The history of Japan Aerospace Exploration Agency (JAXA) in launching x-ray telescopes into space has been marked by challenges and setbacks. The first attempt failed to reach orbit, the second succumbed to an accidental coolant dump, and the third lasted a mere 37 days before encountering a fatal spin that tore apart its spacecraft. However, JAXA’s persistence is about to bear fruit with the upcoming launch of the X-Ray Imaging and Spectroscopy Mission (XRISM) on August 26th.
XRISM is poised to revolutionize x-ray astronomy by providing astronomers with unprecedented insights into the hot gases enveloping phenomena like supernovae, black holes, and galaxy clusters. The instrument is equipped with a groundbreaking device developed by NASA to achieve what has long been a challenge for x-ray telescopes: splitting x-ray wavelengths similar to how a prism separates visible light.
This advanced x-ray spectroscopy will not only enable researchers to observe the properties of hot gases but also to decipher their composition and motion. Dr. Poshak Gandhi, an astrophysicist from the University of Southampton, hails XRISM as a pioneering endeavor, thanks to its innovative detector.
Given that Earth’s atmosphere blocks x-rays, space-based observatories are a necessity to observe them. However, capturing x-ray images in space presents its own set of difficulties. Traditional mirrors fail to reflect x-rays, necessitating the use of nested cylindrical mirrors to redirect and focus the photons.
While this approach allows imaging of the hot gases that constitute a significant portion of visible matter in the universe, astronomers aspire for more. They seek to differentiate between various colors of x-ray light, which standard spectrometers struggle to achieve.
In the 1990s, NASA’s Goddard Space Flight Center developed a chip-based sensor named a microcalorimeter. This sensor can measure the energy of individual x-ray photons, a capability that proved invaluable during the ill-fated Hitomi telescope mission. Hitomi’s brief but transformative observations demonstrated the potential of microcalorimeters.
These sensors register the minuscule amounts of heat generated when an x-ray photon strikes a pixel in the calorimeter, allowing for precise energy measurement. This requires cooling the device to nearly absolute zero temperatures.
Hitomi’s mission offered a glimpse into the microcalorimeter’s potential. It studied the Perseus galaxy cluster, revealing intricate details within the gas’s x-ray emission. These observations unveiled specific elements, like iron, indicating the origins of heavy elements expelled by supernovae. The chemical composition resembled that of the Sun, a surprising finding.
Additionally, Hitomi’s observations challenged existing theories by revealing unexpectedly calm gas motions within the cluster. XRISM aims to build on these discoveries by studying other clusters to establish whether Perseus is unique.
Apart from investigating galaxy clusters, XRISM is primed to explore the x-ray emissions surrounding supernovae remnants and various types of black holes. This includes supermassive black holes at galactic centers and stellar-mass black holes that interact with companion stars. Detecting black holes through x-ray observations is relatively straightforward, but understanding the dynamics of swirling matter and its potential impact on galaxies remains a complex endeavor.
JAXA has taken extensive measures to ensure XRISM’s success, learning from the failures of its predecessors. The telescope features improvements in attitude control, redesigned coolant systems, and a backup mechanical cooler to extend its operational lifespan. Although XRISM has fewer instruments than Hitomi, its spectroscopic capabilities promise to drive cutting-edge research.
The x-ray astronomy community faces challenges with aging flagship missions like NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton. Both telescopes are beyond their initial design lifetimes, grappling with issues like reduced sensitivity and detector aging. As replacements aren’t expected until the mid-2030s at the earliest, XRISM’s successful launch is vital for sustaining progress in the field.
XRISM holds the promise of being the predominant x-ray mission of the 2020s, poised to unravel cosmic mysteries by providing unparalleled insights into the behavior of hot gases, the composition of elements, and the intricate dynamics of phenomena like black holes and supernovae. As the launch date approaches, astronomers and researchers anticipate a new era of x-ray astronomy that could redefine our understanding of the universe’s most enigmatic phenomena.
