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
John Wallace 720
John Wallace 720
John Wallace 720
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: http://www.nrao.edu/pr/2013/vladeep/
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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