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Magnetic Brakes for Cosmic Spinning Tops ✛

Original: "Spinning into the Gap: Direct-Horizon Collapse as the Origin of GW231123 from End-to-End GRMHD Simulations"
· Ore Gottlieb, Brian D. Metzger, Danat Issa, Sean E. Li, Mathieu Renzo, Maximiliano Isi
arXiv:2508.15887 · 2025-08-21 · CC BY 4.0 · 1 min
High Energy
How magnetic fields, like brakes, control the mass and spin of black holes, explaining the strange findings of gravitational wave detectors.

When the core of a dying star collapses, a black hole is born — a cosmic spinning top. The stronger the collapse, the faster the spin. But this top has a magnetic brake: a strong field flings some matter away, slowing the hole, while a weak field lets matter fall in and spin it up to nearly the speed of light.

This is exactly what explained the mysterious hole pairs spotted by gravitational wave detectors — instruments built by Rainer Weiss and his colleagues. Event GW231123 revealed holes with masses thought impossible: stars with such cores were expected to explode as supernovae leaving nothing behind. But simulations confirmed: with rapid rotation and a moderate magnetic field, the star collapses into a heavyweight hole.

The same magnetic fields that brake the hole can also create jets — streams of matter that outshine galaxies and are visible across the universe. The fruit of nearly a century of effort: Schwarzschild described the stationary hole, Thorne the spinning one, and new calculations have merged their ideas.

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It was once thought that the core of a star with 250 solar masses would explode without a trace. It turns out it can produce a black hole.

Such a rapidly spinning hole is almost like Gargantua from Interstellar: extreme rotation and monstrous gravity.

\ell(r,\theta) = \begin{cases} 0.55 r^2 \sin^2\theta \, \text{s}^{-1} & r < r_c \\ 0.55 r_c^2 \sin^2\theta \, \text{s}^{-1} & r_c < r < R_{\text{He}} \end{cases}
Rotation profile: the inner part rotates rigidly, the outer part maintains constant angular momentum.
a = \frac{c}{G M_{\text{BH}}^2} \int_0^{M_{\text{BH}}} \ell(m) \, dm
Spin is computed as an integral of specific angular momentum over the mass accreted by the black hole.
Scientists
John Archibald WheelerJacob BekensteinFritz ZwickyKarl SchwarzschildStephen HawkingSubrahmanyan Chandrasekhar
Concepts
direct collapse black holes binary black hole hills mechanism gw190814 gamma ray burst merger helium burning neutron star binary merger ringdown collapse bubble collision mass inflation nuclear reaction mass gap inspiral helium star effective spin tidal disruption event gravitational instability inner horizon galactic bulge m87