The black hole and its shadow have been unveiled by the Event Horizon Telescope, an international collaboration of over 200 researchers from Africa, Asia, Europe, North and South America, including experts from UCL’s Mullard Space Science Laboratory.
Located 55 million light-years away in the Messier 87 (M87) galaxy, the black hole is said to measure just under 40 billion kilometres across, or approximately three million times the diameter of the Earth. According to UCL, its mass is 6.5 billion times that of the Sun.
The Event Horizon Telescope (EHT) was established to image a black hole by linking eight ground-based radio telescopes globally to make an Earth-sized virtual telescope with unprecedented sensitivity and resolution.
Following decades of observational, technical and theoretical work, the breakthrough was announced in six papers published in a special issue of The Astrophysical Journal Letters.
“We have accomplished something many thought impossible by imaging the shadow of a black hole and it provides the strongest evidence to date that such evasive and enigmatic entities do indeed exist. It’s the closest we can get to imaging a black hole, which is an object with such a strong a gravitational field that no light or matter can escape,” said Dr Ziri Younsi, UCL Mullard Space Science Laboratory.
With enormous masses but extremely compact sizes, black holes dramatically affect their environment by warping spacetime and super-heating any surrounding material.
"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," said chair of the EHT Science Council Professor Heino Falcke, of Radboud University in the Netherlands. "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."
According to UCL, M87’s black hole is around 2.5 times smaller than the shadow it casts, which is surrounded by a ring-like structure with features that closely matched theoretical models.
"Once we were sure we had imaged the shadow, we could compare our observations to extensive computer models that include the physics of warped space, superheated matter and strong magnetic fields. Many of the features of the observed image match our theoretical understanding surprisingly well," said Dr Paul T.P. Ho, EHT Board member and Director of the East Asian Observatory. “This makes us confident about the interpretation of our observations, including our estimation of the black hole’s mass."
The observations were made in 2017 using very-long-baseline interferometry which synchronises telescopes around the world and exploits Earth’s rotation to form one planet-sized telescope.
The telescopes are located in volcanoes in Hawai’i and Mexico, mountains in Arizona and in the Spanish Sierra Nevada, the Chilean Atacama Desert, and Antarctica.
Whilst not physically connected, the telescoped synchronise their recorded data with atomic clocks - hydrogen masers - which precisely time their observations. According to EHT, these observations were collected at a wavelength of 1.3mm during 2017. Each telescope produced roughly 350 terabytes of data per day, which was stored on helium-filled hard drives. These data were flown to highly specialised supercomputers - called correlators — at the Max Planck Institute for Radio Astronomy and MIT Haystack Observatory to be combined. They were then converted into an image with computational tools developed by the collaboration.
"Breakthroughs in technology, connections between the world's best radio observatories, and innovative algorithms all came together to open an entirely new window on black holes and the event horizon," said EHT project director Professor Sheperd S. Doeleman, Center for Astrophysics, Harvard & Smithsonian.
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