Stars and star clusters in the distant Universe seen through Einstein’s Lens

Abstract: Galaxy clusters are the most massive gravitational lenses Nature offers that really augment our observational capability to study celestial objects in the younger Universe using man-made telescopes. In recent years, a growing list of individual stars or clusters of stars that acquire large to extreme gravitational magnification factors have been uncovered with the Hubble Space Telescope and lately with James Webb. In this talk, I will explain how we understand the phenomenology of such extreme lensing phenomena, and what the potential use is for fundamental physics and astrophysics. I will first explain extremely magnified stars in the vicinity of lensing caustics, and discuss how they might be used to probe the theoretically predicted self-gravitating halos of Cold Dark Matter that are too small to host galaxies, as well as to probe minihalos possibly formed from QCD Axion Dark Matter that would be difficult to see otherwise. I will then talk about our recent study of newborn super star clusters in a magnified galaxy at Cosmic Noon, which represent one of the densest star-forming environments in the Universe. These systems are thought to be the progenitor of globular clusters but are no longer easily found in our cosmic backyard. Such studies can test the theory of how radiation, gas and gravity interact in the first ~ 10 million years of a crowded starburst when the most massive stars are still around.

Bio: Liang Dai received undergraduate physics education at Peking University in China. After that, he received his PhD at Johns Hopkins University in 2015 with thesis work on theoretical cosmology. He then worked from 2015—2020 at the Institute for Advanced Study in Princeton, and was a NASA Einstein Postdoc Fellow and then a John Bahcall Fellow. He joined the faculty of Berkeley’s physics department in 2020 and was awarded an Alfred P. Sloan research fellow in 2021.

Research Area: Astrophysics