The image reveals the black hole at the centre of Messier 87, a massive galaxy in the nearby Virgo galaxy cluster. This black hole resides about 54 million light-years from Earth.

The image shows the boundary between light and dark around a black hole, called the event horizon - the point of no return, where the gravity of the black hole becomes so extreme that nothing that enters can ever escape. Whatever gets sucked in - stars, planets, gas, dust and all forms of electromagnetic radiation - are swallowed into oblivion.

At the centre of the black hole, time and space become so curved upon themselves that the laws of physics break down completely.

Black holes, phenomenally dense celestial entities, are extraordinarily difficult to observe despite their great mass. The fact that they do not allow light to escape makes viewing them difficult. The scientists look for a ring of light - disrupted matter and radiation circling at tremendous speed at the edge of the event horizon - around a region of darkness representing the actual black hole. This is known as the black hole's shadow or silhouette.

Scientists say they observed the source for four days.

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The announcement was made in simultaneous news conferences in Washington, Brussels, Santiago, Shanghai, Taipei and Tokyo.

The project's researchers obtained the first data in April 2017 using telescopes in the US states of Arizona and Hawaii as well as in Mexico, Chile, Spain and Antarctica.

Since then, telescopes in France and Greenland have been added to the global network. The global network of telescopes has essentially created a planet-sized observational dish.

The existence of black holes, one of the more mysterious objects in the cosmos, has been universally accepted even though little is known about them. Black holes form from remnants of a large star that dies in a supernova explosion. Scientists estimate there could be as many as a billion black holes in the Milky Way, according to NASA.

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The EHT's work focuses on two super-massive black holes - the first, dubbed Sagittarius A* - sits at the centre of the Milky Way with a mass of about 4.3 million times that of the sun and located 25,000 light years from Earth.

The second lies at the core of the M87 elliptical galaxy, about 50 million light years from Earth, and is 1500 times more massive than the Sagittarius A-star.

"The gates of hell"

Heino Falcke, Professor of Astroparticle Physics and Radio Astronomy at the Radboud University Nijmegen and chairman of the EHT Science Council, said: "In the picture we are looking at a region we cannot imagine, the gates of hell, the point of no return. To me, it's awe-inspiring, but it's also important for physics.

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"If immersed in a bright region, like a disc of glowing gas, we expect a black hole to create a dark region similar to a shadow - something predicted by Einstein's general relativity that we've never seen before," Falcke said.

"This shadow, caused by the gravitational bending and capture of light by the event horizon, reveals a lot about the nature of these fascinating objects and allowed us to measure the enormous mass of M87's black hole."

US National Science Foundation Director France Córdova said: "This is a huge day in astrophysics. We're seeing the unseeable."

Feryal Ozel, an astrophysicist at the University of Arizona and member of the science council for the EHT, called the result the highlight of her career.

"We are able to image one more object in the universe that ... at one point people thought could not be possible," she said. "It hits that human explorer spirit. We got another look into the unknown."

Astrophysicist Monika Moscibrodzka from Radboud University Nijmegen said, "The size is always the same, it doesn't change and we measured the contrast between the ring itself and the central darkness.

"This kind of structure can only be formed if something is rotating - could be matter around it or black hole itself. Images give sense of direction of rotation, which is clockwise. We are looking at the shadow of the black hole."

Astrophysicist Dimitrios Psaltis of the University of Arizona, the EHT project scientist, said, "The size and shape of the shadow matches the precise predictions of Einstein’s general theory of relativity, increasing our confidence in this century-old theory."

"Imaging a black hole is just the beginning of our effort to develop new tools that will enable us to interpret the massively complex data that nature gives us," Psaltis added.

The images represent a major scientific accomplishment and "an opportunity to rethink the cosmos and our place in it", Priyamvada Natarajan, a professor of astronomy and physics at Yale University, wrote in an opinion article for The New York Times.

Reuters, Bloomberg, The Washington Post