 | | Off-plane Reflection Grating. Geometry for an off-plane reflection grating for the XGS |
Just like NASA’s Chandra X-ray Observatory and the European Space Agency’s XMM-Newton X-ray Observatory, Constellation-X will carry gratings for making high-quality spectral measurements at low X-ray energies.
Gratings are optical devices that intercept X-rays and then disperse them to a detector, similar to a prism. In essence, the gratings sort X-rays into wavelengths, or energies, improving the ability of astronomers to see fine details in a spectrum. And it's the details that reveal the fingerprints of different chemical elements, along with their temperatures and velocities.
Chandra and XMM-Newton use different gratings technologies. But both designs allow astronomers to make detailed measurements of material floating in the vast stretches of space between galaxies, and matter spewing out from the vicinity of black holes. But Chandra and XMM-Newton gratings throw away more than three-fourths of the X-ray photons that strike them. In Chandra's case, for example, X-rays scatter off the gratings’ web-like support structure.
 | | Transmission Grating. Geometry for a transmission grating for the XGS |
To fulfill its scientific objectives, Con-X's gratings will be two to three times more efficient, particularly at lower (softer) X-ray energies. Two grating designs have been proposed, and an open competition will decide which one is developed for the mission. But whichever design wins, the Con-X gratings will provide better spectral resolution and cover a wider range of X-ray energies.
With Con-X's improved gratings and large mirrors, astronomers may solve an enduring mystery: the Universe’s missing atoms. Astronomers have inventoried the amount of familiar matter (made of protons, neutrons, and electrons) locked up in galaxies and intergalactic space. But the total amount is less than half the amount predicted by theories of how much matter formed in the Big Bang.
Observations with Chandra and other observatories suggest that much of the missing atomic matter exists as warm gas floating between galaxies. Thanks to Con-X, astronomers should be able to detect the spectral signature of various elements in this gas, solving this long-standing mystery once and for all.
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