An international research group using the X-ray astronomy satellite "XRISM" has announced that galactic winds ejected from massive black holes at galactic centers are not as smooth as previously thought but are emitted intermittently like bullets. They confirmed this by observing the black hole "PDS456" located 2 billion light-years from Earth. Their findings revealed that the wind's energy is greater than expected, forcing a reconsideration of theories about the relationship between galaxies and massive black holes.
Provided by JAXA
Black holes are ultra-high-density celestial objects with extremely strong gravity. The surrounding spacetime is warped, preventing even light from escaping. They form when heavy stars undergo massive explosions at the end of their lives, and massive black holes with masses exceeding one million times that of the Sun exist at the centers of many galaxies. High-speed gas ejected from these holes appears to be deeply involved in the black hole's own growth and star formation within galaxies, but detailed mechanisms remained mysterious due to the lack of high-precision observations.
The research group made use of XRISM, which has been operational since September 2023, to conduct detailed observations of PDS456 in the constellation Serpens in March of last year. By analyzing how surrounding X-rays were absorbed by the gas, they discovered winds consisting of five different velocity components. Previous observations suggested the wind was a single, smooth phenomenon, but the high-precision XRISM captured it as having a "bullet-like, choppy structure." Additionally, based on the wavelengths of light emitted by gas illuminated by X-rays, they found that the wind is ejected in nearly all directions.
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Based on these results, the ejected winds are massive and carry far greater energy compared with the previously assumed smooth wind scenarios. Conventional theory suggested that all wind energy generated near black holes spreads throughout galaxies and controls galactic evolution. These new results overturn this understanding, indicating that wind energy barely spreads at all. Researchers are now compelled to reconsider the traditional theory of "coevolution," where galaxies and central massive black holes evolve together.
Lecturer Misaki Mizumoto from the Faculty of Education at the University of Teacher Education Fukuoka, a member of the research group, said: "Actually, before XRISM's launch, I predicted bullet-like winds and wrote a paper about it. However, I didn't expect such a pronounced phenomenon, and my first impression upon seeing the observation results was to wonder if there might be errors in data processing. But there were no mistakes, and I felt excitement as both 'as expected' and 'unexpected' feelings mixed together."
The research group is considering two possibilities: (1) bullet-like winds are only occasionally ejected, or (2) the winds pass through and escape via thin gas regions within galaxies.
Research Associate Kouichi Hagino from the Graduate School of Science at the University of Tokyo explained: "By investigating various black holes with XRISM, our understanding of how these winds affect coevolution will deepen."
The findings were published in the British scientific journal Nature on the 15th of May (Japan time), and the Japan Aerospace Exploration Agency (JAXA) announced them on the same day.
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Original article was provided by the Science Portal and has been translated by Science Japan.