JAXA Japan Aerospace Exploration Agency

The Japan Aerospace Exploration Agency (JAXA) hereby announces that a paper presenting the results of research based on X-Ray Imaging and Spectroscopy Mission (XRISM) was published in the UK scientific journal "Nature" on February 13, 2025(JST).

Title:

The Bulk Motion of Gas in the Core of the Centaurus Galaxy Cluster

Journal:

Nature

DOI:

10.1038/s41586-024-08561-zExternal Link

The Bulk Motion of Gas in the Core of the Centaurus Galaxy Cluster

1. Key Points

•

Superior capabilities of the X-ray spectrometer onboard XRISM enabled the detection of the presence of oscillating hot gas motion, for the first time in the world, in the center of the Centaurus Cluster.(figure 1)

•

The observed gas motion provides direct evidence of collisions and mergers between galaxy clusters.

•

Direct measurement of the velocity structure of the gas helps elucidate the heating mechanism in the cluster core, which has been a mystery for the past few decades.

2. Abstract

The Universe evolves under the influence of gravity. Galaxies, vast collections of stars and interstellar medium, form larger structures known as galaxy clusters-colossal cosmic assemblies bound together by the gravitational pull of dark matter. Within these clusters, gas trapped by intense gravitational forces is heated to tens of millions of degrees Kelvin, emitting powerful X-rays. Astronomers have long believed that galaxy clusters continue to grow through repeated collisions and mergers, but direct observational evidence has been elusive until now. In a groundbreaking study, XRISM has, for the first time, captured definitive proof of this dynamic process at the core of a galaxy cluster.
The central regions of galaxy clusters are among the brightest X-ray sources in the Universe. Theoretically, the loss of energy from their intense radiation should cause the surrounding gas to cool over time —a phenomenon known as radiative cooling. However, observations have revealed that the gas remains unexpectedly hot, leaving scientists puzzled. One leading hypothesis suggested that gas motion could play a key role in maintaining these high temperatures, yet previous instruments lacked the precision to confirm this.
An international research team (XRISM Collaboration, hereinafter referred to as the “research team”) has precisely measured the velocity structure of hot gas in a galaxy cluster’s core. Their findings reveal that gas motion aligns with oscillations ("sloshing") triggered by collisions and mergers between clusters. These oscillations stir the hot gas, preventing excessive cooling and maintaining its high temperature.
This discovery marks a significant leap forward in our understanding of galaxy formation, cluster evolution, and the large-scale structure of the Universe by uncovering new details about gas dynamics with unprecedented precision.

Figure 1：

Illustration of the center of the Centaurus Cluster drawn based on XRISM observations and other observations. The bluish color indicates high-temperature gas. The white indicates galaxies, and the reddish brown indicates low-temperature gas.

3．Main Text

How did the Universe evolve into its current structure after the Big Bang? This fundamental question has driven decades of astronomical research. The Universe is filled with vast cosmic structures. The Solar System is a collection of planets and small Solar System bodies orbiting the Sun, while a galaxy is a vast assembly of stars bound by gravity. However, these structures did not exist from the Universe’s beginning; they gradually formed and grew under the influence of gravity acting on matter. Violent cosmic events, such as collisions and mergers between celestial bodies, shaped our current universe.
The largest known structures formed through this cosmic evolution are galaxy clusters. These immense conglomerations of galaxies are held together by the powerful gravitational pull of dark matter, an invisible and mysterious substance that makes up most of the Universe's mass. However, the dark matter and galaxies alone are not the dominant components of these clusters—significant mass exists in the form of gas, composed of hydrogen and helium gas left over from the Big Bang. As this primordial gas falls into a galaxy cluster, the immense gravitational energy converts it into superheated gas at temperatures of tens of millions of degrees. At such extreme temperatures, the gas emits X-rays, making X-ray observations essential for studying the evolution and dynamics of galaxy clusters. The mass of this hot gas is significantly greater than that of the galaxies themselves, meaning that understanding galaxy clusters requires understanding this high-energy component.
One of the great astrophysical puzzles has been why the hot gas in the center of a galaxy cluster does not cool over time. Theoretically, the gas should gradually lose energy through X-ray emission, cooling down in a process known as radiative cooling. However, previous observations have shown that, contrary to expectations, the gas remains persistently hot. This discrepancy suggests an unknown heating mechanism is at work, preventing the hot gas from cooling as expected. Unraveling this mystery is crucial for understanding the formation and evolution of the Universe's largest structures.
From December 2023 to January 2024, the research team used XRISM to observe the nearby galaxy cluster, the Centaurus Cluster, located approximately 100 million light-years from Earth. The goal was to investigate the motion of the hot gas in the core of the galaxy cluster.
Figure 2 displays the X-ray spectrum of the cluster’s center, captured by Resolve, the cutting-edge soft X-ray spectrometer onboard XRISM. By analyzing this spectrum, the research team aimed to gain deeper insights into how gas moves within the cluster. Precise spectroscopic measurements of emission lines—the sharp, spike-like features in Figure 2—are essential to study this motion. Resolve achieves an energy resolution about 30 times higher than conventional instruments, making it particularly adept at measuring gas velocity with unprecedented accuracy.
Observations revealed that the hot gas at the center of the Centaurus Cluster flows toward Earth at speeds of 130 to 310 km per second (Figure 3). This oscillating ("sloshing") motion is believed to stir the surrounding hot gas, preventing it from cooling and maintaining the high temperatures observed in the cluster’s core.

