Statut  Confirmé 
Série  SEMGRECO 
Domaines  grqc 
Date  Lundi 2 Novembre 2020 
Heure  11:00 
Institut  IAP 
Salle  zoom details: contact pitrou@iap.fr 
Nom de l'orateur  Anson 
Prenom de l'orateur  Timothy 
Addresse email de l'orateur  timothy [dot] anson [at] th [dot] upsud [dot] fr 
Institution de l'orateur  LPT Orsay 
Titre  Disforming the Kerr metric 
Résumé  Starting from a recently constructed stealth Kerr solution of higher order scalar tensor theory involving scalar hair, we analytically construct disformal versions of the Kerr spacetime with a constant degree of disformality and a regular scalar field. While the disformed metric has only a ring singularity and asymptotically is quite similar to Kerr, it is found to be neither Ricci flat nor circular. Noncircularity has far reaching consequences on the structure of the solution. As we approach the rotating compact object from asymptotic infinity we find a static limit ergosurface similar to the Kerr spacetime with an enclosed ergoregion. However, the stationary limit of infalling observers is found to be a timelike hypersurface. A candidate event horizon is found in the interior of this stationary limit surface. It is a null hypersurface generated by a null congruence of light rays which are no longer Killing vectors. Under a mild regularity assumption, we find that the candidate surface is indeed an event horizon and the disformed Kerr metric is therefore a black hole quite distinct from the Kerr solution. 
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