The first known green star is WD J1330+6435, a dead star tinted by sodium

A star that would look green to human eyes has finally turned up, and it is a dead one. Astronomers at the University of Warwick worked out the true colour of dozens of burnt-out stellar cores and found one whose light, seen from close range, would glow a pale chartreuse green. No other star of any kind, living or dead, has ever been credibly shown to be green.

The same analysis turns up stellar remnants that would look salmon pink, purple, yellow or cyan, colours ordinary stars never take on. Anyone taught that stars come in red, orange, white and blue just gained a wider palette, even if no one will ever see it with the naked eye.

The star is called WD J1330+6435, a white dwarf in the northern sky. White dwarfs are what remains when a star like the Sun runs out of nuclear fuel, and they owe their name to the first examples found, which were hot and shone white or pale blue. This one sits at about 4,240 kelvin, and its atmosphere carries traces of sodium, calcium and lithium that it pulled in from the rocky wreckage of its old planetary system.

Recommended ReadingHubble data from 1999 points to a planet born after its star died

“The traces of sodium in the atmosphere of this white dwarf absorb the orange part of the spectrum, leaving behind a ghostly green glow,” said Mark Hollands, a Warwick Prize Fellow at the University of Warwick who led the work. “Imagine standing on a planet and looking up at a green star. It feels like something out of science fiction.”

How a computer saw colours no telescope shows

No telescope image can settle a star’s colour. White dwarfs are far too faint for the naked eye, the eye loses most of its colour sense in the dark even at the eyepiece, and survey pictures map their filters onto red, green and blue channels in false colour.

So the team skipped pictures and worked from spectra, the measurements that split a star’s light into its individual wavelengths. They used observed spectra from the Sloan Digital Sky Survey and the Montreal White Dwarf Database, plus model atmospheres from a code by Detlev Koester of the University of Kiel, and ran each one through the 1931 colour-matching functions of the International Commission on Illumination, the standard mathematical description of how human eyes respond to light, and converted into the sRGB colour space that ordinary screens use.

The result is the colour a person would perceive from close enough to see the star as a disc. The team also rendered those discs, including limb darkening, the way light dims and shifts toward a star’s edge. For WD J1330+6435, the centre comes out a vivid pale green and the outermost rim picks up a faint orange tint.

Why a dead star can turn green

A normal star behaves almost like a perfect glowing object, so its colour follows its temperature, the same way a heated iron bar goes from red to orange to white. “Most stars, including most white dwarfs, behave like ‘perfect radiators,’ so their color is set almost entirely by temperature. But nobody had really looked into what else might be possible for white dwarfs,” Hollands said.

What makes white dwarfs different is pressure. In the coolest ones, the atmosphere reaches about one gram per cubic centimetre, roughly the density of water and millions of times denser than the visible surface of the Sun. Crushed together at those densities, atoms of sodium, calcium or carbon absorb light across far wider bands of wavelengths than they would anywhere else.

In WD J1330+6435, a broad sodium feature swallows the orange part of the spectrum while calcium absorbs the violet end. What survives peaks at around 500 nanometres, in the green. Its colour comes from the debris it accreted, not from its temperature.

Pink, purple and cyan stars

The rest of the palette comes from different chemistry. White dwarfs with carbon dredged up from their cores form molecules that absorb right where the eye is most sensitive, and they come out pink or purple. One of them, WD J1011+2845, about 48 light-years away, sends almost all of its light at wavelengths longer than 600 nanometres and may be the reddest star ever documented, with a deep salmon-pink tone.

Cool white dwarfs that mix hydrogen and helium go the other way. Under extreme pressure, hydrogen molecules colliding with helium atoms absorb infrared light so strongly that the remaining light shifts toward blue, giving them a cyan cast despite their low temperatures. Another sodium-rich star, WD J2356-2054, is so blue that no temperature on the standard colour scale matches it, and the team calls it a more metal-rich version of the green star. Two more, WD J0851+1543 and WD J1351+2645, lean green far more faintly.

