https://www.universetoday.com/147211/gamma-ray-telescopes-can-measure-the-diameters-of-other-stars/
A high-resolution image of Betelgeuse taken by the ALMA radio telescope. Credit: ALMA (ESO/NAOJ/NRAO)/E. O’Gorman/P. Kervella
With radio interferometry, an array of antenna dishes view the same object from widely separated positions. Waves of light from the object at slightly different times, depending on their location. By correlating the antenna signals, astronomers can create a virtual telescope the size of the array. This is what makes observatories such as the VLA and ALMA so powerful. With radio interferometry, astronomers can even create a virtual telescope the size of Earth, which they used to directly image a black hole.
