Cold, clumpy accretion onto an active supermassive black hole

The so-called accretion flow that powers the growth of supermassive black holes in galaxy centres is assumed to be dominated by a smooth, steady flow of very hot plasma, but now observations instead reveal a clumpy accretion of very cold molecular clouds onto a supermassive black hole in the nucleus of a nearby giant elliptical galaxy. Cold gas accretion onto a supermassive black hole The so-called accretion flow that powers the growth of supermassive black holes in galaxy centres is often assumed to be dominated by a smooth, steady flow of very hot plasma, but there is little direct evidence to support this idea. New observations of the Abell 2597 galaxy cluster provide evidence for an alternative model, cold accretion onto black holes, recently predicted by simulations and theory, but not directly observed. The data reveal cold, clumpy molecular clouds falling towards an active supermassive black hole in the nucleus of a nearby giant elliptical galaxy. Supermassive black holes in galaxy centres can grow by the accretion of gas, liberating energy that might regulate star formation on galaxy-wide scales 1 , 2 , 3 . The nature of the gaseous fuel reservoirs that power black hole growth is nevertheless largely unconstrained by observations, and is instead routinely simplified as a smooth, spherical inflow of very hot gas 4 . Recent theory 5 , 6 , 7 and simulations 8 , 9 , 10 instead predict that accretion can be dominated by a stochastic, clumpy distribution of very cold molecular clouds—a departure from the ‘hot mode’ accretion model—although unambiguous observational support for this prediction remains elusive. Here we report observations that reveal a cold, clumpy accretion flow towards a supermassive black hole fuel reservoir in the nucleus of the Abell 2597 Brightest Cluster Galaxy (BCG), a nearby (redshift z = 0.0821) giant elliptical galaxy surrounded by a dense halo of hot plasma 11 , 12 , 13 . Under the right conditions, thermal instabilities produce a rain of cold clouds that fall towards the galaxy’s centre 14 , sustaining star formation amid a kiloparsec-scale molecular nebula that is found at its core 15 . The observations show that these cold clouds also fuel black hole accretion, revealing ‘shadows’ cast by the molecular clouds as they move inward at about 300 kilometres per second towards the active supermassive black hole, which serves as a bright backlight. Corroborating evidence from prior observations 16 of warmer atomic gas at extremely