BHI conference Room: 20 Garden Street, Cambridge (Lunch will be served at 1:00 pm)
Monica Pate, Harvard Physics
Title: "Gravitational Memory in Higher Dimensions"
Abstract: A precise equivalence among Weinberg's soft graviton theorem, supertranslation conservation laws and the gravitational memory effect was previously established in theories of asymptotically flat gravity in four dimensions. Moreover, this triangle of equivalence was proposed to be a universal feature of generic theories of gauge and gravity. In theories of gravity in even dimensions greater than four, we show...
Winning the Nobel Prize would cap most physicists’ careers. For 2017 winner Rainer Weiss, the prize might not even have been the biggest moment of his year.
The 85-year-old professor emeritus at MIT shared the Nobel Prize for Physics for conceiving and shepherding a set of observatories that allowed scientists to prove Einstein’s assertion about gravitational waves: accelerating objects send ripples cascading through the universe at light speed. The invisible waves are so faint that even the most powerful distort space-time by less than the width of a human...
This talk is devoted to Berryphases that appear in the context of asymptotic symmetries in general relativity. These phases arise when a coherent state is acted upon by symmetry transformations that trace a closed path in...
Andrea Puhm CNRS researcher, CPHT, Ecole Polytechnique, Black Hole Initiative Visiting Scholar
Title: On the distinguishability of black hole microstates
Abstract: A challenging question in the context of the information paradox is how to distinguish black hole microstates without having access to the entire spacetime. In the context of holography, one can ask how one can distinguish microstates of a black hole in anti-de Sitter space by measurements performed in the dual conformal field theory. I will discuss one...
Abstract: Over the last decade or so, dozens of x-ray or optical transient events have been detected towards the centers of (typically) low mass galaxies. They have been interpreted as the disruption of solar mass stars by the central supermassive black holes believed to lie in the centers of most galaxies. Such events were predicted in the 1970s. Early work indicated that the emission would be thermal, with temperatures of order 50 eV, arising from an accretion disk with an inner edge at or near the innermost stable circular orbit of the black hole, and would last a month or so. Loeb and Ulmer suggested that this disk radiation would be reprocessed into the near infrared, and that the event would last a decade or so. Early detections by ROSAT had spectral energy distributions (SEDs) dominated by soft x-rays. More recent events have been detected by optical transient surveys, and have SEDs dominated by UV emission. I will revisit the reprocessing arguments, and show that they actually predict that the emission should be in the UV rather than the near IR, and they further explain the observed constant effective temperature maintained while the luminosity first increases by a factor of ten, then decreases by a factor of 100.
Yichen Shi Black Hole Initiative
Abstract: We consider a rapidly spinning black hole surrounded by an equatorial, geometrically thin, slowly accreting disk that is stationary and axisymmetric. We analytically compute the broadening of electromagnetic line emissions from the innermost part of the disk, which resides in the near-horizon region. The result is independent of the details of the disk model and therefore universal. This is an example of critical behavior in astronomy that is potentially observable by current or future telescopes.
"Nonlinear Evolution of the AdS_4 Black Hole Bomb" Paul Chesler Black Hole Initiative
Abstract: Energy may be extracted from rotating black holes via scattering involving superradiant modes. It was suggested some time ago that if such modes could be confined using a mirror, then an amplification process can occur, converting a significant fraction of the black hole mass into radiation, leading to a so-called "black hole bomb." Anti-de Sitter spacetime contain a natural mirror - the timelike boundary of the geometry - and provides a tractable arena to study the nonlinear evolution of the black hole bomb. Via numerically solving the full 3+1 dimensional Einstein equations, I will present evidence that the AdS black hole bomb is a multistage process. Specifically, via superradiant gravitational modes, Kerr-AdS black holes transition to hairy black holes with a single Killing vector, which then experiences secondary weaker superradiant instabilities.
Peter Hintz University of California, Berkeley
Abstract: I will explain the point of view adopted in a number of recent works, joint with Andras Vasy, in which we prove the global non-linear stability of Minkowski space and of Kerr-(Newman-)de Sitter black holes. Instead of constructing and controlling the non-linear solution incrementally in time, we use a Newton-type iteration scheme: at each iteration step we solve a linearized equation globally. I will in particular address how this informs the choice of gauges, and highlight the crucial role played by constraint damping, first introduced as a tool in numerical relativity by Gundlach et al.