New Estimates of the Spin and Accretion Rate of the Black Hole M87*

Abstract

In this Letter, we use the imaging results of M87* from the Event Horizon Telescope (EHT) to calculate the rotational velocity of the inner edge of the accretion disk and find a value of ∼0.14c. We then calculate the dimensionless spin parameter, a, of the black hole, obtaining a value of a ∼ 0.8. We deduce that this is probably a lower limit. We go on to use the results of the EHT polarization study of the magnetic field direction in the accretion disk of M87* as a proxy for the direction of motion of the spiralling accreting matter in this highly ionized disk. This direction is defined by the vector sum of the tangential rotation velocity and the inward radial accretion velocity. We thus calculate the accretion velocity to be ∼(7 ± 0.7) × 107 ms−1. We go on to estimate a range of values for the accretion rate from the inner disk to be ∼4 × 10−5 to ∼4 × 10−1 M⊙ yr−1, and a range of values for the accretion power to be ∼1034–1038 J s−1. This is the same range as the power of the jet, making it consistent with accretion-driven jet models.