Invisible to our eyes, X-rays emitted by the hot gas that fills much of the Universe can shed light on many cosmic mysteries. The first observations of this gas by JAXA’s X-ray Imaging and Spectroscopy Mission (XRISM) are ready and demonstrate that the mission will play a major role in revealing the evolution of the Universe and the structure of spacetime.
The Japanese-led X-ray Imaging and Spectroscopy Mission (XRISM) observatory has released its first data – a snapshot of a cluster of hundreds of galaxies and a spectrum of star debris in a nearby galaxy, giving scientists a detailed understanding of its chemical composition. XRISM (pronounced “crism”) is led by JAXA (Japan Aerospace Exploration Agency) in collaboration with NASA, and also with participation from ESA (European Space Agency). It was launched on September 6, 2023.
Richard Kelly, XRISM principal investigator at NASA’s Goddard Space Flight Center in Greenbelt, Maryland: “We’ll not only see X-ray images of these sources, but we’ll also study their composition, motion and physical state.” XRISM is designed to detect X-rays with energies up to 12,000 electron volts and will study the hottest regions of the Universe, the largest structures and objects with the strongest gravity. By comparison, the energy of visible light is 2 to 3 electron volts.
The first XRISM test images show a galaxy cluster and a supernova remnant – the shell left behind after the explosion of a massive star. Moreover, XRISM measured the energy of the X-rays emanating from the supernova remnant to reveal the chemical elements it contained. The observations demonstrate the exceptional capabilities of XRISM’s two scientific instruments.
Resolve is a microcalorimeter spectrometer developed by NASA and JAXA. It operates at temperatures just a fraction of a degree above absolute zero inside a refrigerator-sized container of liquid helium. When X-rays hit Resolve’s 6-by-6-pixel detector, they heat the device by an amount corresponding to its energy. By measuring the energy of each individual X-ray, the instrument provides previously unavailable information about the source.
The mission team used Resolve to study N132D, a supernova remnant and one of the brightest X-ray sources in the Large Magellanic Cloud, a dwarf galaxy about 160,000 light-years away in the southern constellation Dorado. The expanding debris is estimated to be about 3,000 years old. They were formed when a star with about 15 times the mass of the Sun ran out of fuel and exploded.
The resolution spectrum shows peaks associated with silicon, sulfur, calcium, argon and iron. These are the most detailed X-ray spectra of an object ever obtained. “These elements formed in the original star and then exploded in a supernova,” said Brian Williams, NASA’s XRISM project scientist at Goddard. “The equipment will allow us to see the shape of these lines in a way that was not possible before, allowing us to determine not only the content of the various elements present, but also their temperature, density and directions of movement with an unprecedented level of accuracy. From there we can piece together information about the original star and the explosion.”
The second XRISM instrument, Xtend, is an X-ray scanner developed by JAXA. This gives XRISM a larger field of view, allowing it to observe an area approximately 60% larger than the average apparent size of the full Moon. Xtend captured an X-ray image of Abell 2319, a massive galaxy cluster located about 770 million light-years away in the northern constellation Cygnus. It is the fifth brightest X-ray cluster in the sky and is currently undergoing a major merger.
The cluster is 3 million light-years in diameter and highlights Xtend’s extensive analysis capabilities. This groundbreaking image is a sweeping view of a nearby galaxy cluster called Abell 2319. In violet, we see X-ray light from million-degree gas that filters between galaxies in the cluster. Observing this gas helps astronomers measure the total mass of a galaxy cluster, revealing information about the birth and evolution of the universe.
“Even before the commissioning process was completed, Resolve was already exceeding our expectations,” said Lillian Reichenthal, NASA XRISM project manager at Goddard. “Our goal was to achieve a spectral resolution of 7 electron volts with the instrument, but now that it is in orbit we are reaching 5. This means we will get even more detailed chemical maps with every spectrum obtained by XRISM.”
Resolve works exceptionally well and is already producing exciting science, despite the problem with the aperture door covering the detector. A door designed to protect the detector before startup failed to open as planned after several attempts, blocking low-energy X-rays, effectively stopping operation at 1,700 electron volts, down from the intended 300.
The commissioning phase of the ship will be completed by the end of January. In February, JAXA will begin calibrating the instruments and demonstrating their capabilities. The time allocated by ESA as part of a public observing program open to scientists around the world will enable European scientists to take advantage of the exceptional scientific opportunities offered by Resolve’s unprecedented high-resolution spectroscopic capabilities. Scientists have already been invited to submit proposals for observations they would like to make starting in August 2024. The deadline is April 4, 2024.
“These first light images demonstrate that XRISM is delivering on its promise to usher in a new era in high-resolution hot gas imaging spectroscopy in the Universe,” says ESA XRISM project scientist Matteo Guainazzi. “I warmly encourage scientists in ESA Member States to take advantage of the unique capabilities offered by XRISM and submit proposals for observations with this magnificent telescope.”
The observations made with XRISM will complement data from ESA’s XMM-Newton X-ray telescope and provide an excellent basis for studies planned by ESA’s future NewAthena large-class mission. The latter is designed to significantly surpass the existing spectroscopic and survey X-ray observatories in scientific capabilities.