Astronomers from Raman Research Institute (an autonomous institute of the Department of Science and Technology) and Arizona State University have discovered a mechanism by which supermassive black holes at galactic centers influence the circumgalactic medium (CGM), the diffuse gaseous reservoir extending 10–20 times beyond the galactic disk that provides fuel for star formation. The research, published in The Astrophysical Journal Letters (DOI 10.3847/2041-8213/ae9cbd), reveals that jets of hot plasma emitted by black holes interact with CGM gas, creating energetic jerks that ionize the gas and prevent it from cooling and collapsing into stars.
The team detected strong ionization signals specifically along the direction of the jets rather than uniformly around galaxies, indicating targeted energy deposition. The signal is strongest at two locations: where the jet first encounters the CGM at the edge of the stellar disk, and at the CGM's outer boundary where the slowed jet interacts with the gas. This energy deposition prevents gas clumping and star formation, effectively making galaxies "quiet and passive" despite the tiny relative size of black holes compared to their host galaxies.
Lead author Namrata Roy of RRI noted that the jet illuminates only the gas in its path rather than affecting gas equally in all directions. Co-author Sanchayeeta Borthakur of Arizona State University emphasized that black holes can shape galaxy evolution far beyond their immediate central regions. The research provides evidence for how energy from supermassive black holes regulates star formation on galactic scales, addressing a long-standing question in astrophysics about why extremely luminous galaxies with huge numbers of stars don't commonly exist.
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