Scientists have introduced an updated approach to black hole thermodynamics that applies to objects that are growing, merging or evaporating. The work, led by researchers at Penn State, replaces the traditional event horizon with a dynamical horizon to overcome limitations in Stephen Hawking's original framework. It was published in Physical Review Letters.
Abhay Ashtekar, Atherton University Professor and Evan Pugh Professor of Physics Emeritus at Penn State, led the team. He noted that Hawking's laws were formulated only for black holes at equilibrium. "They were formulated for black holes at equilibrium, or unchanging over time, but black holes are constantly changing, they form, merge and eventually evaporate," Ashtekar said.
The new entropy measure connects more directly to a black hole's spin and energy. Co-author Daniel E. Paraizo explained that earlier models suggested infinite entropy and zero temperature, which conflicted with thermodynamics until Hawking incorporated quantum effects.
Co-author Jonathan Shu highlighted that event horizons rely on future events and fail for dynamic black holes. The dynamical horizon allows the first and second laws of thermodynamics to apply to nonequilibrium cases, supporting studies of mergers detected by LIGO-Virgo-KAGRA and evaporating black holes.
The research received support from the Penn State Atherton Professorship Program and the Eberly College of Science.