The jets that shoot out of supermassive black holes do not stop at the edge of their galaxy. They heat gas 10 to 20 times farther out than the galaxy's visible stars reach, according to a study of hundreds of galaxies in The Astrophysical Journal Letters.
A black hole is tiny compared with the galaxy around it, yet astronomers have long suspected it can control whether the galaxy keeps making stars. New stars form from cool gas. Gas that is heated and charged cannot collapse into stars as easily.
"A black hole is incredibly small compared to a galaxy, but its impact can reach hundreds of thousands of light-years," says Namrata Roy of the Raman Research Institute, one of the authors.
Looking in the right direction
The team, led by Sanchayeeta Borthakur of Arizona State University, combined two large sky surveys. One, DESI, maps light from galaxies. The other, LOFAR, sees radio waves, which show where the jets point.
Around the galaxies, gas glowed in the light of charged hydrogen. The glow was much stronger along the direction of the jets than in other directions. That lines the heated gas up with the jets themselves.
What it may decide
Gas around a galaxy is its fuel for future stars. The authors say heating it could limit how many new stars the galaxy can form. Borthakur calls the result a solution to the long-standing question of how black holes shape their galaxies. Other astronomers have not yet tested it.
