Collaborative Research: Predicting the Observational Appearance of Accreting Black Holes

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Since black holes are by definition invisible, the only way that astronomers can detect them is by observing material accreting onto (or falling into) the black hole. Given the strong gravity, intense radiation and powerful magnetic fields near black holes, it is not surprising that such accretion is complex and can only be understood by running sophisticated numerical models on supercomputers. A research collaboration between the University of Illinois, Princeton University and the University of California-Berkeley will model the behavior of black-hole accretion in the realm intermediate between strong and weak accretion, when interesting effects such as jets of outflowing material and unusual oscillations in the accretion are known to take place. This work will help to unravel mysteries related to black holes, such as how the jets form and how the structure of the accretion flow changes over time. The team will communicate the excitement of black-hole astrophysics to the public through lectures and visualizations and to future generations of students through a black hole summer school.The theory of black-hole (BH) accretion and outflows is central to many areas of modern astrophysics and gravitational physics. The collaboration team has developed numerical techniques that permit nearly ab initio modeling of black-hole accretion in both the high- and low-accretion-rate limits. The team plans to develop new numerical techniques and codes suitable for studying the difficult intermediate-accretion-rate regime, which is associated with jets, quasi-periodic oscillations, and state transitions around stellar-mass black holes. Additions to the models include radiation forces, pair production and transport, nonthermal particle production and transport, and collisionless plasma effects, all of which are critical for making progress on long-standing problems in black-hole astrophysics, such as the structure and observational appearance (spectrum, time variability, polarization) of accretion at intermediate accretion rates, as well as questions about the origin and maintenance of large-scale magnetic fields believed to power relativistic jets from such systems. The group will make their new codes available for others to use through public releases.