Scientific Colloquium
June 3, 2011


"The Full Story on Eight Stellar-Mass Black Holes"

Starting in 1972 with Cygnus X-1, we now have mass estimates for a
good sample of 23 stellar-mass black holes, which are located in X-ray
binary systems.  During the past five years, we have measured the
spins of eight of these black holes.  The method we use is directly
analogous to the simple problem of determining the radius of a star of
known distance whose bolometric flux and temperature is known.  One
fits the thermal continuum X-ray spectrum of the black hole to the
relativistic thin-disk model of Novikov and Thorne, thereby
determining the radius of the inner edge of the disk.  We identify
this disk radius with the radius of the innermost stable circular
orbit (ISCO).  The ISCO radius scaled by the mass gives the spin
directly via an analytic formula.  By the No-Hair Theorem, our
measurements of spin and mass provide complete descriptions of these
eight black holes, while opening the door to experimentally testing
the Theorem.  I will discuss the implications of our spin data for
models of relativistic jets, gamma-ray bursts and black hole
formation.


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