This soon-to-be famous image, courtesy of the Event Horizon Telescope (EHT), is our first picture of the black hole that sits inside Messier 87 (M87), a galaxy located 53 million light-years from Earth.
This bright image was revealed by researchers at a number of worldwide press conferences today. It shows visual evidence of the event horizon of a black hole and allow us to see something previously thought to be invisible.
“History books will be divided into the time before the image and after the image,” said Michael Kramer from the Max Planck Institute for Radio Astronomy in one of the press conferences.
But how do you take a picture of something that doesn’t radiate light? Well, rather than looking directly at the black hole, the EHT looks at gas surrounding it to take an image of its shadow. Specifically, researchers looked at the event horizon, the limit beyond which light can no longer escape the intense gravity of the black hole. This gas in this area heats up to billions of degrees, creating a silhouette whose shape should be able to be predicted by Einstein’s theory of relativity.
That shadow is revealed in the center of today’s picture.
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The image was created using radio astronomy. Most radio astronomy is done using large dishes that capture radio waves hitting Earth. But creating an image of the black hole required a telescope quite a bit larger. Researchers needed one the size of our planet.
That’s why the Event Horizon Telescope combined measurements from radio observatories on four separate continents. The array is currently made up of sites in North America, South America, Europe, and Antarctica, with other locations being included over its life cycle. When all dishes take measurements at the same time, they can be combined into a conglomeration of data, similar to what’s taken on a smaller scale in radio dishes. (Check out a great explainer video that goes into more detail here.)
The information used to make the image revealed today comes primarily from data taken in April 2017. Over the past two years, researchers from around the world have worked to turn that information into the clearest image possible by synching up the measurements taken concurrently around the world. In 2018, an observatory in Chile was added to help create a clearer photo, after the initial results that came back were a tad foggy.
The reveal of the image is a huge milestone for the study of black holes. “While we confirmed the existence of black holes and studied their properties in so many ways, nothing beats a direct observation,” University of Southern California professor Clifford Johnson told MIT Technology Review in advance of the announcement. “It’s rather like seeing the shots fired as well as the smoking gun.”