Description:

Two 30 minute talks given by Nianyi Chen and Subo Dong.

Speaker: Nianyi Chen, Carnegie Mellon University

Title: Multi-messenger Signatures of Massive Black Hole Assembly Across Cosmic Time: Coupling Dynamics with Galaxy Formation Physics

Abstract: Massive black holes (MBHs) are among the most extreme astrophysical phenomena, and they play a ubiquitous role in shaping nearly all galactic ecosystems including our own Milky Way. Yet their birth place, birth time, and growth histories remain a mystery to us. In this talk, I will focus on the often neglected dynamical life of MBHs in cosmological galaxy formation simulations, which becomes crucial now given the recent observations of wandering BHs and future promises of probing MBH seeds through gravitational waves. I will show that with sub-grid dynamical friction (DF) treatments of gas and collisionless matter within large-volume cosmological hydrodynamical simulations, we can make a wide range of new theoretical predictions on the high-redshift MBH seed mergers, wandering MBHs in massive galaxies, and MBHs ejected from complex yet common multiple-galaxy interactions. I will then present a novel numerical framework to connect the statistical population of cosmological MBHs in galaxies, with high-resolution galaxy merger simulation with flexible star-formation and accretion models. This framework allows us to faithfully model MBH seed mergers and IMBH merger events within turbulent environments, which are currently challenging for cosmological volumes. The results will shed light on the early growth and assembly of MBHs through mergers, and the environments in which we expect to observe them.

Speaker: Subo Dong, Peking University

Title: Searching for “Lonely” Dark Objects with Microlensing

Abstract: Microlensing is the only known method to discover dark objects ranging from isolated stellar-mass black holes (BHs) down to Earth-mass free-floating planets (FFPs). The recent success of interferometric resolution of microlensed images with VLTI opens up a new venue for discovering isolated stellar remnants. I discuss how the VLTI-GRAVITY(+) instrument can significantly advance such discoveries, potentially leading to measuring the mass function of isolated stellar-mass BHs. Ground-based surveys have found more than a dozen ultra-short microlensing events, with the intriguing implication that FFPs are a few times more common than planets bound to stars. I will discuss the prospect of future space-based microlensing surveys to discover and characterize a large sample of low-mass FFPs.