What does a black hole look like? We’ve seen stunning depictions of the cosmic phenomenon in movies such as Interstellar, but we’ve never seen a black hole before. Scientists think they know what they look like, but a real photo of one has eluded us. But that could soon change.
Researchers from MIT created a new algorithm (Continuous High-resolution Image Reconstruction using Patch priors, or CHIRP) that might just produce the first image of a black hole. So, what would the algorithm do? It would stitch together data collected from radio telescopes all around the globe.
Katie Bouman, an MIT graduate student and leader of the development of the new algorithm, talked up the advantages of radio telescopes.
“Radio wavelengths come with a lot of advantages,” says Bouman. “Just like how radio frequencies will go through walls, they pierce through galactic dust. We would never be able to see into the center of our galaxy in visible wavelengths because there’s too much stuff in between.”
But radio telescopes aren’t the Hubble. You won’t see incredible, colorful images from them. Take the largest single radio-telescope dish in the world at 1,000 feet in diameter. A regulartypical backyard optical telescope could still take a better image of the moon.
The 1,000-foot diameter Arecibo Radio Telescope in Puerto Rico.
Why? It’s because radio waves are much longer than optical waves. That’s why you usually see radio telescopes bundled together in arrays.
Bouman goes on to explain the issue with imaging a black hole.
“A black hole is very, very far away and very compact,” Bouman says. “[Taking a picture of the black hole in the center of the Milky Way galaxy is] equivalent to taking an image of a grapefruit on the moon, but with a radio telescope. To image something this small means that we would need a telescope with a 10,000-kilometer diameter, which is not practical, because the diameter of the Earth is not even 13,000 kilometers.”
To address this, astronomers use a technique called interferometry. Basically, they collect data from the same object from radio telescopes all around the world. And then combine all that data. By taking the two telescopes furthest away from each other, they create a telescope with a “diameter” of that distance.
One issue that pops up is Earth’s atmosphere can slow radio waves down. This can throw off the differences in arrival time from one telescope to the other. And for a technique that requires precise data, that’s a problem. MIT’s algorithm takes measurements from three telescopes and multiplies them. The extra delays caused by Earth’s atmosphere are canceled out. It requires a bit more manpower, but the bump in precision would be worth it.
Right now, the project (called Event Horizon Telescope) has six observatories on board. They hope more will join. More data means more precise results.
Bouman will present her new algorithm at the Computer Vision and Pattern Recognition conference in June.
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