Figure 2：

X-ray spectrum of the central region of the Centaurus Cluster taken by Resolve onboard XRISM. In the background is an image of the same area acquired by the Chandra X-ray Observatory.

Figure 3：

Explanation of the high-temperature gas flow derived from XRISM observations. The galaxy NGC 4696 is located at the center of the Centaurus cluster of galaxies.

The research team compared XRISM’s observations with numerical simulations and concluded that past collisions and mergers of clusters are responsible for the observed hot gas sloshing. Figure 4 illustrates this mechanism: the Centaurus Cluster has undergone multiple interactions with smaller clusters, and the hot gas in its core is still sloshing due to these past collisions. XRISM’s observations reveal that these motions stir the gas, preventing it from cooling and maintaining the cluster’s high central temperature.

Figure 4：

Illustration showing the mechanism of the sloshing motion of high-temperature gas in the center of a galaxy cluster.

This research has unveiled the gas motions within a galaxy cluster with unprecedented precision. XRISM's observations provide direct evidence of how clusters evolve through collisions and mergers, offering a crucial missing piece in our understanding of cosmic history. By capturing the velocity of hot gas in such detail, this study marks a major leap forward in our knowledge of large-scale cosmic evolution. The discovery of these dynamic gas velocities not only deepens our insight into galaxy clusters but also holds the potential to greatly advance our understanding of the formation and evolution of other celestial bodies in the Universe.

