(active Seyfert galaxy with well-studied SMBH)
IRAS 13224-3809 is a Seyfert galaxy on the order of a million
light-year distant. Its X-ray emission shows striking
variability and tts supermassive black hole has been studied with reverberation mapping,
yielding estimates of the SMBH size and mass.
One mass determination was 1.9×106 solar masses,
corresponding to a Schwarzschild radius of 8 solar radii,
which should be the same order-of-magnitude as the radius of its
event horizon, but somewhat different due to any rotation.
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