To capture the image, astronomers reached across intergalactic space to Messier 87, a giant galaxy in the constellation Virgo. There, a black hole several billion times more massive than the sun is unleashing a violent jet of energy some 5000 light years into space.

The image offered a final, ringing affirmation of an idea so disturbing that even Einstein, from whose equations black holes emerged, was loath to accept it. If too much matter is crammed into one place, the cumulative force of gravity becomes overwhelming, and the place becomes an eternal trap. Here, according to Einstein's theory, matter, space and time come to an end and vanish like a dream.

On Wednesday morning that dark vision became a visceral reality. As far as the Event Horizon team could ascertain, the shape of the shadow is circular, as Einstein's theory predicts.

The results were announced simultaneously at news conferences in Washington and five other places around the world, befitting an international collaboration involving 200 members, nine telescopes and six papers for The Astrophysical Journal Letters. When the image was put up on the screen in Washington, cheers and gasps, followed by applause, broke out in the room and throughout a universe of astrofans following the live-streamed event.

"Einstein must be totally chuffed," said Priyamvada Natarajan, an astrophysicist at Yale. "His theory has just been stress-tested under conditions of extreme gravity, and looks to have held up."

Kip Thorne, an astrophysicist at the California Institute of Technology who shared a Nobel Prize in 2017 for the discovery of gravitational waves from colliding black holes, wrote in an email: "It is wonderful to see the nearly circular shadow of the black hole. There can be no doubt this really is a black hole at the centre of M87, with no signs of deviations from general relativity."

Janna Levin, a cosmologist and professor at Barnard College in New York, said: "What a time to be alive."

A telescope the size of Earth

The image emerged from two years of computer analysis of observations from a network of radio antennas called the Event Horizon Telescope. In all, eight radio observatories on six mountains and four continents observed the galaxy in Virgo on and off for 10 days in April 2017.

The network is named after the edge of a black hole, the point of no return; beyond the event horizon, not even light can escape the black hole's gravitational pull.

The mystery of black holes has tantalised astronomers for more than half a century. In the 1950s, astronomers with radio telescopes discovered that pearly, seemingly peaceful galaxies were spewing radio energy from their cores - far more energy than would be produced by the ordinary thermonuclear engines that make stars shine.

Perhaps, astrophysicists thought, the energy was being liberated by matter falling onto supermassive, dense objects - later called black holes.

Since then, scientists have devised detailed models of how this would work. As hot, dense gas swirls around the black hole, like water headed down a drain, the intense pressures and magnetic fields cause energy to squirt from either side. As a paradoxical result, supermassive black holes can be the most luminous objects in the universe.

Einstein's least favourite idea

The unveiling took place almost exactly a century after images of stars askew in the heavens made Einstein famous and confirmed his theory of general relativity as the law of the cosmos. That theory ascribes gravity to the warping of space and time by matter and energy, much as a mattress sags under a sleeper.

To Einstein's surprise, the equations indicated that when too much matter or energy was concentrated in one place, space-time could collapse, trapping matter and light in perpetuity. He disliked that idea, but the consensus today is that the universe is speckled with black holes furiously consuming everything around them.

Many are the gravitational tombstones of stars that burned up their fuel and collapsed. But others, hidden in the centres of nearly every galaxy, are millions or billions of times more massive than our sun.

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Nobody knows how such behemoths of nothingness could have been assembled. Dense wrinkles in the primordial energies of the Big Bang? Monster runaway stars that collapsed and swallowed up their surroundings in the dawning years of the universe?

Nor do scientists know what ultimately happens to whatever falls into a black hole, nor what forces reign at the centre, where, theoretically, the density approaches infinity and smoke pours from nature's computer.

Zeroing in on cosmic monsters

Any lingering doubts about the reality of black holes dissolved three years ago when the Laser Interferometer Gravitational-Wave Observatory, or LIGO, detected the collision of a pair of distant black holes, which sent a shiver through the fabric of space-time.

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Still, questions about gravity and the universe abound. "We know there must be something more," Avery Broderick, a member of the Event Horizon team, told the audience in Washington. "Black holes are one of the places to look for answers."

Proving that the monsters in Virgo and the centre of the Milky Way were really black holes required measuring the sizes of their shadows. That was no easy job. Both are exceedingly small, at this distance, and resolving their tiny details would be a challenge for even the biggest individual telescope.

Moreover, the view is blurred by the charged particles such as electrons and protons that fill interstellar space. "It's like looking through frosted glass," said Doeleman.

To see into the shadows, astronomers needed to be able to tune their radio telescope to shorter wavelengths. And they needed a bigger telescope.

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Enter the Event Horizon Telescope, the dream-child of Doeleman. By combining data from radio telescopes as far apart as the South Pole, France, Chile and Hawaii, using a technique called Very Long Baseline Interferometry, Doeleman and his colleagues created a telescope as big as Earth itself, with the power to resolve details as small as an orange on the lunar surface.

In April 2017, the network of eight telescopes, including the South Pole Telescope, synchronised by atomic clocks, stared at the two targets off and on for 10 days.

For two years, the Event Horizon team reduced and collated the results. The data were too voluminous to transmit over the internet, so they were placed on hard disks and flown back to MIT's Haystack Observatory in Westford, Massachusetts, and the Max Planck Institute for Radio Astronomy in Bonn, Germany.

Last year the team divided into four groups to assemble images from the data dump. To stay objective and guard against bias, the teams had no contact with each other. They readied themselves for an inconclusive or ambiguous result - a blur, perhaps, that they couldn't quite read.

'It was a surprise how clear this image is'

Doeleman grew optimistic last year at a dinner attended by some of the younger members of the team, who showed him the first data for M87.

"There were clear signatures of a ringlike structure," he said. After dinner, he went to his office and made some crude calculations. "That was one of those great moments," he said. "It was a surprise how clear this image is."

The measurement also gave a firm estimate of the mass of the Virgo black hole: 6.5 billion solar masses. That is heavier than most previous determinations, and it suggests that the masses of other big black holes may need to be revised upward.

The telescope network continues to grow. In April 2018, a telescope in Greenland was added to the collaboration. Another observation run was made of the Milky Way and M87, and captured twice the amount of data gathered in 2017. That data was not part of the results released on Wednesday, but will be used to confirm them and monitor the behaviour of the black holes. Two more antennas are waiting to join the Event Horizon Telescope.

"The plan is to carry out these observations indefinitely and see how things change," said Doeleman, embarking on his new career as a tamer of extra-galactic beasts.

"It's astonishing to think humans can turn the Earth into a telescope and see a black hole," and still more amazing to do it with this team, he said. "That's the best."

The New York Times