many L-shell lines. These atomic transitions provide plasma diagnostics that enable precise characterization of physical conditions in sources. A spectral resolving power of at least 300 is required to separate the density and temperature-sensitive triplet lines of helium-like ions of O, Si and S. In the spectral region between 6 and 7 keV that covers the Fe K complex a resolving power of order 2000 is required to resolve the complex Fe K structure arising in the accretion disks of black holes. Resolving powers of 300-3000 provide absolute velocity measurements ranging from 100-1000 km/s which are found in many astronomical systems.

The throughput of Constellation-X (more than 100 times the throughput of the Chandra and XMM high resolution grating spectrometers across the 0.6-10 keV band) along with its high spectral resolution are essential for achieving four primary science objectives described here:

Black Holes: Using black holes to test General Relativity (GR) and measuring black hole spin
Dark Energy: Improving the constraints on the key Dark Energy (DE) parameters by a factor of ten
Missing Baryons: Unambiguous detection of the hot phase of the Warm-Hot Intergalactic Medium (WHIM) at z>0
Neutron Star Equation of State: Measuring the mass-radius relation of neutron stars to determine the Equation of State (EOS) of ultra-dense matter

In addition, the large increase in capabilities provided by the Constellation X-ray observatory will enable major advances covering all of astrophysics from solar system objects to distant quasars. These science topics are enabled by the mission, but do not create any additional drivers on the performance of the observatory. Two of these, Evolution of Supermassive Black Holes and Cosmic Feedback are discussed, along with a subset of other science topics, in the Observatory Science sections.