Coordinates near the horizon and null infinity in the Kerr spacetime

Alexander Grant (U Southampton)

Jan 12. 2026, 14:30 — 15:00

The usual Bondi-Sachs class of coordinate systems at null infinity, as well as the Gaussian null coordinate systems near an event horizon, are both examples of geodesic coordinates: the radial coordinate is a parameter along curves which are geodesic.  While the Eddington-Finkelstein coordinate systems in Schwarzschild are members of these classes (Bondi-Sachs for outgoing and Gaussian null for ingoing), the typically-used analogue in Kerr, Kerr-Newman coordinates, are not.  Over the past few decades, there have been many efforts to transform between Kerr-Newman coordinates and these coordinate systems, but each approach has at least one of the following issues: the transformation either 1) has been done necessarily perturbatively, 2) has not been based upon the null geodesics of Kerr, or 3) is very poorly behaved at the poles.  In this talk, I will discuss a new variation on an old approach which resolves all of these issues.

Further Information
Venue:
ESI Boltzmann Lecture Hall
Associated Event:
Hyperboloidal Foliations and their Application (Workshop)
Organizer(s):
Roland Donninger (U of Vienna)
David Hilditch (IST Lisboa)
Maciej Maliborski (TU Vienna)
Rodrigo Panosso Macedo (NBI, Copenhagen)
Alex Vañó Viñuales (U de Les Illes Balears)
Anil Colpan Zenginoglu (U of Maryland)