4. Publication Information

Journal：

Nature

Title：

The Bulk Motion of Gas in the Core of the Centaurus Galaxy Cluster

Authors：

XRISM Collaboration

Marc Audard¹, Hisamitsu Awaki², Ralf Ballhausen^3,4,5, Aya Bamba⁶, Ehud Behar⁷, Rozenn Boissay-Malaquin^4,5,8, Laura Brenneman⁹, Gregory V. Brown¹⁰, Lia Corrales¹¹, Elisa Costantini¹², Renata Cumbee⁴, María Díaz Trigo¹³, Chris Done¹⁴, Tadayasu Dotan¹⁵, Ken Ebisawa¹⁵, Megan E. Eckart¹⁰, Dominique Eckert¹, Teruaki Enoto¹⁶, Satoshi Eguchi¹⁷, Yuichiro Ezoe¹⁸, Adam Foster⁹, Ryuichi Fujimoto¹⁵, Yutaka Fujita*¹⁸, Yasushi Fukazawa¹⁹, Kotaro Fukushima¹⁵, Akihiro Furuzawa²⁰, Luigi Gallo²¹, Javier A. García^4,22, Liyi Gu¹², Matteo Guainazzi²³, Kouichi Hagino⁶, Kenji Hamaguchi^4,5,8, Isamu Hatsukade²⁴, Katsuhiro Hayashi1⁵, Takayuki Hayashi^4,5,8, Natalie Hell¹⁰, Edmund Hodges-Kluck⁴, Ann Hornschemeier⁴, Yuto Ichinohe²⁵, Manabu Ishida1⁵, Kumi Ishikawa1⁸, Yoshitaka Ishisaki1⁸, Jelle Kaastra^12,26, Timothy Kallman⁴, Erin Kara²⁷, Satoru Katsuda²⁸, Yoshiaki Kanemaru¹⁵, Richard Kelley⁴, Caroline Kilbourne⁴, Shunji Kitamoto²⁹, Shogo Kobayashi³⁰, Takayoshi Kohmura³¹, Aya Kubota³², Maurice Leutenegger⁴, Michael Loewenstein^3,4,5, Yoshitomo Maeda¹⁵, Maxim Markevitch⁴, Hironori Matsumoto³³, Kyoko Matsushita³⁰, Dan McCammon³⁴, Brian McNamara³⁵, François Mernier^3,4,5, Eric D. Miller²⁷, Jon M. Miller¹¹, Ikuyuki Mitsuishi³⁶, Misaki Mizumoto³⁷, Tsunefumi Mizuno³⁸, Koji Mori²⁴, Koji Mukai^4,5,8, Hiroshi Murakami³⁹, Richard Mushotzky³, Hiroshi Nakajima⁴⁰, Kazuhiro Nakazawa³⁶, Jan-Uwe Ness⁴¹, Kumiko Nobukawa⁴², Masayoshi Nobukawa⁴³, Hirofumi Noda⁴⁴, Hirokazu Odaka³³, Shoji Ogawa¹⁵, Anna Ogorzalek^3,4,5, Takashi Okajima⁴, Naomi Ota⁴⁵, Stephane Paltani¹, Robert Petre⁴, Paul Plucinsky⁹, Frederick Scott Porter⁴, Katja Pottschmidt^4,5,8, Kosuke Sato*^28,46, Toshiki Sato⁴⁷, Makoto Sawada²⁹, Hiromi Seta¹⁸, Megumi Shidatsu², Aurora Simionescu¹², Randall Smith⁹, Hiromasa Suzuki¹⁵, Andrew Szymkowiak⁴⁸, Hiromitsu Takahashi¹⁹, Mai Takeo²⁸, Toru Tamagawa²⁵, Keisuke Tamura^4,5,8, Takaaki Tanaka⁴⁹, Atsushi Tanimoto⁵⁰, Makoto Tashiro^15,28, Yukikatsu Terada^15,28, Yuichi Terashima², Yohko Tsuboi⁵¹, Masahiro Tsujimoto¹⁵, Hiroshi Tsunemi³³, Takeshi G. Tsuru¹⁶, Hiroyuki Uchida¹⁶, Nagomi Uchida¹⁵, Yuusuke Uchida³¹, Hideki Uchiyama⁵², Yoshihiro Ueda⁵³, Shinichiro Uno5⁴, Jacco Vink⁵⁵, Shin Watanabe¹⁵, Brian J. Williams⁴, Satoshi Yamada⁵⁶, Shinya Yamada²⁹, Hiroya Yamaguchi¹⁵, Kazutaka Yamaoka³⁶, Noriko Y. Yamasaki¹⁵, Makoto Yamauchi²⁴, Shigeo Yamauchi⁴⁵, Tahir Yaqoob^4,5,8, Tomokage Yoneyama⁵¹, Tessei Yoshida¹⁵, Mihoko Yukita^4,57, Irina Zhuravleva⁵⁸, Marie Kondo²⁸, orbert Werner⁵⁹, Tomáš Plšek⁵⁹, Ming Sun⁶⁰, Kokoro Hosogi⁶⁰, Anwesh Majumder^12,61

