Astronomers discover first documented green star 280 light-years away

Astronomers have identified the first documented green star, a white dwarf named WD J1330+6435, about 280 light-years from Earth in the constellation Draco. Its unusual chartreuse-green appearance developed after rocky debris from planets that once orbited it entered its atmosphere, according to a study published in RAS Techniques and Instruments.

The discovery matters because previously normal stars could be pretty much only orange, white or blue, Mark Hollands, an astrophysicist at the University of Warwick and lead author, told CNN. The finding shows that the universe is sometimes just as weird as anything science fiction can conjure up.

Hollands said the team first became interested in the white dwarf because bits of planetary material had fallen onto its surface, enriching its outer layers in calcium, lithium and especially sodium. In the white dwarf’s extremely dense atmosphere, sodium atoms are repeatedly struck by surrounding helium atoms. These interactions change their energy levels, allowing them to absorb yellow, orange and some red wavelengths instead of just a narrow band of orange. “And what you're left with is a star that has a beautiful chartreuse green glow, something that wouldn't be possible for sun-like stars,” Hollands said.

Researchers used spectral data and models of human colour perception to calculate how the star would appear, rather than relying on a direct photograph showing it as green, CNN reported.

The same study identified WD J1011+2845, a white dwarf about 48 light-years away with a rare salmon-pink colour that may be the reddest star recorded. For this star, the carbon comes from deep inside the white dwarf rather than from material hitting it.

To study the objects, researchers combined observations from the Sloan Digital Sky Survey, which used a telescope in New Mexico, with models of white dwarf spectra. Their analysis showed carbon-rich white dwarfs generally appear pink or purple, those polluted by planetary debris tend toward yellow, and cooler hydrogen-helium atmospheres can look cyan or pale blue.

Green stars have featured in science fiction, including the comic-book film Supergirl. This discovery provides a documented astronomical example of a colour long associated with imaginary worlds.

The white dwarf has an estimated temperature of around 4,000 degrees Celsius and is extremely compact, roughly comparable in size to Earth. A light-year is the distance light travels in one year, around 9.46 trillion kilometres, so astronomers observing the star today see it as it appeared 280 years ago.