BHI Colloquium


Tuesday, March 3, 2020, 1:30pm to 2:30pm


BHI Meeting Room

Mu-Tao Wang (Columbia University)

Title: On an invariant notion of angular momentum at null infinity

Abstract: We extend the earlier work of Chen-Wang-Yau and Keller-Wang-Yau to define total angular momentum of an asymptotically flat null hypersurface. This induces an angular momentum definition at any section of null infinity. We prove that this definition satisfies several invariant properties that include the BMS invariance.


Jose L. Gómez (Instituto Astronomico de Andalucía)

Title: The Sharpest View of Blazar Jets through Space and Millimeter VLBI Observations 

Abstract: Mass accretion onto the supermassive black holes that power AGN leads to the formation of highlycollimated relativistic jets that radiate across the entire electromagnetic spectrum, from radio to gamma-rays. Over the past decades, AGN jets have been repeatedly studied through centimeter VLBI observations, but the resolution provided is just a step behind the necessary to resolve the compact regions in the vicinity of the central black hole where jets are formed, collimated, and accelerated. This limitation has recently been overcome by two technological improvements. On one side, the space VLBI mission RadioAstron has allowed us to increase the virtual size of our VLBI telescopes to as large as the distance to the Moon, achieving angular resolutions as small as 20 microarcseconds. On the other side, the participation of ALMA in millimeter VLBI arrays, such as the EHT and GMVA, has not only allowed the EHT to capture the first image of a black hole, but also holds the potential to actually address for the first time the fundamental questions of how gravity works in the strong-field regime near the event horizon, how accretion leads to the formation of relativistic jets, and what are the sites and mechanisms for the production of high energy emission in blazars. In this talk we summarize the results from our RadioAstron Key Science Program, which in combination with quasi-simultaneous GMVA and EHT observations provide us the sharpest view of blazars jets to probe the magnetic field and innermost jet regions in a sample of the brightest blazars to test jet formation models.

See also: Astronomy, Math