What Comes After Photographing a Black Hole's Event Horizon? Could we see the Photon Ring?

In 2019 the Event Horizon Telescope (EHT) gave us the first direct image of a black hole. On one hand, the image it produced was rather unimpressive. Just a circular blur of light surrounding a dark central region. On the other hand, subtle characteristics of the image hold tremendous information about the size and rotation of the black hole. Most of the details of the black hole image are blurred by the limits of the EHT. But the next generation EHT should provide a sharper view, and could reveal the dark edge of a black hole’s event horizon.

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How Researchers Produce Sharp Images of a Black Hole

In April of 2019, the Event Horizon Telescope collaboration history made history when it released the first image of a black hole ever taken. This accomplishment was decades in the making and triggered an international media circus. The picture was the result of a technique known as interferometry, where observatories across the world combined light from their telescopes to create a composite image.

This image showed what astrophysicists have predicted for a long time, that extreme gravitational bending causes photons to fall in around the event horizon, contributing to the bright rings that surround them. Last week, on March 18th, a team of researchers from the Harvard-Smithsonian Center for Astrophysics (CfA) announced new research that shows how black hole images could reveal an intricate substructure within them.

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