Science › Black holes & quantum gravity
First pictures of a black hole (2019)
2019· Discovery / experiment
ProvenTested many times; part of working physics.
The Event Horizon Telescope's 2019 image of the black hole in galaxy M87, followed in 2022 by our own galaxy's.
See it on the Science map →How it works
No single telescope is sharp enough, so radio dishes across the planet observed at the same moment, with atomic clocks and hard drives, to act as one Earth-sized telescope. The data, taken in April 2017, showed a bright ring of hot gas around a dark shadow. M87's black hole weighs about 6.5 billion Suns, 55 million light-years away. The Milky Way's, Sagittarius A*, weighs about 4 million Suns.
Why it matters
It turned black holes from inference into something seen, and gave a new, direct test of general relativity in extreme gravity.
How we know
Released April 10, 2019 (M87*) and May 12, 2022 (Sagittarius A*). Several independent teams and imaging methods produced the same ring, and repeat observations in 2018 showed it again.
Still a mystery
Finer detail, such as the thin "photon ring" of light orbiting the hole, has not yet been resolved and may need telescopes in space.
Connections (2)
▸Black holes were photographed in First pictures of a black hole (2019)Proven
The relationship
A black hole itself emits no light, but gas swirling around it glows brightly. Gravity bends that light, forming a bright ring around a dark "shadow" about two and a half times wider than the horizon. A planet-sized network of radio telescopes, the Event Horizon Telescope, was sharp enough to resolve this ring for the giant black holes in M87 and the Milky Way.
How the link was found
The Event Horizon Telescope collaboration, more than 200 scientists, observed in April 2017 and released the M87* image on April 10, 2019; Sagittarius A* followed on May 12, 2022.
Why it's proven
Separate teams processing the data independently, with different methods, produced the same ring. Later observations in 2018 confirmed it persists, with the bright spot shifting as gas moves.
Open questions and mysteries
Finer structure, such as the thin "photon ring" of light orbiting near the hole, is not yet resolved.
▸First pictures of a black hole (2019) matched the shadow size predicted by General relativity: gravity is curved spacetimeProven
The relationship
General relativity predicts how strongly a black hole bends light, and so how large its dark shadow should appear for a given mass and distance. The Event Horizon Telescope measured M87*'s ring at about 42 microarcseconds across, roughly a donut on the Moon seen from Earth. That size matched relativity's prediction, using the mass measured from star motions.
How the link was found
The Event Horizon Telescope collaboration in 2019 for M87*, and in 2022 for Sagittarius A*, whose mass was known independently from decades of tracking nearby stars.
Why it's proven
Both shadows agreed with relativity to within about 10 percent, ruling out several alternative theories of gravity. Two very different black holes, 1,500 times apart in mass, fit the same prediction.
Open questions and mysteries
Sharper images could test relativity more precisely, including the predicted thin photon ring; current resolution cannot yet.