By Emily Levesque, University of Washington
The most exciting observation of a black hole happened in 2019, when a team of 347 astronomers announced that they had captured the first actual picture of a black hole. The discovery happened thanks to an incredible collaborative effort on a project known as the Event Horizon Telescope.
Event Horizon Telescope
The Event Horizon Telescope was made up of eight radio observatories scattered across the face of the planet. Using a technique called radio interferometry, astronomers synchronized these observatories to turn the Earth into one giant radio telescope.
In April 2017, this worldwide telescope collected data of the supermassive black hole at the center of a nearby galaxy known as M87. The galaxy was about 53 million light-years away, and the supermassive black hole was 6.5 billion times as massive as our Sun. Still, the edge of the black hole was thought to be barely larger than our solar system.
The picture they took was equivalent to reading the date on a quarter in Washington, DC, while standing in Log Angeles. This first image of a black hole was a revolutionary achievement, confirming many long-held theories of how gravity and black holes should work. It also would not have been possible without the hundreds of people on the team ensuring that every last detail of the telescope and observations were planned and executed to perfection.
Operating as One System
The radio waves emitted by the superheated material around a black hole will bounce right off of water molecules in our atmosphere. This means that to observe them we need to use telescopes built in some of the driest places in the world, like the Atacama Desert in Chile, southern Arizona, the summit of Mauna Kea in Hawaii, and the desert-like climate of the South Pole.
The telescopes used in the Event Horizon telescope were already in these dry and remote locations, but they weren’t originally designed to work together: each one was built separately and spent most of its time operating as an independent observatory. It took years for team members to retrofit each individual telescope with customized equipment so that the Event Horizon Telescope could operate as one system.
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Facing Unique Challenges
Each site in the array also has its own quirks. One telescope in Hawaii observes from under a Gore-Tex shroud to protect it from wind, blowing sand, and even bird droppings. A Spanish telescope in the array is equipped with its own de-icing system so that it can quickly recover from mountain storms. The Atacama Large Millimeter/Submillimeter Array in Chile is at an altitude of just over 16,000 feet; astronomers and engineers working there need supplemental oxygen to work safely in the thin air.
For interferometry to work we also need to know exactly when and where each piece of data is captured. This means equipping each telescope with an atomic clock and tracking its location with military-grade GPS. Keeping track of where a large telescope is may sound like a simple job, but the very ground they’re built on will sometimes move. Hawaii and Chile are famously earthquake-prone, and the South Pole Telescope is built on the Antarctic ice sheet, which drifts more than 30 feet every year.
Waiting for Perfect Weather
Getting all eight telescopes to observe the supermassive black hole in M87 at the same time also meant waiting for perfect weather at eight different sites around the globe. Team members around the world had to wait anxiously for a go/no-go decision every night, with thunderstorms in Mexico and windy weather in Arizona grinding worldwide observations to a halt for two days in the middle of the team’s work.
Finally, data from the different telescopes can’t just be passed along by email or uploaded to a server. By the time the telescopes were done observing M87’s supermassive black hole they had generated five petabytes of data.
Processing the Data
Processing the data from all eight sites meant shipping the hard drives around the world. Even moving the drives was easier said than done—the observations happened during Antarctic winter, when there are no flights to or from the continent, so the South Pole data had to wait until November before it could be flown back to one of the team’s supercomputers.
At the supercomputers, astronomers and computer scientists on the team then spent months perfecting techniques for analyzing and combining the data. In the end, it took several hundred heroes of astronomy—physicists, engineers, computer scientists, astronomers, and the many people who operate and run the eight telescopes around the world—to capture humanity’s first groundbreaking glimpse of a black hole.
Common Questions about How Astronomers Achieved the First Glimpse of a Black Hole
The Event Horizon Telescope was made up of eight radio observatories scattered across the face of the planet. Using a technique called radio interferometry, astronomers synchronized these observatories to turn the Earth into one giant radio telescope.
The radio waves emitted by the superheated material around a black hole will bounce right off of water molecules in our atmosphere. This is why to observe them, we need to use telescopes built in some of the driest places in the world, like the Atacama Desert in Chile, southern Arizona, the summit of Mauna Kea in Hawaii, and the desert-like climate of the South Pole.
For interferometry to work we need to know exactly when and where each piece of data is captured. This means equipping each telescope with an atomic clock and tracking its location with military-grade GPS.
