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.
Spirals, ellipticals, rings and irregulars, they glow blue, white or red, depending on their stellar populations.
The most violent star-forming galaxies and nebulae are so hot they turn red, as ultraviolet radiation ionizes neutral hydrogen.
When the ionized electrons recombine with the nuclei, they transition between energy levels, emitting a particular set of wavelengths of light.
But there’s another, green line that happens only when oxygen gets doubly ionized at the hottest temperatures of all: 50,000 K and above.
Only planetary nebulae, with super-hot young white dwarfs, and the ultra-rare “green pea” galaxies exhibit these features.
But by looking at the most active star-forming galaxies in the Subaru Deep Field (above), Matthew Malkan and Daniel Cohen found, that all galaxies from 11 billion years ago or more emit this green signature.
The unexpected brightness and hotness of these galaxies hints that the stars in the ultra-distant Universe are somehow hotter than the hottest stars today.
These early galaxies are likely the type that reionized the Universe.
JWST, launching 2018, will find out for sure.
Mostly Mute Monday tells the story of a single astronomical phenomenon or object in mostly visuals, limited to no more than 200 words.