Using a global network of telescopes to see the “invisible”, an international scientific team announced on Wednesday an important step in astrophysics – the very first picture of a black hole – in a realization that validated a pillar of science advanced by Albert Einstein over a century ago.
Black holes are monstrous celestial entities with gravitational fields so vicious that any matter or light can escape. The photo of the black hole in the centre of Messier 87, or M87, a massive galaxy in the relatively nearby Virgo galaxy cluster, shows a bright red, yellow and white ring surrounding a dark centre.
The research was conducted as part of the Event Horizon Telescope (EHT) project, an international collaboration that began in 2012 to attempt to directly observe the immediate environment of a black hole using a global network of terrestrial telescopes. The announcement was made at simultaneous press conferences in Washington, Brussels, Santiago, Shanghai, Taipei and Tokyo.
The team’s observations strongly validated the general relativity theory proposed in 1915 by Einstein, the famous theoretical physicist, to explain the laws of gravity and their relationship to other natural forces.
“We accomplished something that was thought impossible just a generation ago,” said astrophysicist Shepherd Doeleman, director of the Event Horizon Telescope at the Center for Astrophysics, Harvard & Smithsonian.
Doeleman said the research “verifies Einstein’s theory of gravity in this most extreme laboratory.”
Black holes, celestial entities of phenomenal density, are extraordinarily difficult to observe by their very nature despite their large mass. The event horizon of a black hole is the point of no return beyond which everything – stars, planets, gas, dust and all forms of electromagnetic radiation – is swallowed up in oblivion.
The fact that black holes do not allow light to escape makes it difficult to observe them. Scientists are looking for a ring of light – hot disturbed matter and radiation that rotates at a dazzling speed on the edge of the event’s horizon – around a region of darkness representing the real black hole. This is called the shadow or silhouette of the black hole.
Scientists have said that Einstein’s theory predicted that the shape of the shadow would almost be a perfect circle – as it turned out to be.
Astrophysicist Dimitrios Psaltis of the University of Arizona, the EHT project scientist, said: “The size and shape of the shadow correspond to the precise predictions of Einstein’s general theory of relativity, increasing our confidence in this century old theory.
“Imaging a black hole is only the beginning of our efforts to develop new tools that will allow us to interpret the extremely complex data that nature provides us,” added Psaltis.
“Science fiction has become a fact of science,” said Daniel Marrone, professor of astronomy at the University of Arizona.
The project researchers obtained the first data in April 2017 using radio telescopes in the American 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 has essentially created an observation antenna the size of a planet.
The project also targeted another black hole – Sagittarius A* is located in the centre of our own Milky Way galaxy – but did not announce any photos of it, although scientists expressed optimism that such an image would be obtained. Sagittarius A* has 4 million times the mass of our sun and is 26,000 light years from Earth.
Types of Black Hole:
According to theory, there could be three types of black holes: stellar, supermassive and miniature black holes – depending on their mass. These black holes would have formed in different ways.
Star black holes form when a massive star collapses. Supermassive black holes, which can have a mass equivalent to billions of suns, probably exist in the centres of most galaxies, including our own Milky Way galaxy. We do not know exactly how supermassive black holes are formed, but they are likely to be a by-product of galaxy formation. Due to their location in the centre of galaxies, close to many tight stars and gas clouds, supermassive black holes continue to grow due to a regular diet of the material.
No one has ever discovered a miniature black hole, which would have a much smaller mass than that of our Sun. But it is possible that miniature black holes may have formed shortly after the “Big Bang”, which is thought to have begun the universe 13.7 billion years ago. Very early in the life of the universe, the rapid expansion of part of the matter may have compressed the matter slowly enough to contract into black holes.
Another division separates black holes that rotate (have an angular momentum) from those that do not.