Events

Can Black Holes Evaporate Past Extremality?

Black holes with sufficiently large initial charge and mass will Hawking-evaporate towards the extremal limit. The emission slows as the temperature approaches zero, but still reaches the point where a single Hawking quantum would make the object superextremal, removing the horizon. We take this semiclassical prediction at face value and ask: When the emission occurs, what is revealed? Using a simple thin-shell model for the matter originally forming the black hole, we find that this matter *re-emerges* after the horizon is removed and subsequently expands back to large radius. This expanding remnant has been bathed in the ingoing Hawking quanta during evaporation and presumably carries correlations with the outgoing quanta, offering the attractive possibility of studying information paradox issues in a setup where spacetime curvatures are globally small, so that quantum gravity is not required. Even for ordinary black holes that evaporate down to the Planck size, we propose a radical new scenario for the interior: rather than forming a singularity, the collapsing matter settles onto an \textit{outgoing} null trajectory \textit{inside} the horizon for the entirety of evaporation.

Zoom

Monday, March 9, 2026 11:00 AM

Inperson
BHI Conference Room and Zoom

We present an overview of the thermal history of the Universe and the sequence of objects (e.g., protons, planets, and galaxies) that condensed out of the background as the Universe expanded and cooled. We plot (i) the density and temperature of the Universe as a function of time and (ii) the masses and sizes of all objects in the Universe. These comprehensive pedagogical plots draw attention to the triangular regions forbidden by general relativity and quantum uncertainty and help navigate the relationship between gravity and quantum mechanics. How can we interpret their intersection at the smallest possible objects: Planck-mass black holes (“instantons”)? Does their Planck density and Planck temperature make them good candidates for the initial conditions of the Universe? Our plot of all objects also seems to suggest that the Universe is a black hole. We explain how this depends on the unlikely assumption that our Universe is surrounded by zero density Minkowski space.

Zoom

Monday, March 9, 2026 9:30 AM

Inperson
BHI Conference Room and Zoom

Zoom

Monday, March 23, 2026 11:00 AM

Inperson
G10 and Zoom

Zoom

Monday, March 30, 2026 11:00 AM

Inperson
G10 and Zoom

Zoom

Monday, April 6, 2026 11:00 AM

Inperson
G10 and Zoom

Zoom

Monday, April 13, 2026 11:00 AM

Inperson
G10 and Zoom

Zoom

Monday, April 20, 2026 11:00 AM

Inperson
G10 and Zoom

Are We There Yet? First-principles Modeling of Multimessenger Signals in the Plasma Universe

Astrophysical black holes are surrounded by accretion disks, jets, magnetospheres, and coronae consisting of magnetized relativistic plasma. They produce observable multi wavelength and multi messenger signals from near the event horizon and it is currently unclear how this emission is exactly produced. The electromagnetic radiation typically has a non-thermal component, implying a power-law distribution of emitting relativistic electrons. Magnetic reconnection and plasma turbulence are viable mechanisms to tap the large reservoir of magnetic energy in these systems and accelerate electrons to extreme energies. The accelerated electrons can then emit high-energy photons that themselves may strongly interact with the plasma, rendering a highly nonlinear system. In some cases the electromagnetic emission is accompanied by a multi messenger signal in the form of neutrinos, cosmic rays, or gravitational waves. Modeling the emitting systems necessitates a combination of magnetohydrodynamic models to capture the global dynamics of the formation of dissipation regions, and a kinetic treatment of plasma processes that are responsible for particle acceleration, quantum electrodynamics effects like pair creation and annihilation, and radiation. I will present novel studies of accreting black holes and how they radiate in regions close to black hole event horizon, using both first-principles general relativistic kinetic particle-in-cell simulations and global large-scale three-dimensional magnetohydrodynamics models. With a combination of models, I determine where and how dissipation of magnetic energy occurs, what kind of emission signatures are typically produced, and what they can teach us about the nature of black holes.

Zoom

Monday, April 27, 2026 11:00 AM

Inperson
BHI Conference Room and Zoom