Using Event Horizon Telescope observations of the center of the galaxy M87, scientists have obtained the first image of a black hole, an accomplishment previously thought of as impossible. The image depicts a bright ring formed from the bending of light due to the intense gravity around the black hole that is 6.5 billion times more massive than the Sun.
It was thought that capturing an image of a black hole was impossible because taking a picture of something from which no light can escape would appear completely black. After working for well over a decade, the team of scientists improved upon an existing radio astronomy technique for high-resolution imaging, using it to detect the silhouette of a black hole.
However, capturing an image of such a distant object still eluded them. Another team formed to take on the challenge an created the Event Horizon Telescope, or the EHT. To capture an image of a black hole, they improved upon a technique that allows the imaging of far-away objects. This is known as Very Long Baseline Interferometry, or VLBI. The larger the diameter of the telescope, the more light it captures. VLBI works by creating an array of smaller telescopes that are synchronized to focus on the same object at the exact same time, actual as a giant virtual telescope. This is an old technique, used to track spacecraft and to image distant cosmic radio sources.
The diameter of the EHT is as large as the distance between the two farthest-apart telescope stations. For EHT, those two stations are at the South Pole and in Spain, creating a diameter that is almost equal to the diameter of the Earth. Each telescope in the array focuses on the black hole and collects data from its location, each telescope providing a portion of the EHT’s full view. The greater the number of telescopes, the better the resolution of the image.
By 2017, the EHT was a collaboration of eight sites around the world, and even more have been added since then. Before the data was collected, the team of scientists had to find a time when the weather was likely to be ideal for viewing at every location. For M87, the 10 days chosen for operation gave a goof four days where each day was clear at each site!
Even though the first picture of a black hole is a noteworthy scientific breakthrough, it has opened new questions for us. For example, scientists are curious about the mechanism by which supermassive black holes emit enormous jets of particles at neat light-speeds.