New X-ray Observatory Takes to the Skies

Japan’s newest X-ray satellite, Hitomi (formerly Astro-H), promises to reveal the hot and hidden universe.

Earlier today a H-IIA rocket lit up the skies over Tanegashima, Japan, sending the Japan Aerospace Exploration Agency's new X-ray observatory into orbit. Watch JAXA's video of the launch — countdown begins around 19:00:

Formerly known as NeXT (New X-ray Telescope) and then as Astro-H, Hitomi (meaning "pupil of the eye") now flies high above Earth’s atmosphere, joining six other X-ray space observatories in studying the hot and violent universe. Hitomi’s unique view will help astronomers trace the evolution of galaxy clusters and peer through thick clouds of dust and gas to investigate the growth history of black holes.

Weighing more than 2½ tons and measuring 46 feet in length once its telescope focal boom is extended, Hitomi is the largest astronomical satellite yet lofted by JAXA. Circling at an altitude of 575 kilometers in an orbit very similar orbit to that of the Hubble Space Telescope, Hitomi should be visible from latitudes within 40° of the equator.

More than 250 scientists from 61 countries collaborated to design and build Hitomi. After three months to check and calibrate instruments, it’s expected to achieve a higher resolution at higher X-ray energies than previous missions, measuring X-ray energies from 300 to 600,000 electron volts (0.3 to 600 keV). For comparison, the Chandra X-ray Observatory covers 0.1 to 10 keV and the Nuclear Spectroscopic Telescope Array (NuSTAR) from 3 to 79 keV.

X-ray photons pass right through solid material, but they'll reflect at glancing angles. So X-ray telescopes nest many mirrors inside one another, like the layers of an onion, each one almost parallel to arriving radiation. Hitomi's Soft X-ray Telescope contains 203 concentric shells of aluminum mirror segments.
NASA GSFC

Hitomi sports four types of detectors that will each capture X-ray photons one at a time. Working in the low-energy range (up to 10 keV), the Soft X-ray Imager will image incoming X-rays using a CCD camera, while the Soft X-ray Spectrometer (SXS) measures their energies to unprecedented precision. Developed by NASA, SXS is the first microcalorimeter flown on an observatory-class mission and will offer the highest resolution ever at low-energy X-rays.

The Hard X-ray Imager and Soft Gamma-ray Detector will perform spectroscopy as well, extending the observatory's capability into the high-energy (up to 600 keV) range. Hitomi will record the broadest range of X-ray energy of any observatory.

“It will be the only X-ray observatory to offer both capabilities [seeing both low-energy and high-energy X-rays] at the same time for every observation,” says Laura Brenneman (Harvard-Smithsonian Center for Astrophysics).

The primary mission is slated for three years, though Hitomi will probably operate on an extended mission beyond that. Chandra, for example, is still providing X-ray views of the universe more than 16 years after its launch. And expectations are high: Hitomi should shed light on the dynamic properties of gas accretion disks surrounding black holes, revealing how material behaves near extreme gravitational fields. The observatory will also investigate the source of energetic particles known as cosmic rays, study the behavior of galactic jets, and could even probe the nature of dark matter.

Now safely in orbit, Hitomi is set to revolutionize modern X-ray astronomy.