Delivered by a Binary: Hills-Capture Budgets for the Origin of the S-Stars

The S-stars pose a delivery problem: massive young stars should not form where they are found, in the tidal field of the black hole, yet there they orbit. The leading delivery mechanism tears a binary apart at the hole, capturing one star and ejecting the other at extreme speed. This paper computes the budgets of that mechanism. A binary of two solar-mass stars with a separation of 0.1 AU, disrupted at its tidal radius of 12.9 AU, leaves its captured member on an orbit of semi-major axis 1665 AU and period 32.8 years, squarely in the S-star range, while the ejected member leaves at 1513 kilometres per second, well above the Galaxy's escape speed of about 550 kilometres per second, joining the hypervelocity population actually observed in the halo. The catch is in the shape: the captured orbit's eccentricity is 0.992, higher than most observed S-star eccentricities, the well-known tension that subsequent dynamical evolution must relieve. Wider binaries capture onto wider orbits and eject more gently, as the tabulated grid shows. Computed from the standard capture scalings and published stellar parameters.