= Thorne spin limit
{c}
{title2=$a_*\simeq0.998$}
The Thorne spin limit is the equilibrium spin produced by competition between coherent thin-disc matter accretion and capture of disc photons by a <Kerr black hole>. Preferential capture of counterrotating photon angular momentum prevents the standard radiatively efficient model from reaching $a_*=1$. The commonly quoted limit is approximately $0.998$, with some dependence on emission and accretion assumptions. https://articles.adsabs.harvard.edu/pdf/1974ApJ...191..507T[Thorne's original calculation] derives this result.
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