The once-impossible black holes that could break thermodynamics — SkimNews
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A proof that extremal black holes form dynamically collapses the long-standing assumption that zero-temperature gravitational states are forbidden — meaning Hawking evaporation is not the inevitable fate of every black hole.
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- Christoph Kehle (MIT) and Ryan Unger (UC Berkeley) proved in 2024 that extremal black holes — long assumed to be an unattainable ideal — can actually form dynamically, with Kehle saying they "proved that wrong."
- The pair identified two viable formation mechanisms: gradually adding charged matter to a black hole, or firing a charged particle beam into empty space that collapses directly into an extremal black hole, and crucially neither path risks creating a naked singularity.
- Extremal black holes have zero temperature (no Hawking radiation) but retain entropy, making them unusually clean models for exploring black hole microstates — and linking idealized string theory calculations to objects that might genuinely arise in our universe.
- Chiara Toldo (Free University of Brussels) said the proof brings string theory's microstate-counting techniques "a step closer to the kinds of objects that might genuinely arise in our universe."
- Researchers showed last year that an extremal horizon's lack of damping would leave a distinctive fingerprint in the faint tail of radiation from infalling matter, though actual detection of an extremal black hole "remains a distant prospect."
- Kehle admitted the work made him realize "I understand black holes better than I understand classical thermodynamics," while Unger concluded: "We've disproved the third law as it was written, but we don't yet understand this problem in any sense."
Why it matters: The third law of black hole physics has been treated as a secure bridge between general relativity and thermodynamics since the 1970s; if that bridge has a hole, the entire analogy between black holes and thermodynamic systems may not be as exact as physicists believed. For string theorists, extremal black holes move from convenient fictions to potentially real objects, while Kehle's own concession hints at a deeper gap in how we define even ordinary thermodynamic processes.
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