¹Department of Astronomy, University of Geneva, Geneva, Switzerland
²Department of Physics, Ehime University, Matsuyama, Japan
³Department of Astronomy, University of Maryland, College Park, MD, USA
⁴NASA / Goddard Space Flight Center, Greenbelt, MD, USA
⁵Center for Research and Exploration in Space Science and Technology, NASA / GSFC (CRESST II), Greenbelt, MD, USA
⁶Department of Physics, University of Tokyo, Tokyo, Japan
⁷Department of Physics, Technion, Haifa, Israel
⁸Center for Space Science and Technology, University of Maryland, Baltimore County, Baltimore, MD, USA
⁹Center for Astrophysics | Harvard-Smithsonian, Cambridge, MA, USA
¹⁰Lawrence Livermore National Laboratory, Livermore, CA, USA
¹¹Department of Astronomy, University of Michigan, Ann Arbor, MI, USA
¹²SRON Netherlands Institute for Space Research, Leiden, The Netherlands
¹³ESO Supernova, Garching bei München, Germany
¹⁴Centre for Extragalactic Astronomy, Department of Physics, University of Durham, Durham, DH1 3LE, UK
¹⁵Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), Kanagawa, Japan
¹⁶Department of Physics, Kyoto University, Kyoto, Japan
¹⁷Department of Economics, Kumamoto Gakuen University, Kumamoto, Japan
¹⁸Department of Physics, Tokyo Metropolitan University, Tokyo, Japan
¹⁹Department of Physics, Hiroshima University, Hiroshima, Japan
²⁰Department of Physics, Fujita Health University, Toyoake, Japan
²¹Department of Astronomy and Physics, Saint Mary’s University, Halifax Nova Scotia, Canada
²²Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA, USA
²³European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Noordwijk, The Netherlands
²⁴Faculty of Engineering, University of Miyazaki, Miyazaki, Japan
²⁵RIKEN Nishina Center, Saitama, Japan
²⁶Leiden Observatory, University of Leiden, The Netherlands
²⁷Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA, USA
²⁸Department of Physics, Saitama University, Saitama, Japan
²⁹Department of Physics, Rikkyo University, Tokyo, Japan
³⁰Faculty of Physics, Tokyo University of Science, Tokyo, Japan
³¹Faculty of Science and Technology, Tokyo University of Science, Chiba, Japan
³²Department of Electronic Information Systems, Shibaura Institute of Technology, Saitama, Japan
³³Department of Earth and Space Science, Osaka University, Osaka, Japan
³⁴Department of Physics, University of Wisconsin, Madison, WI, USA
³⁵Department of Physics and Astronomy, Waterloo Centre for Astrophysics, University of Waterloo, Waterloo Ontario, Canada
³⁶Department of Physics, Nagoya University, Nagoya, Japan
³⁷cience Research Education Unit, University of Teacher Education Fukuoka, Munakata, Japan
³⁸Hiroshima Astrophysical Science Center, Hiroshima University, Hiroshima, Japan
³⁹Department of Data Science, Tohoku Gakuin University, Sendai, Japan
⁴⁰College of Science and Engineering, Kanto Gakuin University, Yokohama, Japan
⁴¹European Space Agency (ESA), European Space Astronomy Centre (ESAC), Madrid, Spain
⁴²Department of Science, Faculty of Science and Engineering, KINDAI University, Osaka, Japan
⁴³Department of Teacher Training and School Education, Nara University of Education, Nara, Japan
⁴⁴Astronomical Institute, Tohoku University, Sendai, Japan
⁴⁵Department of Physics, Nara Women’s University, Nara, Japan
⁴⁶International Center for Quantum-field Measurement Systems for Studies of the Universe and Particles (QUP) / High Energy Accelerator Research Organization (KEK), Tsukuba, Japan
⁴⁷School of Science and Technology, Meiji University, Kawasaki, Japan
⁴⁸Yale Center for Astronomy and Astrophysics, Yale University, New Haven, CT, USA
⁴⁹Department of Physics, Konan University, Kobe, Japan
⁵⁰Graduate School of Science and Engineering, Kagoshima University, Kagoshima, Japan
⁵¹Department of Physics, Chuo University, Tokyo, Japan
⁵²Faculty of Education, Shizuoka University, Shizuoka, Japan
⁵³Department of Astronomy, Kyoto University, Kyoto, Japan
⁵⁴Nihon Fukushi University, Shizuoka, Japan
⁵⁵Anton Pannekoek Institute, University of Amsterdam, Amsterdam, The Netherlands
⁵⁶RIKEN Cluster for Pioneering Research, Saitama, Japan
⁵⁷Johns Hopkins University, Baltimore, MD, USA
⁵⁸Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL, USA
⁵⁹Department of Theoretical Physics and Astrophysics, Faculty of Science, Masaryk University, Brno, Czech Republic
⁶⁰Department of Physics and Astronomy, University of Alabama in Huntsville, Huntsville, AL, USA
⁶¹Astronomical Institute ‘Anton Pannekoek’, University of Amsterdam, Amsterdam, The Netherlands
*Corresponding Authors

DOI：10.1038/s41586-024-08561-zExternal Link

JAXA Japan Aerospace Exploration Agency

Press Release

Study Based on Observation Data from X-Ray Imaging and Spectroscopy Mission (XRISM) Published in Nature

The Bulk Motion of Gas in the Core of the Centaurus Galaxy Cluster

1. Key Points

2. Abstract

3．Main Text

4. Publication Information

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