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The Dual Role of Black Holes in Galaxies

Supermassive black holes are common in large galaxies, such as our Milky Way, with some reaching staggering masses, even in the billions of times the mass of our sunsolar masses. Despite their considerable size, these black holes constitute a tiny fraction of their host galaxies' total mass, typically less than 1/1000.


However, far from being passive, these black holes exert an immense gravitational pull, drawing nearby matter toward them. As this matter spirals inward a massive black hole, it heats up due to friction, releasing significant energy that profoundly influences the evolution of the entire galaxyies.


This process is largely self-regulating, with the released energy having the potential to expel large amounts of gas entirely from the galaxies, effectively halting the formation of stars due to the reduced massstar formation. This demonstrates the profound impact supermassive black holes can have on their host galaxies, shaping their evolution significantly.


However, there's a twist. Under specific conditions, the energy liberated by accretion onto black holes can trigger vigorous star formation activity. In a recent paper published in The Astrophysical Journal Letters, Prof. Nusser and colleagues argue that these conditions are met in galaxies recently discovered by the James Webb Space Telescope (JWST). These galaxies appear to harbor an unusual high number of young stars and have formed large masses of stars within a few hundred million years thousand years of after the Big Bang, which raises questions about their formation and changes our understanding of early galaxy formation..


The answer may lie with black holes. JWST observations have revealed signatures of black holes in these early galaxies, suggesting that black hole activity may have played a role in triggering their rapid star formation. This discovery is remarkable and sheds light on the puzzle of large early galaxies: black hole activity serveds as a spark plug and triggeraccelerated for star formation.



Image credit: Illustration of the events described in the new paper Silk et al. 2024. The transition in star formation rates and black hole growth as redshift decreases from regimes where positive feedback dominates to a later epoch when feedback is largely negative.