Network of eight radio telescopes around the world records revolutionary image
By
Hannah Devlin
Astronomers have captured the first image of a black hole, heralding a revolution in our understanding of the universe’s most enigmatic objects.
The picture shows a halo of dust and gas, tracing the outline of a colossal black hole, at the heart of the Messier 87 galaxy, 55m light years from Earth.
Quick guide
What are black holes?
Black holes were first predicted by Einstein’s theory of general relativity, which reimagined gravity as the warping of space and time by matter and energy.
The equations predicted that, beyond a certain threshold, when too much matter or energy is concentrated in one place, space and time collapse, leaving behind a sinkhole through which light and matter can enter but not escape.
At first these were thought to be mathematical oddities, rather than real astronomical objects, but in the past century overwhelming evidence has confirmed that black holes are out there.
The edge of the black hole is defined by its so-called event horizon. This is the point at which escaping would require something to travel at faster than the speed of light – which as far as we know nothing does – so it is the point of no return.
Black holes are surrounded by an accretion disk of dust and gas, orbiting at close to the speed of light. A lot of this material is destined for oblivion, although some of it is ejected as powerful jets of radiation.
The black hole itself – a cosmic trapdoor from which neither light nor matter can escape – is unseeable. But the latest observations take astronomers right to its threshold for the first time, illuminating the event horizon beyond which all known physical laws collapse.
The breakthrough image was captured by the Event Horizon Telescope (EHT), a network of eight radio telescopes spanning locations from Antarctica to Spain and Chile, in an effort involving more than 200 scientists.
…
France Córdova, director of the US National Science Foundation and an astrophysicist, said that the image, which she had only seen as it was unveiled at the press briefing she was chairing, had brought tears to her eyes. “We have been studying black holes for so long that sometimes it’s easy to forget that none of us has seen one,” she said. “This will leave an imprint on people’s memories.”
...
The EHT picks up radiation emitted by particles within the disc that are heated to billions of degrees as they swirl around the black hole at close to the speed of light, before vanishing down the plughole.
The halo’s crescent-like appearance in the image is because the particles in the side of the disc rotating towards Earth are flung towards us faster and so appear brighter. The dark shadow within marks the edge of the event horizon, the point of no return, beyond which no light or matter can travel fast enough to escape the inexorable gravitational pull of the black hole.
Black holes were first predicted by
Einstein’s theory of relativity – although Einstein himself was sceptical that they actually existed. Since then, astronomers have accumulated overwhelming evidence that these cosmic sinkholes are out there, including
recent detection of gravitational wavesthat ripple across the cosmos when pairs of them collide.
But black holes are so small, dark and distant that observing them directly requires a telescope with a resolution equivalent to being able to see a bagel on the moon. This was once thought to be an insurmountable challenge.
The EHT achieved the necessary firepower by combining data from eight of the world’s leading radio observatories, including the Atacama Large Millimetre Array (Alma) in Chile and the South Pole Telescope, creating an effective telescope the size of the Earth.
When observations were launched in 2017, the EHT had two primary targets. First was
Sagittarius A*, the black hole at the centre of the Milky Way, which has a mass of about 4m suns. The second target, which yielded the image, was a supermassive black hole in the galaxy M87, into which the equivalent of 6bn suns of light and matter has disappeared.
The collaboration is still working on producing an image of the Milky Way’s black hole. “We hope to get that very soon,” said Doeleman.
...