The average white dwarf is white after all

To check whether these oddities are common, the team looked at every known white dwarf within 20 parsecs, about 65 light-years, of the Sun, a census of roughly 150 stars. Five had unusual colours, two yellow and three pink, which points to about one white dwarf in 30 being something other than white across the galaxy.

The typical one is plain white. The median colour temperature of the nearby sample came out near 6,800 kelvin, close to a cool-white household bulb at about 6,000 kelvin. That corrects a common picture of white dwarfs as blue: hot, blue ones are brighter and visible from farther away, so they crowd brightness-limited surveys.

“One in thirty might not sound like a huge fraction, but across the entire population of white dwarfs in the Universe, that is still a lot of oddly colored stars out there,” said Boris Gänsicke, a professor in the Department of Physics at Warwick. “Yet if we take the median across a representative population of white dwarfs, we found that the average white dwarf really is white.”

What the colours don’t settle

The green verdict rests on a noisy spectrum. The authors acknowledge that WD J1330+6435’s real colour could differ slightly from their calculation. Their confidence comes from a second, older model of the same star, built with a different treatment of sodium in an earlier study, which also came out green.

The colours are also computed, not observed. They depend on model atmospheres for stars whose physics remains hard to reproduce, especially the carbon-rich ones, and on a standard model of human vision that does not capture every eye. The carbon-rich and metal-rich samples were picked to show extremes, so only the 20-parsec census speaks to how common each colour is, and it holds just five oddly coloured stars. No one can check the result by looking, either.

Common questions about green stars

Are there green stars?

Until now, no star had been credibly shown to look green. WD J1330+6435, a white dwarf with sodium and calcium in its dense atmosphere, is the first known example, according to the Warwick analysis.

Why don’t normal stars look green?

A normal star emits light across a broad range of wavelengths, peaking at a point set by its temperature. When a star’s light peaks in the green, it still emits plenty of red and blue, and the mix looks white to the eye. Only heavy absorption that cuts out other colours can leave a green tint.

Can you see a green star with a telescope?

No. WD J1330+6435 and other white dwarfs are far too faint for the naked eye, and through a telescope the eye loses its ability to distinguish colours in low light. The green colour is a calculation of what a nearby observer would see.

What colour are most white dwarfs?

White. Across all white dwarfs within about 65 light-years of the Sun, the median colour temperature is near 6,800 kelvin, which looks white to human eyes. About one in 30 shows an unusual colour such as pink or yellow.

What comes next

The paper, by Hollands, Gänsicke, Pier-Emmanuel Tremblay of Warwick and Koester, appeared online in RAS Techniques and Instruments on 15 October 2026, open access, after a preprint on 13 October. Warwick announced it on 19 October, Nature ran it as a research highlight two days later, and NASA’s Astronomy Picture of the Day showed an artist’s view of the green star on 22 October. The team offers its spectral models to other researchers on request and pitches the rendered discs for outreach.

The authors expect a larger sample of cool, metal-rich white dwarfs to fill in a continuous run of colours between the green WD J1330+6435 and the blue WD J2356-2054.

Reference: Hollands et al., “Any colour you like: the diverse chromaticities of white dwarfs,” RAS Techniques and Instruments, 2026. DOI: 10.1093/rasti/rzag069

Tags: astronomy, University of Warwick, green star, Mark Hollands, star colours, WD J1330+6435

More Like This

Webb watched water clouds thicken and thin on a world 7.4 light-years away

JWST found an object 100 billion times brighter than a star — not a star

James Webb found a planet where rock clouds form each morning and clear by night

A planet nursery was caught spinning for the first time, and parts ignore the rules

A planet orbiting backwards around a red dwarf has no giant neighbor to blame

JWST found ancient galaxies hiding four times their measured mass in small stars