D14 Radio astronomy

Topic

Radio astronomy observes wavelengths millions of times longer than those of visible light.

The angular resolution of an individual antenna, like that of any optical system, improves with a larger aperture and shorter wavelength; But since radio waves are so long, matching the resolution of an optical telescope with a single antenna would require building an antenna of an impractical size.

Interferometry resolves this same limitation in the same way that optical interferometry already resolves it, and extending the baselines of these antennas to continental scales makes it possible to achieve such fine angular resolutions that made it possible to obtain, for the first time, an image of the shadow of a black hole. Furthermore, combining dozens of antennas separated by several kilometers further refines that resolution and sensitivity to millimeter wavelengths.

Aperture synthesis takes advantage of the Earth's own rotation to change, throughout the same observation, the relative geometry that exists between the array's antennas, and it is precisely this change in geometry that completes the information necessary to reconstruct an image that a fixed antenna array would never be able to capture on its own. Thus, from the extremely long wavelengths with which this document begins to that aperture synthesis with which it ends, through the limited angular resolution of a single antenna and the interferometry of continental baselines, radio astronomy causes waves that are too long to be resolved with a single instrument to end up revealing, combined between many instruments at the same time, even the very shadow of a black hole.

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