We’ve never seen an event horizon, nor directly imaged a black hole. Thanks to a worldwide effort, victory may at last be in sight.
“Never look down to test the ground before taking your next step; only he who keeps his eye fixed on the far horizon will find the right road.”
Perhaps gravity’s oddest prediction is the existence of black holes: regions of space where gravity is so strong that nothing, not even light, can escape.
Only through gravitational effects, such as by influencing stars, have they ever been seen.
X-ray signatures can locate and be used to weigh black holes as well, but that evidence is indirect.
Actively merging black holes can be detected through their gravitational waves, but cannot produce direct images.
But all of that is about to change, with the impending activation of the Event Horizon Telescope.
Instead of a single telescope, 15-to-20 radio telescopes are arrayed across the globe, observing the same target simultaneously.
With up to 12,000 kilometers separating the most distant telescopes, objects as small as 15 microarcseconds (μas) can be resolved: the size of a fly on the Moon.
The largest black hole as viewed from Earth is Sagittarius A*: at the center of the Milky Way.
Despite being 26,000 light years away, its mass of 4 million Suns gives it an angular size of 37 μas.
The Event Horizon Telescope turns on this week.
For the first time ever, we will directly image a black hole, testing whether event horizons truly exist.
Mostly Mute Monday tells the story of an astronomical object or phenomenon in images, visuals and no more than 200 words.Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.