The gas falling into black holes emits light across the electromagnetic spectrum, but the hottest, most energetic gas, which is swirling closest to a black hole's event horizon, can be seen in X-ray light. While the Event Horizon Telescope is observing black holes in radio wavelengths, the other frontier of black hole astronomy is in the X-ray regime. "That would be the most extreme general relativistic effect detected so far," he added. If black holes do produce shadows, the Event Horizon Telescope should be able to see one at Sagittarius A* within the next few years, said Dexter, the University of California, Berkeley, theorist. If event horizons exist, general relativity also predicts black holes will have shadows, or darkened regions where light has been swallowed. An event horizon is a theorized boundary around a black hole that marks the "point of no return" where matter and even light can't escape. One question scientists hope to answer is whether black holes really have event horizons, as predicted by general relativity. "That's an area where the gravity is so strong that light is bent and the structures you see are dominated by strong gravity, where you absolutely need Einstein to understand what you're seeing. "The Event Horizon Telescope is going to look at emission at the edge of the black hole itself," Doeleman said. (Image credit: Dan Marrone/University of Arizona ) At the center of the detector is a small rectangular hole to collect light. That means we can average our data over those time periods because they will all have kept time very perfectly."Ī detector built for the South Pole Telescope will enable it to take part in the Event Horizon Telescope project, which will combine data from observatories around the world to image the immediate environment of a black hole for the first time. It creates very perfect oscillations for a short time period. "It creates a low-frequency signal that through careful design you can make a very precise oscillator. "We use this property of the structure of the hydrogen atom to create a fundamental time reference for us that transitions between two states of the electron in a hydrogen atom," Marrone said. The researchers have been using atomic clocks made of what's called hydrogen masers to keep time to an accuracy of about a trillionth of a second per second. "We had to prove you could keep time well enough at all the stations, and that the detectors at all the telescopes were good enough, that when you multiply the two signals from two telescopes you wouldn’t get just noise," said Dan Marrone, an astronomer at the University of Arizona's Steward Observatory who's building a receiver to enable the South Pole Telescope to join the project. Using this technique, known as Very Long Baseline Interferometry (VLBI), an international group of astronomers has now measured the launch point of a relativistic jet of that is powered by a supermassive black hole at the heart of a galaxy called M87. The Event Horizon Telescope (EHT) is a growing array of radio dishes that combine to form a virtual Earth-sized telescope with magnifying power more than 2000 times that of the Hubble Space Telescope. This short-wavelength light is what's needed to achieve the angular resolution required to measure and image black holes. Very long baseline interferometry has been used for about 50 years, but never before at such a high frequency, or short wavelength, of light. "Whenever you change something by an order of magnitude, wonderful things happen." "It's going to increase the sensitivity of the Event Horizon Telescope by a factor of 10," Doeleman said. The lens becomes a supercomputer here at MIT."Ī major improvement to the Event Horizon Telescope's imaging ability will come when the 64 radio dishes of the ALMA (Atacama Large Millimeter/submillimeter Array) observatory in Chile join the project in the next few years. The way VLBI works is, we have to freeze the light, capture it, record it perfectly faithfully on the recording system, then shift the data back to a central supercomputer, which compares the light from California and Hawaii and the other locations, and synthesizes it. "In a typical telescope, light bounces off a precisely curved surface and all the light gets focused into a focal plane. "If you have telescopes around the world you can make a virtual Earth-sized telescope," said Shep Doeleman, an astronomer at MIT's Haystack Observatory in Massachusetts who's leading the Event Horizon Telescope project. In VLBI, a supercomputer acts as a giant telescope lens, in effect. To accomplish such fine resolution, the project takes advantage of a technique called very long baseline interferometry (VLBI).
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