September 30th 2026, @IFT-UAM/CSIC

C/Nicolás Cabrera 13-15, Cantoblanco, Madrid.

Red Room

Zoom link:  tba

11:15h     Welcome coffee (ground floor cafeteria)

11:30h     First Talk

Speaker: Sameer Murthy (King's College, London, UK) 

Title: Near-extremal black holes in GR and in string theory

Abstract: What happens to the thermodynamics of a black hole at very low temperatures as it approaches extremality? This question had remained a puzzle for many decades. Recent progress shows that semi-classical physics in the near-extremal limit needs to be revisited due to the appearance of nearly gapless modes in the near-horizon of a near-extremal black hole. Upon approaching the extremal limit carefully, one finds that the quantum fluctuations of these gapless modes leads to unexpectedly large effects even for a very massive black holes with weakly-curved horizons. In the first part of this talk, I will explain this progress and discuss various applications.

In the second half of the talk, I will discuss progress regarding the calculation of entropy of supersymmetric black holes, which has been one of the big successes of string theory. I will discuss how the counting of entropy in string theory involves a subtlety regarding the supersymmetric index, and how its resolution also involves, once again, taking the extremal limit carefully. Finally, I will discuss how this procedure leads to a new class of supersymmetric solutions corresponding to black holes and black strings. 

15:00h     Second Talk

Speaker:  Luciano Rezzolla (Institute of Theoretical Physics, Goethe Univ., Frankfurt, Germany)

Title: Binary Neutron Stars: from macroscopic collisions to microphysics

Abstract: I will argue that if black holes represent one the most fascinating implications of Einstein's theory of gravity, neutron stars in binary system are its richest laboratory, where gravity blends with astrophysics and particle physics. I will discuss the rapid recent progress made in modelling these systems and show how the gravitational signal can provide tight constraints on the equation of state and sound speed for matter at nuclear densities, as well as on one of the most important consequences of general relativity for compact stars: the existence of a maximum mass. Finally, I will discuss how the merger may lead to a phase transition from hadronic to quark matter. Such a process would lead to a signature in the post-merger gravitational-wave signal and open an observational window on the production of quark matter in the present Universe.

16:00      Coffee (ground floor cafeteria)