X-Raying the Universe

Illustration of the black hole in the NGC 4151 galaxy

 

XRISM, an X-ray telescope designed to facilitate discoveries about the evolution of galaxy clusters and the extreme space-time around black holes, was launched into space in September 2023. Prof. Ehud Behar of the Technion Faculty of Physics, an expert on X-ray observations from space, is part of the XRISM mission’s core science team. His team, which includes Technion PhD students, has been leading the analysis of several key XRISM observations in its first year of operation.

In September, a media briefing was held in Japan about the mission’s main achievements:
• Discovery of the 3D structure of the N132D supernova remnant in the Large Magellanic Cloud, a satellite galaxy of our Milky Way, and detection of iron at very high temperatures. The remnants, created by an explosion that occurred about 3,000 years ago, provide an unprecedented window into the lives and deaths of massive stars. XRISM’s observation revealed that – contrary to the prevailing hypothesis that the remnants of N132D are spherical – they actually have a tubular (or donut) shape, expanding at a speed of 1,200 kilometers per second. The supernova explosion produced iron, and the resulting shock waves heated it to extremely high temperatures – around 10 billion degrees Celsius.

• Discovery of the structure surrounding the supermassive black hole in the NGC 4151 galaxy, located about 62 million light-years away from us. XRISM’s observations provide unprecedented insights into the material surrounding the black hole at the center of the galaxy, which has a mass 30 million times that of the Sun. Specifically, the observations show the reflection of X-rays from gas in the accretion disk around the black hole, which spins at speeds of up to 15,000 km/s. These discoveries offer new information about the growth of black holes influenced by the surrounding material.

Analysis of data on the black hole NGC 4151 (Photo: Japanese Space Agency, European Space Agency)

XRISM has two primary scientific instruments: Resolve, a high-resolution spectrometer that can measure the energy (color) of X-ray photons to unprecedented precision; and Xtend, an X-ray imaging camera. According to the XRISM website, “At first glance, the Universe seems barren, a place cold, dark, and empty. But the Universe as revealed in X-rays — faint thought they are — paints a different picture. Hot plasmas at millions of degrees. Jets emanating from black holes. Ultra-high energy particles traveling at speeds surpassing 99% of the speed of light.”

The Resolve spectrometer makes precise measurements of the “color” of X-rays, a capability that makes it the primary instrument of the XRISM mission. “The fireworks that decorate the summer skies come about when different chemical elements are made to glow hot. Each metal responds to heating by emitting its own distinctive color.”
Using Resolve, the scientific community can map the elements in our Universe and, based on these data, discover a wide variety of facts in three main domains: (1) the kinematic “blueprint” for galaxy clusters, the largest structures in the Universe; (2) the “recipe for producing chemical elements in the Universe”; and (3) “the edge of space-time around black holes.” by studying matter just before it falls into black holes, or is ejected at enormous speeds away from it.”

According to Prof. Behar, “The Resolve spectrometer is a technological revolution. Its sensor is made of superconducting pixels that are kept at a low temperature. Every X-ray photon that hits a pixel raises the temperature and changes its electrical properties, enabling the system to measure the photon’s energy with unprecedented precision. Resolve has been operating in space for a year now, giving us a new wealth of information about the astrophysical sources the telescope is observing. It helps us map important phenomena in the universe and, based on our observations of them, understand dynamic processes related to the formation of elements and the evolution of cosmic structures. This is a very exciting project, and we are inundated with new data coming to us daily from space via XRISM.”

XRISM is a joint project of the Japan Aerospace Exploration Agency (JAXA) and NASA, with contributions from the European Space Agency (ESA). Prof. Behar is the only researcher on the telescope’s science team who is not from any of the countries in which these entities are located. He was personally appointed by the director of the Japan Aerospace Exploration Agency. XRISM’s design incorporates lessons learned from previous Japanese telescopes decommissioned at various stages due to malfunctions. The XRISM mission aims to ensure continuity in X-ray observations — a continuity that could have been disrupted by the time gap between previous X-ray telescopes and the ATHENA telescope, which is not expected to be launched before 2035. XRISM will be the only telescope of its kind for at least the next 13 years. This will ensure the observational continuity required for expanding our understanding of astrophysical phenomena.