Radio-astronomy array images distant Universe and finds . . . laser speckle?

April 30, 2013
Astronomers have used the Karl G. Jansky Very Large Array (VLA) to obtain the most detailed image yet of the ancient Universe -- which looks a lot like laser speckle. Is it? (Hint: no, it's not.)
John Wallace 720
Astronomers have used the Karl G. Jansky Very Large Array (VLA) to obtain the most detailed image yet of the ancient Universe -- which looks a lot like laser speckle. Is it? (Hint: no, it's not.) Located at the National Radio Astronomy Observatory (NRAO) in New Mexico, the VLA is one of these incredible scientific instruments that (although its operating wavelengths are a bit long for usual inclusion in Laser Focus World) makes me proud to be a member of the human race. It's made of 27 dishes, each 25 m in diameter, arranged in a Y shape with an adjustable baseline of up to 36 km. Operating at radio wavelengths allows coherent combination of signals, making the array optically similar to a single aperture the size of the baseline. (At optical wavelengths, telescopes can also be coherently combined to form a single aperture -- for example, at the European Southern Observatory's (ESO's) Very Large Telescope Interferometer (VLTI) in Chile -- but the maximum aperture size for the VLTI is about 130 m.)
(Credit: Condon et al., NRAO/AUI/NSF) The image required staring at a small patch of sky for 50 hours with the VLA; for the first time, discrete sources were identified that account for nearly all the radio waves coming from distant galaxies. About 63% of the background radio emission comes from galaxies with active black holes at their cores and the remaining 37% comes from galaxies that are rapidly forming stars. The field of view, in the constellation Draco, encompasses about one-millionth of the whole sky. In that region, the NRAO astronomers identified about 2000 discrete radio-emitting objects. That would indicate, the scientists say, that there are about 2 billion such objects in the whole sky. These are the objects that account for 96% of the background radio emission. However, the researchers point out, the remaining 4% of the radio emission could be coming from as many as 100 billion very faint objects. Who knows -- maybe the same people who believe the Apollo moon landings were actually filmed in a Hollywood studio will fall for the idea that this spectacular image was actually the result of a He-Ne laser beam sent through a diffuser. However, I suspect that the intersection of the two following sets: 1) moon-landing conspiracists, and 2) people who know what laser speckle is, will amount to approximately zero. Source:
About the Author

John Wallace | Senior Technical Editor (1998-2022)

John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.

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