The gravity of the first ever image of a black hole, explained

Astronomers across the world joined forces, and telescopes, to take the first ever image of a black hole. The Event Horizon Telescope (EHT), a network of eight different telescopes, captured the picture of a massive black hole that is three million times the size of the Earth.

EHT says the black hole is located in a distant galaxy, Messier 87 [1], commonly known as M87; it is 55 million light years away from the Earth. M87 is an elliptical galaxy in the Virgo cluster.

“The image shows a bright ring formed as light bends in the intense gravity around a black hole that is 6.5 billion times more massive than the sun,” says the EHT.

The circle of light around the black shadow is created by superheated gas falling into the black hole. The light emitted in the process is brighter than billions of other stars in the galaxy combined.

The image is the strongest evidence of the existence of black holes, which Einstein’s theory of relativity first predicted in 1905, says the EHT. This historic development even got Google to make a doodle for it.

The breakthrough was announced in the journal The Astrophysical Journal Letters. The imaging project started in 2017 and cost about $50 million.

How the first ever image of a black hole was taken

The Event Horizon ‘Scope says that over 200 researchers and eight observatories participated in the image capturing process—ALMA Chile, SMA Hawaii, SPT South Pole, SMT Arizona, PV Spain, JCMT Hawaii, LMY Mexico, and APEX Chile.

These eight telescopes perched at high altitudes were linked together to form an Earth-sized virtual telescope that had an extremely high resolution and sensitivity. In fact, this virtual telescope had a clear enough resolution to read a newspaper in New York City from a cafe in Paris.

Scientists used a very long-baseline interferometry (VLBI) method that synchronised the telescopes while the planet was rotating to observe the black hole at a wavelength of 1.3 mm.

The telescopes picked up the glowing X-ray light that can be seen as the “event horizon”.

The National Science Foundation explains that close to the black hole are intense gravitational pulls bend photons and particles from their original paths. These particles then make up the event horizon or ring of light surround the dark centre.

“Multiple calibration and imaging methods have revealed a ring-like structure with a dark central region—the black hole’s shadow—that persisted over multiple independent EHT observations,” says EHT.

Simply put, the signals received by the telescopes were fed to powerful computers that then turned the data into an image.

The image captured looks very similar to scientific and pop culture re-imaginings. Director of the East Asian Observatory Paul T.P. Ho said the observed image matches our theoretical understanding of black holes well.

Falcke says, “It is remarkable that the image we observe is so similar to that which we obtain from our theoretical calculations. So far, it looks like Einstein is correct once again.”

What is a black hole?

EHT explains that black holes are “cosmic objects with enormous masses but extremely compact sizes. The presence of these objects affects their environment in extreme ways, warping spacetime and super-heating any surrounding material.”

Einstein predicted that if a disc of glowing gas were to find its way to a black hole, the dark area would look like a shadow.

However, prior to this image, scientists had never seen such a sight before because black holes are either extremely compact or too far away or both, making them difficult to directly observe.

Who is Katie Bouman?

Twenty-nine-year-old Katie Bouman’s efforts were crucial to this incredible stride in space research. She studied computer science and artificial intelligence at the Massachusetts Institute of Technology (MIT).

Three years ago, Bouman had developed one of the key imaging algorithms that was used to piece together the data from the telescopes to create the black hole image.

In 2016, Bouman was one of the lead researchers at MIT who managed to code an algorithm that could connect the required data. MIT explains that because black holes are so far away, one would need a 10,000-kilometre telescope to capture an image of one.

However, this is not practical because the Earth’s diameter is less than 13,000 kilometres. To overcome this obstacle, EHT coordinated with telescopes at various locations to create a large enough field of vision.

Even so, there were large gaps in the data and a lot of atmospheric noise to filter out. This is where Bouman’s algorithm, CHIRP (Continuous High-resolution Image Reconstruction using Patch priors), comes in.

However, the data still needed to be verified by a number of different, independent teams to see if all the images they each came up with corresponded. Bouman also led the testing and imaging teams that analysed the signals.

“We developed ways to generate synthetic data and used different algorithms and tested blindly to see if we can recover an image,” Bouman told CNN.

An image of Bouman posing with the hard drives for this project is being likened to one of MIT computer scientist Margaret Hamilton standing with a large stack of books containing code she wrote for on-board moon mission.

Bouman will begin her tenure as an assistant professor at the California Institute of Technology later in August.

Historic achievement

Nothing, not even light, can escape the strong gravitational pull of a black hole. However, with the international cooperation between all eight observatories and hundreds of researchers, something people once thought was impossible is now a reality.

The East Asian Observatory was one of EHT’s partners and represented China, Japan, Korea, Taiwan, Vietnam, Thailand, Malaysia, India, and Indonesia.

“We have achieved something presumed to be impossible just a generation ago,” said EHT Project Director Sheperd S. Doeleman.

Rhea Arora is a Staff Writer at Qrius

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