How an Earth-Sized Telescope Images Supermassive Black Holes

Ziri Younsi, a member of the Event Horizon Telescope collaboration, explains how scientists managed to photograph a black hole across 55 million light years.
July 27, 2021, 1:00pm
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Black holes are so massive that they do not allow anything, even light, to escape from beyond the event horizons that border them. As a result, these objects are extremely difficult to directly image, because they are essentially invisible to most light-based telescopes. 

That’s why the first image ever snapped of a black hole made such a splash when it was released in 2019. Captured by the Event Horizon Telescope (EHT) collaboration, the haunting picture reveals the supermassive black hole at the center of Messier 87, a galaxy located 55 million light years away. The EHT, a network of radio telescopes that spans the globe, provided the exceptional resolution needed to image such a distant and exotic object.

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“This famous image that we first saw in April 2019 was actually the combined efforts of eight radio telescopes spread all around the world, including even in the South Pole,” said EHT team member Ziri Younsi, an astrophysicist and UKRI Stephen Hawking Fellow at University College London's Mullard Space Science Laboratory, in a new episode of Motherboard’s “Space Show.” 

“It is precisely because of this scale—because [the EHT] is Earth-sized—that we can achieve the resolutions that we need to resolve a black hole,” he continued. “Even though the supermassive black hole in the galaxy Messier 87 that we saw is an enormous black hole, it's actually still very very far away, so it's angular size on the sky is absolutely miniscule. It's an unprecedented technological feat, really, to be able to achieve the kind of resolutions that we achieved as a collaboration to resolve it in the first place.”

Indeed, the EHT’s resolving power is equivalent to spotting an orange on the Moon with the naked eye, or seeing the individual atoms in your hands at arm’s length. Since its captivating debut image, the collaboration has turned the telescope’s sights to other tantalizing targets, such as Centaurus A, the nearest active galaxy to the Milky Way. The team also plans to use its Earth-sized instrument to study the supermassive black hole at the center of our own galaxy.

The EHT’s amazing capacity to stare deep into the abyss of black holes and other extreme objects not only makes for exciting new visuals, it can also shed light on some of the most fundamental mysteries of the universe, such as the nature of gravity and the evolution of the universe.

“Black holes have the strongest gravitational fields in the universe,” Younsi said. “If you can start to understand more about what's going on about gravity in that regime, then you understand more about what space and time really mean, and you understand more about what it is to have cosmic expansion, and where we come from.”

“It really touches at the heart of basic human understanding, or what governs the universe,” he added.