Description:

The conditions near accreting compact objects are very extreme, creating environments which are difficult to replicate in laboratories on Earth. This includes objects such as neutron stars or stellar-mass black holes in binary systems, or supermassive black holes in the active centers of most galaxies, from which large quantities of high-energy radiation are produced. Most of this radiation can be observed in the X-ray band. By modeling the interaction of these X-rays with the gas near the black hole, and how this radiation will be affected after the interaction, it is possible to infer the key physical properties of both compact objects and the surrounding material. Specifically, combining the models with X-ray observations, we can obtain information about the black hole, for example whether it is spinning or not and how fast as well as information regarding the gas nearby, such as its composition, temperature, and dynamics. The accuracy of these models requires collection and curation of atomic parameters, numerical methods for radiative transfer, and detailed calculations of ionization and energy balance. The implementation of these models to interpret observational data requires specialized statistical techniques such as spectral fitting and Bayesian inference. We are actively working on developing and implementing all these tools in a variety of astrophysical problems, which include: measuring black hole spins using reflection spectroscopy; studies of disk-jet-corona connection in accreting sources using spectral-timing techniques (X-ray lags, power-spectra analysis, etc.); photoionization modeling of astrophysical plasmas at high-densities; development of advanced spectral-fitting techniques using machine-learning algorithms; to name a few. Importantly, high-resolution spectroscopy, timing analysis, and polarization modeling are currently the foremost aspects in modeling efforts for the next decade. 

Field of Science: Astrophysics
Advisors:

Javier Garcia Martinez
javier.a.garciamartinez@nasa.gov

Timothy Kallman
Timothy.R.Kallman@nasa.gov
(301) 286-3680