Astronomers using the Five-hundred-meter Aperture Spherical Telescope (FAST) have discovered a 2-million-light-year-wide cloud of atomic hydrogen around Stephan’s Quintet, a famous compact group of galaxies discovered in 1887. Contour map of the integrated atomic hydrogen emission in the vicinity of Stephan’s Quintet overlaid on the composite color image. Image credit: NASA / ESA / CSA / STScI. “Atomic hydrogen is the least bound component of...
