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Will the first recording be presented tomorrow?

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In April 2019, the Event Horizon Telescope Collaboration presented this image. It is the first visual evidence of a supermassive black hole. (Archive photo) © Event Horizon Telescope (EHT)/dpa

At the center of the Milky Way lurks the supermassive black hole Sagittarius A*. The first photo of it could be shown at a press conference.

Garching – When the Event Horizon Telescope (EHT) Collaboration held a press conference in April 2019, the researchers involved presented a groundbreaking scientific achievement: They had photographed the shadow of a black hole for the first time and thus visible evidence of a supermassive black hole rendered. The picture went around the world and suddenly caused a great deal of interest in black holes. Now there is another invitation to a press conference of the EHT, where “groundbreaking results for the Milky Way” are to be presented. Just like in 2019, there will be multiple press conferences around the world at the same time. Much more is not known so far.

But in the scientific community there is a guess as to what the EHT will present this time: Is it the first image or even a film of Sagittarius A*, the supermassive black hole at the center of the Milky Way? It is possible – experts had already suspected in 2019 that an image of Sagittarius A* would be presented. However, the researchers then presented an image of the black hole at the center of the Messier 87 galaxy.

Event Horizon Telescope: Did it photograph the black hole at the center of the Milky Way?

But how is it even possible for the Event Horizon Telescope to photograph a black hole? Supermassive black holes are found at the center of most galaxies and are characterized by one thing: they devour everything that gets too close. Matter, once it has crossed the event horizon, falls into the black hole from which nothing comes out – not even light. Something that itself swallows light is actually impossible to photograph. What’s more, black holes are far away – the black hole captured in 2019 is about 55 million light-years from Earth, the black hole at the center of the Milky Way is about 26,000 light-years away.

supermassive black hole
center of the Milky Way
4.3 million solar masses
about 26,000 light years

In order to still be able to photograph black holes, the EHT uses a special technique: Very Long Baseline Interferometry (VLBI). Several radio telescopes distributed all over the world are synchronized and used simultaneously to observe a selected object. When the first photo of a black hole was published, the researchers involved explained that they could read a newspaper in New York from Paris with the resulting resolution of their huge, earth-spanning telescope.

Event Horizon Telescope (EHT): How do you photograph a black hole that swallows light?

But that still doesn’t explain how the researchers can photograph an object that swallows light. You have to know that supermassive black holes are usually surrounded by what is known as an accretion disk. This consists of matter that has been attracted to the black hole but has not yet crossed the event horizon. This accretion disk surrounds the black hole, the gas inside it is hot and glows – which the researchers used for their purposes in 2019. As Heino Falcke from the EHT explained in 2019: “When a black hole plunges into a bright region like a disk of glowing gas, we expect it to produce a dark region that resembles a shadow.”

And indeed: The Event Horizon Telescope was able to photograph the ring-like structure with a dark center – the shadow of the black hole. Eight telescopes were involved in the observation at the time – they were in Hawaii, Mexico, Arizona and the Sierra Nevada, in the Chilean Atacama Desert and even in Antarctica. The observations resulted in petabytes of raw data that were processed by supercomputers, including those at the Max Planck Institute for Radio Astronomy in Bonn.

“We have achieved what was thought impossible just a generation ago.”

Photographing a black hole was thought impossible a generation ago

“We have achieved something that was thought impossible a generation ago,” said EHT researcher Sheperd S. Doeleman in a 2019 press release. “Breakthroughs in technology, connections between the world’s best radio observatories, and innovative algorithms have opened up a whole new window for us on black holes and the event horizon.”

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Will the Event Horizon Telescope provide a view of the black hole at the center of the Milky Way this time? It’s possible – but it’s also possible that the Event Horizon Telescope Collaboration has a completely different surprise in store for observers. (tab)

#recording #presented #tomorrow

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