The event horizon telescope (EHT) uses multiple radio dishes to form a 10,000-kilometer-wide “virtual” telescope powerful enough to detect a golf ball on the Moon.
An image of the black hole Sagittarius A*. Image: EHT
The event horizon telescope (EHT) is a network of radio disks designed to detect light as matter disappears in a black hole. The EHT is one of many notable astronomy projects that have expanded human observations of the universe in recent years. On May 12, scientists released the first image of a supermassive black hole at the center of the Milky Way, called Sagittarius A*. So how does EHT work?
The EHT consists of a unique set of antennas around the world, forming a virtual telescope roughly the size of Earth (about 10,000 km). The radio disk network was tuned towards the Milky Way and became operational in 2015 with the participation of 80 different astronomy institutes. In 2019, EHT shared the first image of the black hole M87* in a galaxy far away from us.
On May 12, an international team of astronomers revealed the first image of the supermassive black hole Sagittarius A*, 26,000 light-years from Earth and with a mass equivalent to 4 million Suns. In theory, observing a black hole is impossible because light cannot escape it. But EHT fixed this problem. The network records flashes of light that are produced when matter such as planets, debris or anything that comes too close, is sucked into the outer edge of a black hole, the event horizon.
“We were able to detect the silhouette of a black hole on a background of glowing gas and dust,” said researcher Frederic Geth of the Franco-German Institute of Millimeter Radio Astronomy.
The swirling cloud of matter around the black hole can only be observed using a precise band of radio frequencies called millimeter waves and using a much larger radio telescope like a TV satellite dish. The device needed to be massive to detect weak radio signals emanating from an object at a great distance from Earth. But no radio telescope with current technology has high enough resolution.
So astronomers use interferometry, linking pairs of radio antennas pointed at the same object in the sky to create “virtual” telescopes called interferometers. This combination can observe details like a camera’s zoom lens. The EHT project went further, using radio telescopes at eight observatories around the world, from the US to Europe and from Greenland to Antarctica, to create a new, much more powerful telescope. This technique is called very long baseline interference (VLBI).
While the Earth rotates, different telescopes can pick up slightly different light waves emitted by the matter surrounding the black hole. Researchers can combine models to create a complete image. The signal received at each antenna needs to match, even when halfway around the world, so each facility is equipped with an atomic clock.
The success of the EHT in detecting M87* and Sagittarius A* provides further evidence of a supermassive black hole, a major step forward in strengthening hypotheses about the structure of the universe. Black holes are the most extreme and chaotic environment that has ever existed. But thanks to EHT, researchers can better understand this mysterious object.
An Khang (According to Phys.org)
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