The Photon Ring in M87*

Kavli Affiliate: Lijing Shao

| First 5 Authors: Avery E. Broderick, Dominic W. Pesce, Paul Tiede, Hung-Yi Pu, Roman Gold

| Summary:

We report measurements of the gravitationally lensed secondary image — the
first in an infinite series of so-called "photon rings" — around the
supermassive black hole M87* via simultaneous modeling and imaging of the 2017
Event Horizon Telescope (EHT) observations. The inferred ring size remains
constant across the seven days of the 2017 EHT observing campaign and is
consistent with theoretical expectations, providing clear evidence that such
measurements probe spacetime and a striking confirmation of the models
underlying the first set of EHT results. The residual diffuse emission evolves
on timescales comparable to one week. We are able to detect with high
significance a southwestern extension consistent with that expected from the
base of a jet that is rapidly rotating in the clockwise direction. This result
adds further support to the identification of the jet in M87* with a black hole
spin-driven outflow, launched via the Blandford-Znajek process. We present
three revised estimates for the mass of M87* based on identifying the modeled
thin ring component with the bright ringlike features seen in simulated images,
one of which is only weakly sensitive to the astrophysics of the emission
region. All three estimates agree with each other and previously reported
values. Our strongest mass constraint combines information from both the ring
and the diffuse emission region, which together imply a mass-to-distance ratio
of $4.20^{+0.12}_{-0.06}~mu{rm as}$ and a corresponding black hole mass of
$(7.13pm0.39)times10^9M_odot$, where the error on the latter is now
dominated by the systematic uncertainty arising from the uncertain distance to
M87*.

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