Yuan Li

TAC Postdoc Fellow
The Theoretical Astrophysics Center, Department of Astronomy
University of California, Berkeley

CV publications LinkedIn

About Me

I am a theoretical/computational astrophysicist, but occasionally work on observational data as well. My research interests include galaxies, galaxy clusters, black holes, AGN feedback, the interstellar medium, the intra-cluster medium and the circum-galactic medium.

I grew up in a small city of three million people in China, and obtained my PhD from Columbia University under the supervision of Prof. Greg Bryan. My thesis title is "AGN Feedback in Cool-Core Galaxy Clusters".

Please email me at yuan.astro *at* berkeley.edu if you would like to get in touch. You can also find me at Campbell Hall 459.

Supermassive Black Hole Feedback and Star Formation in Cooling Flow Galaxy Clusters

AGN jets trigger thermal instabilities in the intracluster medium by uplifting lower entropy gas to larger altitudes (link to paper). The figure on the left is a composite mock X-ray image of my simulated cluster. It shows both the ``positive'' and the ``negative'' sides of AGN feedback: the jets are triggering local thermal instabilities while driving volume-filling shock waves that heat up the whole central region of the cluster (link to paper). The interplay between cooling, AGN feedback and star formation causes clusters to go through billion-year-long cycles (link to paper).
Press release.Link to movies.A 3D visualization of the cold clumps.

Direct Detection of Black Hole-Driven Turbulence in the Centers of Galaxy Clusters

I use high-resolution ALMA and optical IFU data to study the kinematics of multi-phase gas in the centers of galaxy clusters. I measure the velocity structure function (VSF) of the filaments over a wide range of scales, and find that the motions of the filaments are turbulent. There is a clear correlation between features of the VSFs and the sizes of bubbles inflated by SMBHs, demonstrating that AGN feedback is the main driver of turbulence in cluster centers. The detection of turbulence near the mean free path suggests that isotropic viscosity is suppressed in the intracluster plasma. (link to paper).
Media coverage: ● Quanta Magazine.LiveScience.Space.com.

The Fate of AGB Winds in Massive Galaxies and Clusters

Asymptotic Giant Branch (AGB) winds from evolved stars produce dust grains. Due to the fast stellar velocity, the wind is thought to form a comet-like tail, similar to Mira in the Local Bubble. I have carried out both analytical and numerical studies of the interaction between an AGB wind and the surrounding hot gas, and find that the cooling time of the tail is inversely proportional to the ambient pressure. In high pressure environments, some of the gas in the mixing layer between the stellar wind and the surrounding hot gas can cool efficiently. I speculate that instead of thermal instability, the induced condensation at the mixing layer of AGB winds may be the origin of cold filaments in massive galaxies and galaxy clusters. This naturally explains the existence of dust and PAH in the filaments. (link to paper).

Correlations between Black Holes and Host Galaxies

I have studied black hole - host galaxy correlations in the Illustris and TNG100 simulations. Both simulations are able to produce black hole scaling relations in general agreement with observations at z = 0, but with noticeable discrepancies. In Illustris, the hosts of over-massive SMBHs have formed earlier and have lower present-day star formation rates, in qualitative agreement with the observations for massive galaxies. The findings show that simulated SMBH scaling relations and correlations are sensitive to features in the modeling of SMBHs (link to paper).

Outreach

Astronomy on Tap Ann Arbor
I founded AoT Ann Arbor along with grad students Aleksandra Kuznetsova and Erin May, and UM Astronomy faculty Keren Sharon. Check out the official website, facebook page, and the AoT paper.

Columbia Astronomy Outreach Program
I was an active member of the Columbia Astronomy Outreach Program while working on my PhD. My public lecture on black holes was featured in Columbia Spectator . I also participated in “Family Astro”, which included hands-on activities with children, and “Sidewalk Astronomy” where we carried 6" Dobsonians to the Adam Clayton Powell Plaza in Harlem and introduced astronomy to people on the street.

I was also a member of the Middle School Outreach Program organized by Prof. Mary Putman, which brought astronomy, in particular galaxies, into classrooms throughout New York City through in-class presentations. I also volunteered at various other one-time events including the Intrepid Sea, Air & Space Museum Space Shuttle Opening and the World Science Festival.