Michel Janssen (University of Minnesota) and Kiraniyot Gill (Harvard CFA)


Tuesday, April 23, 2019, 1:30pm to 2:30pm


BHI conference Room: 20 Garden Street, Cambridge (Lunch will be served at 1:00 pm)

Michel Janssen (University of Minnesota

Title:  Arch and scaffold: How Einstein found his field equations

Abstract: In his later years, Einstein often claimed that he had obtained the field equations of general relativity by choosing the mathematically most natural candidate. His writings during the period in which he developed general relativity tell a different story.

Based on an article co-authored with Jürgen Renn in Physics Today in November 2015 to mark the centenary of the first publication of the Einstein field equations.

Kiraniyot Gill (Harvard CFA)

Bayesian Reconstruction Perspectives of Gravitational Waves from Core-Collapse Supernovae in the Local Universe

After the measurement of gravitational waves from merging compact binary stars, the next grand challenge in gravitational-wave astronomy will be the detection of signals from the cosmic catastrophes that terminate the lives of massive stars. When the degenerate core of a star collapses to a neutron star or black hole, and the overlying shells are expelled in a supernova explosion, gravitational waves and neutrinos are the only means to directly probe such extreme processes. Due to the stochastic nature of the waveforms, detection from non-rotating progenitors covers events only within the neighboring five percent of our Milky Way Galaxy. Here we demonstrate the deterministic components in the signals can be identified in the data from current laser interferometers to distances of hundreds of kiloparsecs. This detection range exceeds previous estimates by two orders of magnitude and surpasses the range from a measured neutrino burst by a similar margin. The reconstruction techniques rely on Bayesian methods to discriminate the characteristic time-frequency tracks that are imprinted on the signals by quasi-periodic mass motions in the supernova core. Measuring these features will provide insights into explosion dynamics, the role of rotation in the star and its subsequent influence, and into the conditions in the near-surface layers of the new-born neutron star. This also introduces the possibility to trigger electromagnetic observations that can capture the shock breakout from the stellar surface to the rise of the early light curve. Thus astronomers will be enabled to study the structure near the surface of the star and in its immediate surroundings, which will unveil the mass loss of the progenitor prior to its collapse. Our work demonstrates the enormous potential of data analysis techniques for gravitational waves, which will offer unparalleled opportunities to probe the dynamics of the most energetic stellar phenomena in the Universe.