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An illustration of a jet of energy cutting through the thick ring of dust around a supermassive black hole

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Supermassive black holes at the centres of large galaxies may clear the way for smaller satellite galaxies. Many large galaxies have satellite galaxies orbiting them, and the life cycles of these satellites are partially governed by the hosts’ supermassive black holes, in particular by the cosmic wind they spew out.

Ignacio Martín-Navarro at the Institute of Astrophysics of the Canary Islands in Spain and his colleagues examined 124,163 satellite galaxies using data from the Sloan Digital Sky Survey. They analysed which of these galaxies were “quenched” – meaning that they were no longer forming stars – and aimed to figure out how such galaxies were affected by the supermassive black holes at the centre of their hosts.

Some central black holes called active galactic nuclei (AGNs) have vast outflows of energy perpendicular to the plane of their galaxies, and these winds are powerful enough to affect the nearby satellite galaxies.

The team found that the satellites that orbited closer to the plane of their host galaxies were more likely to be quenched than those that orbited at an angle. “We actually were expecting for the satellites that were not in the host galaxy’s plane to be damaged by the AGNs,” says Martín-Navarro. “But we found the opposite effect.”

This may be because, rather than blasting the gas required for star formation out of the satellite galaxies, these energetic winds tend to create bubbles of space that are less dense than the surrounding areas. “It’s as if all this extra energy is sweeping out the particles that were there,” says Martín-Navarro.

The satellites that pass through these bubbles aren’t ramming through the dust and gas that normally fills the space around galaxies. Travelling through that material can strip away the gas needed for star formation, thereby quenching galaxies, but the areas cleared out by AGNs may be oases that allow the satellites to retain more material and continue cooking up stars.

Journal reference: Nature, DOI: 10.1038/s41586-021-03545-9

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