How to hunt for a black hole with a telescope the size of Earth

By Davide Castelvecchi

Here’s how to catch a black hole. First, spend many years enlisting eight of the top radio observatories across four continents to join forces for an unprecedented hunt. Next, coordinate plans so that those observatories will simultaneously turn their attention to the same patches of sky for several days. Then, collect observations at a scale never before attempted in science — generating 2 petabytes of data each night.

This is the audacious plan for next month’s trial of the Event Horizon Telescope (EHT), a team-up of radio telescopes stationed across the globe to create a virtual observatory nearly as big as Earth. And researchers hope that when they sift through the mountain of data, they will capture the first details ever recorded of the black hole at the centre of the Milky Way, as well as pictures of a much larger one in the more distant galaxy M87.

The reason this effort takes so much astronomical firepower is that these black holes are so far from Earth that they should appear about as big as a bagel on the surface of the Moon, requiring a resolution more than 1,000 times better than that of the Hubble Space Telescope. But even if researchers can nab just a few, blurry pixels, that could have a big impact on fundamental physics, astrophysics and cosmology. The EHT aims to close in on each black hole’s event horizon, the surface beyond which gravity is so strong that nothing that crosses it can ever climb back out. By capturing images of what happens outside this zone, scientists will be able to put Einstein’s general theory of relativity to one of its most stringent tests so far. The images could also help to explain how some supermassive black holes produce spectacularly energetic jets and rule over their respective galaxies and beyond.

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