Luca Comisso (Columbia University)
Passcode: 959078
Frankfurt am Main, Germany
Axial and polar ring down modes of a Schwarzschild black hole are calculated within General Relativity and a class of extensions. The modification considered includes a correction to the metric of leading order 1/r^4. This results in a mass-function depending on r. As a mass function, we use a particular one, which barely avoids the event horizon.
Zoom Meeting ID: 854 3210 3337
Passcode: 959078
A detection of non-Kerr features in astrophysical data concerning black holes would provide compelling evidence for the break-down of general relativity in the strong-field regime. While experiments have thus far validated the Kerr description, suppose we found that some object had a particular, non-Kerr structure; is there a clear way that this can be used to guide us towards the “true” theory of gravity? While a full answer to this problem is still far away, some recent progress has been made in that a recipe for constructing solutions to the inverse problem can be written down: given a metric (reconstructed from astrophysical data), it is shown how non-minimally coupled scalar-tensor and vector-tensor theories can be built around it. Some implications of this finding and other recent works are discussed.
Zoom Meeting ID: 854 3210 3337
Passcode: 959078
Astrophysical compact objects like neutron stars and accreting black holes are luminous sources of nonthermal radiation. Their activity demonstrates efficient dissipation of macroscopic energy stored in magnetic fields. A possible way for the dissipation can be a macroscopic MHD instability that excites turbulent motions in the tangled magnetic fields which, in turn, enables a transfer of energy to small scales where it can be dissipated. We performed 2D and 3D fully-kinetic radiative simulations of such reconnection-mediated turbulent flares in magnetized weakly-collisional pair plasmas. Turbulence is excited on a macroscopic scale and we observe that it develops by forming thin, dynamic current sheets on various scales. This gives rise to highly variable nonthermal flares whose characteristics we model in detail. Our fully-kinetic simulations can also be used to study the energy transfer mechanism of turbulent cascades themselves since they capture the dissipation processes from first principles.
Sergio Servidio (University of Calabria, Italy )