M87*

Key facts

Distance

≈ 55 million light-yearsAbout 16.8 megaparsecs

Mass

≈ 6.5 billion M☉

Event horizon diameter

≈ 38 billion kmNon-spinning estimate; about 250× the Earth–Sun distance

Ring size on the sky

≈ 42 microarcseconds

Host galaxy

Messier 87Giant elliptical in the Virgo Cluster

Constellation

Virgo

First image

10 April 2019From Event Horizon Telescope data taken in 2017

Jet length

≈ 5,000 light-yearsVisible optical jet

A true giant

M87* is about 1,500 times more massive than Sagittarius A*, the black hole at the centre of the Milky Way. If it does not spin, its event horizon is roughly 38 billion km across. Placed where the Sun is, it would swallow the orbits of all eight planets and Pluto many times over. Even light takes more than a day to travel across it.

Its host galaxy, Messier 87, is one of the largest galaxies in the nearby universe. It sits near the centre of the Virgo Cluster, a collection of more than a thousand galaxies, and it is surrounded by an unusually large swarm of globular clusters, numbering in the thousands. Such giant ellipticals often hold the biggest black holes, built up over billions of years of mergers and gas falling inwards.

The first image of a black hole

A black hole itself gives off no light, but the hot gas swirling just outside it does. Gravity bends that light around the black hole, producing a bright ring with a dark centre called the shadow. Seeing that ring for M87* required resolving a feature about 42 microarcseconds across, which is like reading a newspaper in New York from a café in Paris.

The Event Horizon Telescope achieved this by linking radio dishes from Hawaii to Spain and the South Pole, all observing at the same time and recording precise timestamps from atomic clocks. Combining the data turns the network into a virtual telescope as wide as Earth. Observations in April 2017 produced the image published in April 2019, after nearly two years of processing and careful checks.

The relativistic jet

In 1918 the American astronomer Heber Curtis noticed a 'curious straight ray' extending from the centre of M87. We now know it is a jet of electrons and other particles launched from close to the black hole and focused by twisted magnetic fields. It travels at very nearly the speed of light and glows across the spectrum, from radio waves to X-rays, as charged particles spiral in its magnetic fields.

Blobs within the jet sometimes appear to move faster than light. This is an illusion: when material moves almost straight towards us at close to light speed, the light it emits later has less distance to travel, which makes its motion across the sky look faster than it really is. Long-term radio monitoring has also found that the jet slowly wobbles with a period of about 11 years.

How M87* feeds

M87* is an active galactic nucleus, but by the standards of quasars it is a fairly gentle one. It swallows gas at a modest rate, a small fraction of a solar mass per year. Much of the energy released by that gas is carried away by the jet rather than radiated as light from a bright disc.

That jet has a large effect on its surroundings. Pumping energy into the hot gas that fills the Virgo Cluster, it heats the gas and stops it from cooling and forming new stars. In this way a single black hole, far smaller than its galaxy, helps regulate how the galaxy grows.

Surprising facts about M87*

• M87* weighs about 6.5 billion Suns, more than the combined mass of all the stars in some smaller galaxies.
• The light in the 2019 image left the black hole about 55 million years ago, not long after the dinosaurs died out.
• The Event Horizon Telescope's raw data were so large that hard drives had to be flown to processing centres instead of being sent over the internet.
• The jet was spotted in 1918, decades before anyone knew what powered it.
• Its event horizon is wide enough that light would need more than a day to cross it.

Frequently asked questions

What was the first black hole ever photographed?

M87*, the supermassive black hole in the galaxy Messier 87. The Event Horizon Telescope released its image on 10 April 2019, showing a bright ring of light around a dark shadow.

How big is M87*?

It has about 6.5 billion times the Sun's mass and an event horizon roughly 38 billion km across. That is larger than the orbits of all the planets in the Solar System.

How far away is M87*?

About 55 million light-years. Despite that distance, it appears roughly as large on the sky as Sagittarius A*, because it is so much bigger.

Is the black hole image a real photograph?

It is a reconstructed image built from radio observations by telescopes spread across Earth. Several independent teams and methods produced the same ring, which gives confidence that it is real rather than an artefact of the processing.

Why does M87* have a jet?

Gas spiralling into the black hole drags magnetic fields with it. The black hole's spin and those twisted fields are thought to launch and focus particles into two narrow beams moving at nearly the speed of light.

Keep exploring

• Sagittarius A*: supermassive black hole
• Gaia BH3: dormant stellar black hole
• Explore M87* in the interactive 3D Deep Space view
• Every Deep Space guide: black holes, stars, galaxies and the invisible universe

The 3D views in Ember’s Universe are scientific visualisations: physically based where possible, compressed or exaggerated where the real scales would hide everything.

Sources

• ESO — Astronomers capture first image of a black hole
• NASA — Messier 87
• NASA — Types of black holes