A Black Hole’s Jets May Feed an Entire Galaxy
Rendering of Black Hole with Jets
Galaxies are enormous and hold hundreds of billions of stars. These stars form from cold, dense gas. Every large galaxy, including the Milky Way, is wrapped in a huge envelope of gas called the circumgalactic medium, or CGM. This reservoir of raw material stretches 10–20 times the size of the visible portion of the galaxy.
Astronomers have found a faint glow along black hole jets hundreds of thousands of light-years from their source. It offers a clue to how galaxies can run short of fuel for new stars.
A galaxy does not end where its visible stars end. Beyond them lies an enormous, faint envelope of gas called the circumgalactic medium. Some of that gas can cool, move inward and supply the raw material for new stars. A new study suggests that jets launched near a galaxy’s central black hole can alter that reservoir far beyond the galaxy’s visible edge. ASU News
The evidence is a glow from hydrogen gas. Researchers combined observations of hundreds of galaxies with active radio jets, using optical data from the Dark Energy Spectroscopic Instrument and radio measurements from the LOFAR Two-meter Sky Survey. The hydrogen signal was too faint to stand out around an individual galaxy. But when the team combined the observations and looked along the jets’ paths, it became clear. Averaged across all directions, it was weak. ASU News
That difference matters. The gas was not glowing evenly around the galaxies; its brightest signal followed the direction of the jets. The researchers also found brighter regions close to the galaxies and farther out near the edge of the surrounding gas. A separate measure of cooler gas, traced through magnesium absorption, did not show the same alignment. Together, those results point to the jets leaving a directional imprint on the gas they encounter. ASU News
Why would a black hole affect a galaxy on such a vast scale? As material falls toward an active supermassive black hole, the region around it can launch fast streams of plasma. Those jets carry energy outward into the galaxy’s gas supply. If they heat or disturb enough of that gas, less may cool and flow inward to form stars. The new observations show where that interaction may be happening; they do not directly measure how much future star formation each jet prevents. ASU News
The finding also helps explain why the signal was difficult to detect before. Looking at a galaxy’s surroundings as though they were the same in every direction washes out an effect concentrated along two narrow paths. By matching the faint hydrogen measurements to the radio jets’ orientation, the team brought that pattern into view. ASU News
The picture emerging is of a black hole influencing more than its immediate neighborhood. Its jets can reach into the distant gas reservoir on which a galaxy depends. Whether that ultimately slows star formation in a particular galaxy remains a question for further study, but astronomers now have a clearer place to look for the answer. ASU News
Source: Arizona State University. (2026, September 24). Black hole jets may shape the fate of entire galaxies. https://news.asu.edu/b/20260924-black-hole-jets-may-shape-fate-entire-galaxies
Study: Borthakur, S., Roy, N., et al. (2026). The Astrophysical Journal Letters. https://doi.org/10.3847/2041-8213/ae9cbd
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