M87*

Messier 87 is a supergiant elliptical galaxy in the constellation Virgo, holding several trillion stars. Charles Messier catalogued it in 1781. In 1918 Heber Curtis noticed a “curious straight ray” coming out of its core. That ray is a jet of matter, at least 5 000 light-years long and moving at 80 to 85 percent of the speed of light, launched by the black hole at the galaxy’s centre: M87*.

The first picture of a black hole

In April 2017 the Event Horizon Telescope, a network of radio dishes spread across the planet that acts like one telescope the size of Earth, pointed at M87*. Turning the data into an image took two years. On 10 April 2019 the collaboration released the result, the first image ever made of a black hole: a dark shadow inside a lopsided ring of glowing gas.

The ring is about 690 AU across, more than ten times the width of Neptune’s orbit, yet from Earth it spans just 42 microarcseconds, a tiny fraction of the width of a human hair held at arm’s length. One side is brighter because the gas there is moving towards us at close to light speed, which boosts its light. From the size of the ring, the team measured the black hole’s mass at about 6.5 billion times the Sun’s.

Following up

In March 2021 the team released an image in polarised light, revealing how magnetic fields are arranged in the ring. In 2023 a re-analysis of the 2017 data produced a sharper version of the picture. The black hole has been given a Hawaiian name, Pōwehi, meaning “the adorned fathomless dark creation”, taken from the Kumulipo creation chant.

Its mass makes it about 1 500 times heavier than Sagittarius A*, the black hole at the centre of our own galaxy, which the same collaboration photographed in 2022.