M87* - the supermassive black hole in Messier 87

node · earth · Virgo Cluster, constellation Virgo as seen from Earth

The first black hole to be imaged, at the centre of the giant elliptical galaxy Messier 87 in the Virgo Cluster. The Event Horizon Telescope reported a mass of about six and a half billion solar masses and a distance of roughly 16.8 megaparsecs - some 55 million light-years - from an emission ring 42 microarcseconds across measured in April 2017 data. Two things make it the right first target despite its distance: its enormous mass gives it the largest angular shadow of any known black hole apart from Sagittarius A*, and its accretion flow changes on timescales of days rather than minutes, so a week of observation can be averaged into a single image without smearing. The measurement also settled a standing disagreement: stellar-dynamical modelling had given a mass near six and a half billion solar masses while gas-dynamical modelling had given roughly half that, and the shadow diameter agreed with the higher value. The ring is brighter on one side, which is read as relativistic beaming of material moving toward the observer. Not a place on Earth.