New insights from JWST reveal how supermassive black holes and their galaxies formed together in the early Universe.
13.5 billions of years ago, black holes at the centers of tiny, dense early galaxies actually helped fuel new star formation. These galaxies were filled with dust and gas, ideal for early star formation. Therefore, the powerful energy outflows from the black holes compressed surrounding gas, sparking bursts of star formation. This process, known as positive feedback, continued for a while, until this trend started to shift.
Indeed, around 12.5 billion years ago (or at a redshift of about 5), the energy from black holes began to push gas out of the galaxies rather than compress it, leading to negative feedback where star formation slowed down.
One mistery, three possible solutions
This new picture, arising from a new research led by Joseph Silk (Sorbonne University, Paris) and collaborators, challenges the idea that galaxies were fully formed before they housed black holes. Overall, the findings suggest that these massive black holes might have been crucial players in shaping the first galaxies. But how could these ancient and massive black holes have formed in the first place? There are mainly three possibilities:
1) Black holes with relatively high initial masses could have formed from the collapse of supermassive Population III stars (the first generation of stars).
2) Another hypothesis is that a population of primordial black holes emerged during the earliest cosmic epochs. These black holes might represent a small fraction of dark matter (around 0.01%) and would have gained mass by accumulating gas, rapidly forming very massive black holes.
3) Finally, the third solution considers the formation of black holes through the direct collapse of enormous gas clouds in the primordial Universe. The mass of these clouds would collapse toward the center at a rate often too high to be counterbalanced by nuclear reactions, which, under more “normal” conditions, would end the collapse and give birth to new stars. When the central temperature reached 500 million degrees, the emission of neutrinos would further reduce the gas pressure opposing the further accumulation of mass, thus triggering the final collapse into a black hole.
References
Silk et al.; The Astrophysical Journal Letters, Volume 961, Issue 2, id.L39, 8 pp. (2024)
