Green stars existed only in comics. Now astronomers have found the first real one and the reddest star ever recorded

Green stars have long been part of science fiction, appearing in comics and movies, including the recent movie Supergirl. But astronomers have now identified a real star with a rare green glow. Named WD J1330+6435, it is a white dwarf that acquired a ghostly chartreuse hue after ingesting rocky debris from planets that once orbited it, Reuters reported. The white dwarf lies in the Milky Way galaxy, about 280 light-years from Earth in the constellation Draco. A light-year is the distance light travels in a year, or about 5.9 trillion miles (9.5 trillion km).

How did the white dwarf turn green?

A star's color is generally determined by its temperature. Cooler stars tend to appear orange, the Sun and similar stars appear white, while the hottest stars glow pale blue.

White dwarfs, however, follow a different story. They are the leftover cores of low- to medium-mass stars that have exhausted their nuclear fuel and shed their outer layers. Although most white dwarfs appear white, changes in their atmospheric chemistry over time can give some of them unusual colors.


"We first became interested in this white dwarf because bits of planetary material have fallen onto its surface, enriching its outer layers in elements including calcium, lithium and, in particular, sodium," said astrophysicist Mark Hollands of the University of Warwick in England, the lead author of the study published in the journal RAS Techniques and Instruments.

In ordinary stars, sodium absorbs a specific wavelength of orange light. This is the same orange color that gives sodium street lamps their characteristic glow.

"In this particular white dwarf, however, the density is so high that the sodium atoms are constantly being bombarded by surrounding helium atoms, which alters the sodium atomic energy levels," Hollands said.

As a result, sodium absorbs a broader range of wavelengths instead of just a narrow band of orange light.

"The end result is that the sodium atoms no longer absorb one very narrow wavelength of orange — they absorb the yellows, oranges and some of the red wavelengths. 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.

The discovery emerged from a project examining the colors of white dwarfs as they would appear to the human eye. A typical white dwarf has about half the Sun's mass compressed into a volume roughly the size of Earth.

"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 Boris Gänsicke, a University of Warwick astrophysicist and co-author of the study.

Gänsicke compared the process to mixing colors on an artist's palette. Combining different colors produces a particular shade, while removing one color can change the final result. In the same way, the chemical composition of a white dwarf's atmosphere can alter the light it emits and the color astronomers observe.

Reddest star found too

The green white dwarf was not the only unusual discovery. Researchers studied 151 white dwarfs located within about 65 light-years of Earth, finding that their average color was white. One object stood out for its reddish hue. Named WD J1011+2845, it may be the reddest-colored star identified so far, with a salmon-pink appearance. It lies about 48 light-years from Earth in the constellation Leo Minor. In this case, carbon, rather than sodium, was responsible for changing the star's color. "Rather than something hitting the star, in this case the carbon comes out from its deep interior," Gänsicke said.

The researchers used light-spectrum observations from the Sloan Digital Sky Survey, conducted with a telescope in New Mexico, alongside white dwarf spectrum models they developed.

Their findings showed that white dwarfs fall into distinct color groups depending on the composition of their atmospheres. Carbon-rich white dwarfs generally appeared pink or purple, while those enriched by debris from shattered planetary systems tended toward yellow. Cooler white dwarfs with atmospheres containing a mixture of hydrogen and helium tended to appear cyan or pale blue.

Together, the observations revealed white dwarfs spanning almost every color of the spectrum.

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

With Reuter's inputs