Astronomers identify the first green star, a chartreuse white dwarf 280 light-years away

Astronomers for the first time have identified a green star, documenting a dense stellar remnant called a white dwarf that became a ghostly shade of chartreuse after ingesting rocky debris from planets that once had orbited it, Reuters reported.

The star, named WD J1330+6435, is a white dwarf in the Milky Way about 280 light-years from Earth in the constellation Draco. Unlike normal stars, whose colour is governed by temperature, this white dwarf’s hue comes from chemistry: sodium-rich planetary material fell onto its surface, and in the star’s extreme density, helium atoms constantly bombard the sodium atoms, altering their energy levels.

The result, explained by lead author Mark Hollands of the University of Warwick in the journal RAS Techniques and Instruments: the sodium absorbs yellow, orange and some red wavelengths, leaving “a beautiful chartreuse green glow, something that wouldn’t be possible for sun-like stars”.

“Because white dwarfs are super-dense stars — they are roughly the size of the Earth, but contain about 165,000 times its mass — even a small amount of sodium blocks out a large amount of the orange light coming out of the star,” said co-author Boris Gänsicke.

The discovery was part of a project assessing how the colours of 151 white dwarfs within about 65 light-years would appear to human eyes. It also turned up perhaps the reddest known star hue: a salmon-pink white dwarf, WD J1011+2845, 48 light-years away in Leo Minor, coloured by carbon from its deep interior.

“It does show that the universe is sometimes just as weird as anything science fiction can conjure up,” Hollands said.