Simulating Dense Gas in Active Galactic Nuclei, Tidal Disruption Events, and Supernovae

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Part 1Astronomy is an observational, not experimental, science. We cannot go to a star and directly measure its temperature, density, or how it makes energy. Rather, we discover these things by careful study of their light at different colors. Complex interactions between atoms and molecules produce light. The PIs are developing a large computer program, Cloudy, to predict this. Cloudy solves the complex equations of quantum mechanics and relativity. Astronomers use Cloudy to simulate what is happening in a distant star or galaxy and predict the emitted light. This is compared with what is seen through telescopes. This comparison makes it possible to understand what is happening. Cloudy is freely available and is among the more widely used codes in astronomy.The PIs will do two types of broader impact. They organize international workshops showing how to apply Cloudy to research projects. The Co-PI, a native of Spain, will visit local K-12 schools with large Hispanic populations. He does Spanish language talks and presentations. Hispanic students and their families visit the university for astronomy talks and viewing with the MacAdam Student Observatory.Part 2 Astronomy is an observational, not experimental, science. We cannot directly measure the temperature, density, or energy source for a star or galaxy. We discover these things by quantitative spectroscopy, the careful study of the observed spectrum. Astronomical sources are usually far from equilibrium. Their spectra depend on a number of thermal, plasma, chemical, and condensed matter processes. Analytical solutions are not possible. The code Cloudy solves all of this, numerically, to predict the spectrum. These predictions are compared that observations to infer properties of a star or galaxy. Cloudy is one of the more widely used theory codes in astrophysics with more than 300 papers citing its documentation per year.Cloudy has long solved these problems using available computers and atomic data. The simulations can be improved as computers become more powerful and the atomic data more accurate. We are developing techniques to improve modeling of the dense gas found near black holes or exploding stars. A full treatment of the "Rydberg levels," the highly excited orbits of electrons around ions, is the key improvement. This work will have an influence well beyond this project because of Cloudy's broad community use.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.