BHI Colloquium


Tuesday, November 12, 2019, 1:30pm to 2:30pm


BHI Meeting Room

Pengyu Le (U. of Michigan)

Title: On the Penrose inequality
Abstract: The Penrose inequality is a far reaching inequality in GR proposed by Penrose in 1973. It conjectures a simple relation between the total mass of the spacetime and the mass of any black hole inside it. The original reasoning supporting this inequality by Penrose relates it to some of the most important and difficult problems in GR, i.e. the final state of evolution of black holes and naked singularity (the weak cosmic censorship conjecture). A major breakthrough was achieved independently by Huisken, Ilmanen and by Bray. They proved a very general case of the inequality, i.e. the Riemannian Penrose inequality. The Riemannian Penrose inequality is of course not the end of the story. There are versions of the inequality on general initial data sets and on null hypersurfaces, and also stronger versions involving electric charge and angular momentum, which are still widely open. The speaker will present his recent work confirming the Penrose inequality on null hypersurfaces in a perturbed Schwarzschild spacetime.

Jim Braatz (NRAO)

Title: Measuring Black Hole Masses and the Hubble Constant with H2O Megamasers

Abstract: Water vapor maser emission is detected in the circumnuclear, edge-on accretion
disks of about 30 nearby active galaxies.  These masers orbit within a parsec of the central supermassive black hole and reveal Keplerian rotation profiles. 
They provide the only means of directly mapping the sub-parsec accretion disks in AGNs, and give gold-standard masses for the supermassive black holes.  In a few cases, they can be used to determine angular size distances to the host galaxies, allowing a geometric measurement of the Hubble Constant.  In this talk, I will describe progress in discovering and mapping these maser systems, highlight the significance of determining the Hubble constant using a geometric, one-step measurement, and discuss prospects for using ALMA and the ngVLA to expand on studies of megamasers.

Alfredo Guevara (Perimeter Institute)

Title: Classical Spinning Black Holes and Quantum Field Theory Amplitudes

Abstract: Following the advent of LIGO measurements, it has been observed that Quantum Field Theory amplitudes can be used to derive physical observables appearing in a classical scattering of two black holes, or even more general compact objects. Such observables can be computed to high orders in perturbation theory and can be nicely mapped to the Post-Newtonian or Post-Minkowskian treatment of the binary inspiral problem. In this talk we will outline recent progress in this direction focusing on the case of two spinning black holes. For this we first show how amplitudes unveil new structures inside the Kerr solution, which simplify aspects such as the multipole expansion or gravitational radiation.