Black Hole Imaging
Motivation and Context
Black holes, once considered a mathematical peculiarity of Einstein's General Relativity, are nowadays one of the most exciting research topics in Astronomy and Astrophysics. They induce an extreme gravitational environment making them a prime target for probing General Relativity and studying the conditions of the early universe. The Astro2020 decadal survey identified the effort to study black holes as a top priority for the coming decade. While black holes are not directly visible, the surrounding gas emits radiofrequency light which can be observed by radio telescopes. A black hole is predicted to leave a fingerprint in the form of a dark central shadow amid the surrounding bright gas.
Since 2020 I've been part of the Event Horizon Telescope (EHT) collaboration, working on imaging the black hole at the center of our galaxy: Sagittarius A* (Sgr A*, pronounced “sadge-ay-star”). Imaging Sgr A* is challenging due to its evolution, which is dynamic on the timescale of EHT acquisition. In May of 2022, we revealed the first images of Sgr A*. While these images certainly offer interesting insights, looking toward the future, I am developing new computational algorithms that aim to go beyond a 2D image. For example, could we use EHT observations to recover the dynamic evolution or even the 3D structure around a black hole? These novel computational challenges and algorithms are highlighted in SIAM News November 2022 Issue.
Using synchronized radio telescopes, the EHT is able to resolve structural features at the event horizon scale allowing it to image the invisible. Through a technique called Very Large Baseline Interferometry (VLBI), each telescope pair (or triplet) is sensitive to different spatial frequencies in the image. So, could more telescopes lead to exciting new scientific discoveries? Where should these telescopes be placed? What type of science could they extract? These are topics of great interest within the Next Generation EHT (ngEHT) group aiming to expand the current EHT network. Within the ngEHT, together with Paul Tiede and Daniel Palumbo, we are leading a working group focused on the science and technology of recovering 3D emissivity around a black hole (contact us if you are interested in contributing!).
Below are two short videos highlighting new computational algorithms for imaging the dynamic evolution and 3D structure around a black hole. For the papers, code, presentations and other materials see the project pages:
Short highlight clip from ICCV 2021
Short highlight clip from CVPR 2022
Aviad Levis*, Pratul Srinivasan*, Andrew Chael, Ren Ng, and Katherine Bouman, "Gravitationally Lensed Black Hole Emission Tomography", Proc. IEEE Conference on Computer Vision and Pattern Recognition, 2022.
Aviad Levis, Daeyoung Lee, Joel Tropp, Charles Gammie, and Katherine Bouman, "Inference of Black Hole Fluid-Dynamics from Sparse Interferometric Measurements", Proc. IEEE International Conference on Computer Vision, 2021.
Highlighted EHT Publications
Computational Imaging Sheds Light on the Black Hole in Our Galactic Center, SIAM News, November 2022.
Bringing a New Dimension into Black Hole Imaging, Caltech EAS Tech Brief, June 2022.
Caltech Researchers Help Generate First Image of Black Hole at the Center of Our Galaxy, Caltech Press Release, May 2022.