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Astrophysical black holes (BHs) can be fully described by their mass andspin. However, producing rapidly spinning ones is extremely difficult as thestars that produce them lose most of their angular momentum before the BH isformed. Binaries where the progenitor is paired with a low-mass star in a tightorbit can produce rapidly spinning BHs (through tides), whereas those withmassive companions cannot (as they do not fit in such an orbit). A fewrapidly-spinning black holes (BHs) have been observed paired with very massivecompanion stars, defying stellar-formation paradigm. Models which reduce thestellar-core--envelope interaction (and winds) do not match observations northeory well; I show they also miss explaining the energetics. BH spins cannotbe produced during stellar collapse; using orbital spin throughexplosion-fallback material does not match the observations; spinning BHs upthrough accepted mass-transfer channels takes longer than their lifetimes, itis usually discarded. I show that fast mass-transfer mechanisms, predicted tomerge the BH and star, successfully spin the BHs up and show a mechanism toavoid said mergers and main dangers of the alternatives while naturallyexplaining the observations. The implications are potentially paradigm-shiftingand far-reaching in the high-energy, BH astrophysics context.

How To Spin Black Holes Up In High-Mass X-ray Binaries And Not Merge In The Attempt