Led by the Japan Aerospace Exploration Agency (JAXA), Hitomi was launched on Feb. 17. Following the successful activation of the observatory and instruments, Hitomi suffered a mission-ending spacecraft anomaly on March 26.
Before its demise, though, Hitomi was able to peer into the Perseus cluster of galaxies, an assemblage of thousands of galaxies bound together by gravity. Located about 240 million light-years away and named for its host constellation, the Perseus galaxy cluster contains a vast amount of extremely hot gas. At temperatures averaging 90 million degrees Fahrenheit (50 million degrees Celsius), the gas glows brightly in X-rays. Prior to Hitomi's launch, astronomers lacked the capability to measure the detailed dynamics of this gas, particularly its relationship to bubbles of gas expelled by an active supermassive black hole in the cluster's core galaxy, NGC 1275.
For the first time, thanks to Hitomi's revolutionary Soft X-ray Spectrometer (SXS), an instrument developed and built by Goddard scientists working closely with colleagues from several institutions in the United States, Japan, and the Netherlands, astronomers have mapped the motion of X-ray-emitting gas in a cluster of galaxies and shown it moves at cosmically modest speeds.
The total range of gas velocities directed toward or away from Earth within the area observed by Hitomi was found to be about 365,000 miles an hour (590,000 kilometers per hour) -- enormous by human standards but surprisingly modest on cosmic scales. The observed velocity range indicates that turbulence is responsible for only about 4 percent of the total gas pressure. This result is of particular interest to astrophysicists. Turbulent pressure was a previously unmeasured quantity that could significantly impact estimates of the cluster's mass. The SXS measurements show that only minor corrections are needed.
The Perseus observation provides a tantalizing glimpse of the tremendous advance that X-ray microcalorimetry will bring to astrophysics. U.S. researchers pioneered development of the technology in the 1980s, but Hitomi's all-too-brief run represents its most successful space application to date.