Astronomers have found a directional signature of powerful black hole jets in gas far beyond the visible edges of galaxies. A study highlighted in a September 26 science report links the jets to hydrogen glowing in the vast reservoirs around galaxies, offering observational evidence of how activity at a galaxy’s center can affect its outer environment.
The team included Namrata Roy of India’s Raman Research Institute and Sanchayeeta Borthakur of Arizona State University. Their study appeared in The Astrophysical Journal Letters, while Arizona State University first announced the findings on September 24. The surrounding reservoir, called the circumgalactic medium, contains gas that can cool, move inward and provide material for new stars.
According to Arizona State University, the researchers combined optical observations from the Dark Energy Spectroscopic Instrument with radio measurements from the LOFAR Two-meter Sky Survey. They stacked faint signals from hundreds of galaxies with active jets and examined the H-alpha emission of ionized hydrogen along the jets’ directions.
The hydrogen signal was weak when measurements were averaged across all directions but became clear along the jet axes, the university said. It was especially bright near the visible galaxy and again toward the outer boundary of its gas reservoir. A separate check using magnesium absorption found cooler gas spread more evenly, without the same link to jet direction.
The pattern supports the idea that jets heat or disturb gas that might otherwise feed star formation, according to the researchers and India’s Department of Science and Technology. The observations identify where jets interact with gas; they do not directly measure how many stars failed to form as a result. That distinction matters when assessing how strongly black holes regulate galaxy growth.
Researchers say the directional method gives future optical and radio surveys a way to test the effect across other galaxies. Further observations and simulations can examine how much energy the jets deposit and whether the disturbed gas remains unable to cool over time.
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