This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A new study of nine nearby galaxies has shown that actively growing supermassive black holes may contribute to, rather than prevent, star formation in their host galaxies. The research, based on observations from the VLT/MUSE instrument, shows that active galactic nuclei (AGN), or bright regions powered by material falling into a supermassive black hole, are associated with star-forming rings or arcs, cone-shaped regions of energized gas, and fast "shocks," which occur when energy outflows interact with surrounding gas.
The findings, published today in The Astrophysical Journal, give a new perspective on how AGN feedback could influence the growth and evolution of galaxies. "Once we resolved them, we could see that they not only accrete things, but they also eject things," said Peixin Zhu, graduate student and astronomer at the Center for Astrophysics. "The injection and accretion are linked with each other." The study focused on galaxies whose central black holes are actively accreting, or pulling in, nearby material.
"We're seeing that black holes are not just consuming material at the centers of galaxies, but they're actively reshaping their surroundings," said Lisa Kewley, an astrophysicist at the Center for Astrophysics | Harvard & Smithsonian, director of the center and Zhu's adviser. "This work helps us understand a complex feedback cycle that plays an important role in galaxy evolution." The team used a new three-dimensional diagnostic technique to distinguish among three sources: star formation, radiation from the active black hole and excitation by shocks. Shock excitation occurs when high-speed outflows from the central black hole collide with the interstellar medium.
Across the sample, the researchers found that star-forming rings or arcs appeared at distances of about 0.8 to 6 kiloparsecs from the galactic center. Ionized cones of black-hole radiation extended outward from the galaxies' disks, while central regions dominated by fast shocks often extended perpendicular to those bicones. The researchers also found evidence for shocks in directions perpendicular to the AGN bicones.
Zhu notes that these shocks are broadly consistent with interactions between AGN jets and the interstellar medium, although winds from the active black hole may also contribute, particularly in galaxies with lower-power jets. "The most interesting phenomenon about shocks is that they always go perpendicular to where the black hole's injected outflows go," Zhu said. "It is very common, and we see it consistently appearing across all nine galaxies." The study's results combined high-resolution observations and detailed theoretical models.
The MUSE instrument provided spatially resolved optical data, while the state-of-the-art theoretical models built by Zhu and her colleagues, astrophysicists Kewley of the Center for Astrophysics and Ralph Sutherland of the Australian National University, allowed them to compare observations with predictions for black hole activity, star formation and shocks. Chandra X-ray observations also independently supported the researchers' interpretation. The results demonstrate that actively growing black holes have a complex cycle of accretion, outflow and interaction with their surrounding galaxies.
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