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BLACK Report Summary

Project ID: 614199
Funded under: FP7-IDEAS-ERC
Country: France

Mid-Term Report Summary - BLACK (The formation and evolution of massive black holes)

Massive black holes, weighing millions of solar masses and above, inhabit the centers of today’s galaxies, including our own Milky Way. Massive black holes also power active galactic nuclei and quasars known to exist just a few hundred million years after the Big Bang. Black holes are expected to form in the first galaxies that form at early cosmic times. They then grow by accreting gas from their surroundings. When black holes are thus fed, they became powerful sources of both radiation and kinetic energy. A feeding/feedback cycle ensues: the black hole grows by accreting gas; the radiation and kinetic energy couple with the gas in the galaxy, modulating gas accretion onto the black hole, and star-formation in the galaxy. This feeding/feedback cycle, therefore, regulates both black-hole growth and galaxy growth.
In BLACK we separately tackle the three themes (formation, feeding and feedback) and then combine them in an organic way. In the first half of the project we have made significant progress on all the objectives regarding black hole formation, feeding and feedback.
Black hole formation: we have implemented black hole formation models in cosmological hydrodynamical simulations. We have supplemented these numerical experiments with analytical models that study regions that cannot be resolved in cosmological simulations. Our investigations showed that black hole formation is very sensitive to the environment and the detailed properties of the first galaxies.
Black hole feeding: we have studied, by means of analytical calculations and numerical simulations, the growth of black holes in galaxies. We have found that black hole growth in low-mass galaxies is suppressed, because supernova explosions blow away the gas from the central regions where black holes reside. Black hole growth is also suppressed in massive galaxies at late cosmic times, as these galaxies are progressively emptied of gas, which is turned into stars. We have throughout compared our theoretical investigations to observations, both of local galaxies and of distant ones.
Black hole feedback: we have used idealized galaxy simulations to study in great detail how feedback from the black hole heats and pushes away gas in its environment. We have coupled these idealized, but physically rich, simulations with cosmological simulations, more realistic in terms of environment, but lacking the high resolution that can be obtained in idealized cases. Bridging between different scales with different approaches allows us to connect these scales over an unprecedented dynamical range by using a combination of different techniques and codes, taking advantage of their different strengths.

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