It looked like a flaming orange, yellow and black ring.

"We have seen what we thought was unseeable. We have seen and taken a picture of a black hole. Here it is," said Sheperd Doeleman of Harvard.

Jessica Dempsey, a co-discoverer and deputy director of the East Asian Observatory in Hawaii, said it reminded her of the powerful flaming Eye of Sauron from the Lord of the Rings trilogy.

The data was gathered by eight radio telescopes around the world, in a milestone in astrophysics.

The research was conducted by the Event Horizon Telescope project, an international collaboration begun in 2012 to try to directly observe the immediate environment of a black hole.

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

Taken over four days when astronomers had "to have the perfect weather all across the world and literally all the stars had to align", the image helps confirm Albert Einstein's general relativity theory, Dempsey said. Einstein a century ago even predicted the symmetrical shape that scientists just found, she said.

"It's circular, but on one side the light is brighter," Dempsey said. That's because that light is approaching earth.

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.

Black holes, phenomenally dense celestial entities, are extraordinarily difficult to observe despite their great mass. A black hole's event horizon is the point of no return beyond which anything - stars, planets, gas, dust and all forms of electromagnetic radiation - gets swallowed into oblivion.

"This is a huge day in astrophysics," said US National Science Foundation director France Cordova. "We're seeing the unseeable."

The fact that black holes 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.

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 telescope data was gathered by the Event Horizon Telescope two years ago, but it took so long to complete the image because it was a massive undertaking, involving about 200 scientists, supercomputers and hundreds of terabytes of data delivered worldwide by plane.

The team looked at two supermassive black holes, the M87 and the one at the center of our own Milky Way galaxy. The one in our galaxy is closer but much smaller, so they both look the same size in the sky. But the more distant one was easier to take pictures of because it rotates more slowly.

Australian Associated Press