The case for hypercritical accretion in m33 x-7

Abstract

The spin parameter of the black hole in M33 X-7 has recently been measured to be a * p 0.77 ± 0.05. It has been proposed that the spin of the 15.65 M⊙ black hole is natal. We show that this is not a viable evolutionary path given the observed binary orbital period of 3.45 days since the explosion that would produce a black hole with the cited spin parameter and orbital period would disrupt the binary. Furthermore, we show that the system has to be evolved through the hypercritical mass transfer of-5 M⊙ from the secondary star to the black hole. © 2008. The American Astronomical Society. All rights reserved. Printed in U.S.A.