Some rare galaxies exhibit a green glow thanks to the presence of doubly ionized oxygen. This requires UV light from stellar temperatures of 50,000 K and above. Image credit: NASA, ESA, and W. Keel (University of Alabama, Tuscaloosa), of NGC 5972.

Earliest, brightest galaxies shine a ghostly green in surprising new find

Only a few galaxies exhibit this green glow in the nearby Universe. At early times, it’s practically all of the brightest ones.

“The discovery that young galaxies are so unexpectedly bright–if you look for this distinctive green light–will dramatically change and improve the way that we study Galaxy formation throughout the history of the Universe.”
-Matthew Malkan

Here in the nearby Universe, 13.8 billion years since the Big Bang, galaxies come in great varieties.

A great variety of galaxies in color, morphology, age and inherent stellar populations can be seen in this deep-field image. Image credit: NASA, ESA, R. Windhorst, S. Cohen, M. Mechtley, and M. Rutkowski (Arizona State University, Tempe), R. O’Connell (University of Virginia), P. McCarthy (Carnegie Observatories), N. Hathi (University of California, Riverside), R. Ryan (University of California, Davis), H. Yan (Ohio State University), and A. Koekemoer (Space Telescope Science Institute).

Spirals, ellipticals, rings and irregulars, they glow blue, white or red, depending on their stellar populations.

Galaxies undergoing massive bursts of star formation expel large quantities of matter at great speeds. They also glow red covering the whole galaxy, thanks to hydrogen emissions. Image credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA), of the Cigar Galaxy, Messier 82.

The most violent star-forming galaxies and nebulae are so hot they turn red, as ultraviolet radiation ionizes neutral hydrogen.