Astronomers identify WD J1330+6435, the first star that would look green to human eyes

White dwarf stars are the collapsed cores left behind when stars like the Sun run out of nuclear fuel and shed their outer layers. They are extraordinarily dense objects, typically packing about half the mass of the Sun into a volume roughly the size of Earth. Because they are so small and so hot, the first examples astronomers found glowed white or pale blue, which is how the class earned its name.

For most of the history of stellar astronomy, colour has been treated as a straightforward thermometer. Cooler stars look orange, stars like the Sun look white, and the hottest stars glow pale blue, much like a blacksmith's iron shifting from red to orange to white-hot as it heats up. White dwarfs were assumed to follow the same rule. Nobody had seriously checked what else might be possible for them.

A team at the University of Warwick has now done that checking, and the result is a genuinely new kind of object. The Warwick-led group reported on October 15, 2026 that a white dwarf catalogued as WD J1330+6435, roughly 280 light-years away in the constellation Draco, would appear chartreuse green to the human eye. According to the researchers, it is the first star of any kind ever credibly reported as green.

The study was published in the journal RAS Techniques and Instruments, known as RASTI. It was led by Dr Mark Hollands, a Warwick Prize Fellow in the Astronomy and Astrophysics Group at the University of Warwick in England, with co-authors including Boris Gansicke and Pier-Emmanuel Tremblay, and Detlev Koester of the University of Kiel.

Key Facts

Reuters reported on October 16, 2026 that astronomers had for the first time identified a green star, describing a dense stellar remnant that became a ghostly shade of chartreuse after ingesting rocky debris from planets that once orbited it. The object, WD J1330+6435, sits about 280 light-years from Earth in Draco. For scale, a light-year is the distance light travels in a year, about 5.9 trillion miles or 9.5 trillion kilometres.

The mechanism is not a trick of perception but a consequence of extreme density. In normal stars, sodium absorbs a very specific wavelength of orange, the same orange that gives sodium street lamps their characteristic colour. Hollands explained that in this particular white dwarf the density is so high that the sodium atoms are constantly being bombarded by surrounding helium atoms, which alters the sodium atomic energy levels. The end result, he said, is that the sodium atoms no longer absorb one very narrow wavelength of orange. Instead they absorb the yellows, oranges and some of the red wavelengths, and what remains is a star with a beautiful chartreuse green glow. Hollands added that this would not be possible for Sun-like stars.

The University of Warwick announced on October 15, 2026 that the star is roughly 4,000 degrees Celsius and has accreted rocky material from its planetary system, enriching its atmosphere with calcium, lithium and sodium. The team's models give the star its green appearance. Hollands said the work formed part of a project assessing the colour of white dwarfs as human eyes would actually see them, and that some of the results genuinely surprised him.

CNN reported on October 16, 2026 that the survey examined 151 known white dwarf stars within 20 parsecs, or around 65 light-years, of Earth. Hollands told CNN that the colours normal stars can have are pretty much only orange, white or blue, and that the same is largely true for most white dwarfs. There are special cases, however, where the physics in the outer layers of these stars is sufficiently strange to cause quite big deviations in the spectrum. Out of the 151 objects, only 5 showed extraordinary colours, and the team estimates that about 1 in 30 white dwarfs has an unusual hue.

Space.com reported on October 15, 2026 that the team also flagged what could be the reddest star ever recorded, the white dwarf WD J1011+2845, roughly 48 light-years away and coloured by carbon molecules. The same report noted that white dwarfs abundant in carbon should be pink or purple, while those enriched with debris from consumed asteroids and comets take on a more yellow hue. WD J1330+6435, a cool white dwarf that has been accreting rocky material from a planetary companion, is the most striking case of the set.

Analysis

What this really means is that stellar colour stops being a simple function of temperature once density becomes extreme. The textbook rule still holds for the vast majority of stars, including most white dwarfs, which the Warwick team describes as behaving like perfect radiators whose colour is set almost entirely by temperature. In a small subset, though, the physics of the outer layers is strange enough to push the spectrum far off the expected track. The green star is not an anomaly in the sense of an error. It is an anomaly in the sense of a regime that had simply never been catalogued.

The reason white dwarfs can do this comes down to what happens when trace elements meet an ultra-dense helium atmosphere. White dwarfs form when stars with roughly the mass of the Sun run out of fuel and collapse, and their matter ends up at around the density of water, millions of times denser than the Sun's photosphere. In those conditions, elements such as carbon, calcium and sodium interact with the surrounding dense helium plasma and absorb light across a much wider range of colours than they would in a normal stellar atmosphere. Space.com reported on October 15, 2026 that carbon-rich white dwarfs should appear pink or purple, and that the colour depends on which elements have been mixed into the outer layers over the star's lifetime.

The bigger picture here is that the debris falling onto these dead stars is doing double duty. CNN reported on October 16, 2026 that Hollands described the white dwarf as a diagnostic tool. Rocky material that ventures too close is shredded into dust, the debris falls onto the star and mixes into the outer layers, and the resulting chemistry can then be measured to work out what the original rock was made of. The green glow is a side effect of that pollution, but the pollution is the science. Elements commonly found in rocks, including iron, magnesium and sodium, turn up on the surface, which is potential evidence of a former planetary system or of an asteroid that strayed too near.

It is worth being precise about how unusual this is. Out of 151 nearby white dwarfs, only 5 showed extraordinary colours, and the team puts the overall rate of unusual hues at roughly 1 in 30. That makes WD J1330+6435 a rare specimen rather than a representative one, and it makes the broader colour catalogue the more valuable long-term product of the survey.

Why It Matters

Beyond the novelty of a green star, the result matters because it turns dead stars into forensic instruments. The elements accreted onto a white dwarf's surface preserve a record of what the bodies around it were made of. As Hollands told CNN, that lets researchers measure the chemistry of planetary material that no longer exists in any other accessible form. Studying the pollution on a stellar corpse is one of the few ways to probe the composition of worlds that were destroyed.

It also matters for how astronomers describe what they see. Colour in astronomy is normally shorthand for temperature, and that shorthand is taught, used and relied upon. If a subset of white dwarfs can appear green, pink, cyan, yellow or purple for reasons that have nothing to do with temperature, then colour alone becomes a less reliable first guess, at least for these objects. The Warwick work is not overturning stellar physics. It is mapping the exceptions, and the exceptions turn out to include a colour never credibly reported before.

The scale of the objects involved is part of the story too. A white dwarf is about the size of Earth but contains about 165,000 times Earth's mass. The same extreme density that makes these stars so strange is also what allows a trace of sodium, delivered by a shredded planet, to repaint the entire object as seen from the sky.

Next Up

The immediate next step is to broaden the colour census. The Warwick survey covered 151 white dwarfs within 20 parsecs, and the team already has a second candidate for the record books in WD J1011+2845. Larger samples should establish how often these strange atmospheres occur and whether the 1 in 30 estimate holds up. The full study appears in RAS Techniques and Instruments, with a digital object identifier of doi:10.1093/rasti/rzag069.

The green star itself is unlikely to change soon. At roughly 4,000 degrees Celsius it is a cool white dwarf, and its sodium-rich pollution is baked into its outer layers. For now, WD J1330+6435 stands as the first star of any kind that astronomers can credibly call green, a chartreuse point of light about 280 light-years away in the constellation Draco.