The Baryon Cycle in Massive Galaxies from the Bondi Sphere to the Halo

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Black holes are the most efficient power plants in the Universe. Fifty times more efficient than nuclear power, only one gram of matter falling toward a black hole every second could power the earth. Black holes are objects of infinite density surrounded by ghostly event horizons. An object wandering across the event horizon is swallowed and becomes lost to the universe forever. Not even light can escape. But how can power escape a black hole when nothing can escape it? ******Supermassive black holes weighing between one million and ten billion times the Sun lurk at the centres of all massive galaxies, including the Milky Way. Their enormous event horizons would enclose the entire solar system. As gas rushes toward a black hole it forms an accretion disk, much like water swirling down a drain. As the accretion disk spins around the event horizon, it becomes so hot that much of it is blown away as a wind of hot gas and radiation that permeates its entire host galaxy. Such an object, known as a quasar, is an early stage in the development of all massive galaxies. As nuclear black holes mature in size over billions of years of cosmic time, the energy of motion in an accretion disk is instead released in narrow, bipolar columns of particles, magnetic field, and radiation known as a radio jet. These jets and winds, travelling nearly at light speed, extend vast distances from the nucleus of the galaxy. The radio jets collide with the surrounding gas, preventing new stars from forming in the host galaxy. This mechanism, black hole feedback, is thought to govern the growth of galaxies.******Research led by my group over the past 15 years has shown how black hole feedback works at the centres of galaxy clusters. We discovered that radio jets inflate giant bubbles that rise like weather balloons through the tenuous atmospheres of galaxies and clusters. The bubbles heat the gas surrounding them on vast scales and apparently suppress the rate of star formation in their host galaxies. But how massive black holes are fueled is a mystery. Over the next five years my team will image cold molecular clouds that are likely fueling the jets and the stars forming around them. We will collect data from two of the most powerful telescopes in the world: the Atacama Large Millimeter Array (ALMA) and the earth-orbiting Chandra X-ray Observatory. We will use this data to study gas flows and winds in the gravitational grip of supermassive black holes. We will study the structure of the vast atmospheres surrounding galaxies where most of the energy released by black holes is captured and stored. Our ALMA Early Science program led to the discovery of massive, cold, molecular gas flows in galaxies that may have formed in the updrafts of giant X-ray bubbles. This program will reveal how molecular gas flows form and are powered, leading to a deeper understanding of their fundamental role in the formation and evolution of galaxies.