M87*

On 10 April 2019 the Event Horizon Telescope team showed the first image of a black hole, in the galaxy Messier 87. It is about 55 million light-years away and has a mass near 6.5 billion Suns.

The ring of light in the image is hot gas glowing as it falls toward the black hole.

Context

M87* sits at the centre of Messier 87, a giant elliptical galaxy in the Virgo cluster about 55 million light-years away. It was a natural first target for imaging because its black hole is enormous, so the shadow looks relatively large from Earth even at that distance.

The Event Horizon Telescope linked radio observatories on several continents, using a technique called very-long-baseline interferometry. The data were recorded in April 2017 on hard drives that had to be flown to central processing centres. It took about two years of calibration and analysis before the image was released on 10 April 2019.

The mass of about 6.5 billion Suns came from modelling the size of the ring. This agreed with the figure reached earlier from the motion of stars around the centre, although the two methods had earlier disagreed somewhat, so the exact number carries some uncertainty.

The image matched predictions from Einstein's general relativity for the shape of the shadow. Later work added polarised light measurements, which show how magnetic fields are arranged near the black hole and help explain how it powers a jet of material extending far into space.