This illustration shows the locations and energy ranges of ASTRO-H science instruments and their associated telescopes. One keV equals 1,000 electron volts, which is hundreds of times the energy of visible light. Credits: JAXA/NASA’s Goddard Space Flight Center
Black hole enthusiasts, galaxy cluster aficionados, and X-ray astronomers have much to be excited about. On Feb. 12, JAXA will be launching their 6th satellite dedicated to X-ray astronomy, ASTRO-H, from the Tanegashima Space Center in Kagoshima, Japan. The observatory carries a state-of-the-art instrument and 2 telescope mirrors built at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. The launch is at 3:45 a.m. EST.
ASTRO-H is expected to provide breakthroughs in a wide variety of high-energy phenomena in the cosmos, ranging from the superheated material on the brink of falling into a black hole to the evolution of galaxy clusters. It has 4 advanced instruments covering a broad energy range, from low-energy, or “soft,” X-rays around 300 electron volts (eV) to soft gamma rays up to 600,000 eV. For comparison, the energy of visible light spans about 2 to 3 eV.
The ASTRO-H spacecraft as it appeared on Nov. 27, 2015, at Tsukuba Space Center in Japan. The open compartment visible at lower left houses the Soft X-ray Spectrometer. Credits: JAXA
“We see X-rays from sources throughout the universe, wherever the particles in matter reach sufficiently high energies,” said Robert Petre, chief of Goddard’s X-ray Astrophysics Lab. “These energies arise in a variety of settings, including stellar explosions, extreme magnetic fields, or strong gravity, and X-rays let us probe aspects of these phenomena that are inaccessible by instruments observing at other wavelengths.” ASTRO-H is capable of observing X-ray sources, like galaxy clusters and neutron stars, more than 10X fainter than its predecessor, Suzaku.
The Goddard team provided identical mirror assemblies for both of the Soft X-ray Telescopes aboard ASTRO-H. Each is 17.7 inches (45 centimeters) across and contains 1,624 precisely aligned aluminum mirror segments arranged in 203 concentric shells. Credits: NASA’s Goddard Space Flight Center
2 identical Soft X-ray Telescopes include mirror assemblies. As X-rays can penetrate matter, the mirrors rely on what scientists refer to as grazing incidence optics. X-ray light skimming the surface of curved mirror segments is deflected toward the telescope’s focal point. One Soft X-ray Telescope focuses light onto an advanced wide-field camera provided by Japan, while the other directs it into the Soft X-ray Spectrometer (SXS). Astronomers typically learn about the composition, temperature and motions of cosmic sources by spreading out the wavelengths of light into a rainbow-like spectrum. But astrophysicists have devised an alternative approach for measuring X-ray “colors,” called microcalorimetry, that produces unprecedented spectral resolution without diluting their intensity as happens in previously employed approaches.
The heart of the ASTRO-H Soft X-ray Spectrometer is the microcalorimeter array at center. The five-millimeter square forms a 36-pixel array. Each pixel is 0.824 millimeter on a side, or about the width of the ball in a ballpoint pen. The detector’s field of view is approximately three arcminutes, or one-tenth the apparent diameter of the full moon. Credits: NASA’s Goddard Space Flight Center
The SXS measures the heat generated when photons, strike the detector. The SXS precisely determines the energy of individual X-ray photons by measuring the small temperature increase made by each one. Because the changes are so small, the detector is cooled to -459.58F—a fraction of a degree above 0K Thanks to a series of nested vacuum containers called dewars, a supply of supercold liquid helium, and a sequence of mechanical and magnetic refrigerators, the SXS is expected to keep its cool for >3yrs. “The technology used in the SXS is leading the way to the next generation of imaging X-ray spectrometers, which will be able to distinguish tens of thousands of X-ray colors while capturing sharp images at the same time,” said aroline Kilbourne, SXS.
The observatory also carries 2 identical Hard X-ray Telescopes and their associated cameras, which image light from 5,000 to 80,000 eV, and 2 Soft Gamma-ray Detectors, sensitive to light from 60,000 to 600,000 eV but do not produce images.
http://www.nasa.gov/feature/goddard/2016/new-x-ray-space-observatory-to-study-black-holes-and-history-of-galaxy-clusters/
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