Physicists update Stephen Hawking’s black hole laws for dynamic events

Physicists are re-evaluating the fundamental laws governing black holes as new data and theoretical frameworks emerge. As of July 2026, researchers have highlighted two significant developments: the observational validation of Stephen Hawking’s area theorem using improved gravitational-wave detection and a proposed theoretical update to account for black holes that are not at equilibrium.

Observational confirmation of Hawking’s area theorem

On 14 January 2025, the LIGO-Virgo-KAGRA (LVK) collaboration detected a gravitational-wave signal, designated GW250114, which has provided the most precise evidence to date for a theorem first proposed by Stephen Hawking in 1971. Hawking’s area theorem posits that the total surface area of a black hole’s event horizon can never decrease over time.

The signal, observed by the Laser Interferometer Gravitational-Wave Observatory (LIGO) facilities in Washington and Louisiana, originated from two merging black holes. According to researchers, the combined surface area of the two objects before the merger was approximately 240,000 square kilometers. Following the merger, the resulting single black hole possessed a surface area of approximately 400,000 square kilometers. This growth confirms that the area of the event horizon increased, adhering to Hawking’s prediction.

Researchers achieved this level of precision by analyzing the "ringdown" — the final stage of the merger where the newly formed black hole vibrates like a struck bell. By measuring the pitch and duration of these gravitational waves, scientists were able to isolate distinct modes, allowing for an accurate calculation of the final black hole's mass and spin. This observational confirmation follows a tentative test performed in 2021, which relied on the signal from the first-ever detected black hole merger, GW150914. While the 2021 study had a confidence level of 95 percent, the new analysis of GW250114 reached 99.999 percent confidence.

The study also verified the Kerr metric, a 1963 mathematical solution by Roy Kerr that describes how rotating black holes behave. The consistency of the ringdown signal with mathematical models suggests that the resulting black hole is defined by its mass and spin.

Updating black hole thermodynamics for dynamic events

While the LVK collaboration focused on observational data, a separate team at Penn State has proposed a theoretical shift in how physicists handle black hole thermodynamics. Writing in Physical Review Letters, researchers led by Abhay Ashtekar, Atherton University Professor and Evan Pugh Professor of Physics Emeritus, argued that Hawking’s original laws of black hole mechanics carry a fundamental limitation because they were formulated for black holes at equilibrium — those that are unchanging over time.

"Hawking's laws of black hole mechanics provided a satisfying connecting between extreme and ordinary physics and have been the paradigm for 50 years, but they have a serious limitation. They were formulated for black holes at equilibrium, or unchanging over time, but black holes are constantly changing, they form, merge and eventually evaporate. We wanted to find a way to overcome this limitation and extend the laws to black holes that are out of equilibrium."

Abhay Ashtekar, Atherton University Professor and Evan Pugh Professor of Physics Emeritus at Penn State

The Penn State team contends that in dynamic, out-of-equilibrium situations, the event horizon is "teleological," meaning its properties depend on future events rather than local physics. Jonathan Shu, a graduate student in physics at Penn State and an author of the paper, noted, "These analogies only really work for a black hole that is at equilibrium. In dynamic situations, event horizons can form and grow in what we call flat regions of space-time, where nothing is happening. This makes them teleological -- their properties cannot be determined just by the local physics of the black hole but instead rely on prediction of events that may or may not happen in the future."

To address this, they have introduced the concept of a "dynamical horizon," which is defined by the black hole’s properties at a specific moment in time. This approach allows physicists to apply the laws of thermodynamics, specifically regarding entropy, to black holes that are actively growing, merging, or evaporating. The team suggests that this updated measure of entropy, which connects more closely to a black hole's spin and energy, could provide a more robust framework for interpreting future gravitational-wave detections.