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1/2 An international research team, led by the University of Cambridge, has discovered a dormant overmassive black hole (BH) in the early Universe using JWST. The BH has a mass of 400 million times that of the Sun, but is accreting at a rate of only 0.02 times the (1) Eddington limit, so its discovery marks a turning point in our understanding of the formation and evolution of BHs. This BH, located in a galaxy existing only 800 Myr after the Big Bang, represents a significant challenge to current theoretical models. Its mass makes up about 40% of the total mass of its host galaxy, an extraordinarily high proportion compared to BHs in the local Universe, which typically make up only 0.1% of the mass of their galaxy. The BH, by accumulating matter at a very slow rate, is considered "dormant". Numerical simulations conducted by the research team suggest that long periods of inactivity are alternated with short phases of ultrafast growth. These models propose that BHs can exceed the Eddington limit for short periods, growing rapidly before entering long periods of dormancy. The discovery, published in "Nature" on 18 December 2024, challenges conventional theories on the formation of SMBHs, suggesting that they could be "born big" or go through cycles of hyperactivity and dormancy. The difficulty in detecting dormant BHs is due to their low luminosity, but the advanced instruments of the Webb telescope have allowed this object to be detected despite its inactivity. The detection of this dormant overmassive BH opens new perspectives for the study of accretion processes and galactic dynamics in the early universe, suggesting that there may be many other similar BHs yet to be discovered. Image: Artist’s impression of a black hole during one of its short periods of rapid growth Image Credit: Jiarong Gu --------------------------------------------- (1) The Eddington limit defines the maximum amount of matter that a black hole can accrete within a certain time frame, under conditions of equilibrium between the radiation pressure of the material around the black hole and its gravitational force. Both observations and theoretical models suggest that, under extreme conditions, this maximum threshold can be exceeded, at least for short periods.