Farther from zero corresponds to a larger separation and, thus, a finer resolution. The x-axis is east-west the y-axis is north-south. This graph plots the distance between the telescopes divided by the wavelength observed. Each forms a pair with the others, their baselines drawn in red. As the world turns, different telescopes come into view. On the left is Earth as seen by M87’s black hole. The animations below by graduate student Daniel Palumbo (Harvard) show how the Event Horizon Telescope’s VLBI network works. That’s why the Event Horizon Telescope isn’t just two scopes at opposite ends of the world: They need a variety of separations, or baselines, in order to fill in the image. The solution is a bunch of telescopes with different separations, which enable you to mix and match the pairs and detect structures of various sizes and orientations. In order to reconstruct the image, you need a detailed understanding of how the radio waves are augmenting or canceling one another out as they travel to the dishes. Account for that delay, then carefully add the data together, and you can measure the object's structure with the resolution you’d have from a telescope that is the size of the distance between the two dishes.īut when observing something with structure on a variety of scales, things get complicated - it’s like having a flock of ducks cavorting in the pond, their waves interacting and changing the pattern in complex ways. The two telescopes will catch a slightly different part of each wavefront. Light comes from the object as a wavefront, like ripples in a pond created by splashing ducks. The basic principle of interferometry is this: take two telescopes, separated by some distance, and observe an object simultaneously with both telescopes. But no one before has ever achieved VLBI with a frequency able to so stunningly invade a galaxy’s innermost sanctum. VLBI is actually not new radio astronomers have been using it for decades. The answer is a technique called very long baseline interferometry. The dishes observed simultaneously, effectively acting as a virtual, planet-size dish, giving them a resolving power equivalent to being able to see a hydrogen atom at arm’s length.īut how do you build a virtual telescope? To create this image, an international team combined observations from radio telescopes spread across the globe, from Hawai‘i to Spain and Arizona to Chile. The shadow is wreathed by the light from hot gas just outside the black hole, which whirls around the invisible beauty. On April 10th, scientists delighted the world by unveiling an image of the black hole at the center of the distant galaxy M87.

Solid baselines indicate telescope pairs that could see M87's black hole simultaneously dashed lines indicate telescope pairs used to observe a different, calibration source.Įvent Horizon Telescope Collaboration / Astrophysical Journal Letters, 875(2019) L1 / CC BY 3.0 The Event Horizon Telescope April 2017 observing campaign comprised eight telescopes in six geographic locations.

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