Galaxies normally glow white, with slight variations in color. Galaxies with a lot of hydrogen gas, which signal young galaxies and star formation, can look slightly pink, for instance. Others with red stars can have red, orange or yellow tints.
Green galaxies are much more rare, because they require very specific conditions.
A supernovae to spawn oxygen formation.
Stars that burn at around 50,000 degrees Kelvin, approaching temperatures of the hottest known stars in the universe. The hot stars can then ionize the oxygen clouds two times to create a green-glowing O++ “doubly-ionized” cloud in the green light spectrum.
Usually, those stars only exist in very small “dwarf galaxies,” with one of the most common types being “green pea galaxies.”
Malkan and his team pored through the Subaru Deep Field, created by the 8.2 meter (27-foot) Subaru Telescope in Hawaii, and found that all the small galaxies were “surprisingly strong emitters” of green light. Furthermore, the early universe (under 2 billion years old and 70 times more dense than today) is made up mostly from such dwarf galaxies.
What is great is that future spacecraft like the James Webb Space Telescope (launching in 2018), and the WFIRST are equipped with O++ spectrum detectors. The aim is to spot very young galaxies forming their first stars and supernovae, and according to Malkan’s research, they’ll have plenty of targets to check. Malkan stated,”Detecting and studying the intense green glow from the youngest galaxies now looks like our best opportunity for learning how the first galaxies evolved.”
Photo source and reference: Engadget