Black Holes Expand Through Gradual Processes Rather Than Galaxy Collisions

An analysis of over 2,400 galaxies with actively feeding black holes discovered that disk galaxies lacking central bulges grow black holes just as effectively as their bulged counterparts, suggesting galaxy mergers are not required for black hole growth. The findings align with theoretical simulations proposing that most cosmic black hole growth occurs through secular processes like gradual gas inflows along galactic structures rather than violent merger events. This challenges previous coevolution models and helps explain how James Webb observations have detected unexpectedly large black holes in high-redshift disk galaxies.

Researchers used spectroscopic data from the Dark Energy Spectroscopic Instrument to examine over 2,400 galaxies containing actively accreting black holes. Through sophisticated image analysis techniques, they identified 546 galaxies with minimal or absent central bulges—structures typically created by past merger events. These bulgeless systems demonstrated comparable black hole growth rates to their bulge-containing counterparts, suggesting that violent galactic collisions are unnecessary for supermassive black hole development.

The findings address a significant observational puzzle: early observations from the James Webb Space Telescope revealed unexpectedly massive black holes in distant disk galaxies, which contradicted established relationships between black hole and galaxy properties. Additionally, astronomers discovered more disk galaxies in the ancient universe than predicted, raising questions about how such delicate structures could survive and how their black holes could develop without merger-driven growth mechanisms.