The First Green Star Ever Found Is a Dead Star That Ate a Planet

Look up at the night sky and you will see stars in only a few colours. Betelgeuse in Orion glows orange-red, Sirius sparkles bluish-white, and most of the rest look plain white. Ask any astronomy textbook why, and the answer is simple: a star's colour is set by its temperature. Cooler stars look orange, stars like our Sun look white, and the hottest look pale blue.

So here is a question that sounds almost silly. Can a star be green?

For the first time, the answer appears to be yes. Astronomers at the University of Warwick in the UK have identified a star that would look chartreuse green to the human eye if we could see it up close. And the reason for its strange colour is even stranger: it seems to come from the remains of rocky worlds that the star swallowed.

Who announced it?

The work was led by Dr Mark Hollands, a Warwick Prize Fellow in astronomy, together with Professor Boris Gänsicke, Pier-Emmanuel Tremblay (both of Warwick) and Detlev Koester of the University of Kiel in Germany. Their paper, titled Any colour you like: The diverse chromaticities of white dwarfs, is published in the journal RAS Techniques and Instruments. The University of Warwick announced the findings in a press release dated 15 October 2026, and National Geographic covered the "first green star" on 30 October 2026.

First, what is a white dwarf?

When a star like our Sun runs out of fuel, it puffs its outer layers into space. What remains is its core: a dead, extremely dense object roughly the size of Earth, called a white dwarf. It no longer burns fuel. It simply glows with leftover heat and slowly cools down over billions of years. Our own Sun is expected to end its life this way.

Why white dwarfs can break the rule

The secret is density. According to the Warwick team, the atmospheres of the coolest white dwarfs can reach about 1 gram per cubic centimetre, roughly the density of water and millions of times denser than the visible surface of the Sun.

In such a crushed, thick atmosphere, small traces of elements such as carbon, calcium or sodium behave very differently. Instead of absorbing light in narrow slivers, they soak up light across a much wider range of colours. Remove enough of one colour from a star's light, and what is left can look completely different to our eyes.

No white dwarf is close enough for us to actually see its colour. So the team worked it out from data astronomers already have: each star's spectrum, the rainbow "fingerprint" produced when starlight is split by wavelength. They ran these spectra through a standard model of human colour vision to calculate what colour each star would appear to a person.

Meet the green star: WD J1330+6435

The most striking result is a white dwarf with the catalogue name WD J1330+6435. The paper estimates its surface temperature at about 4,240 kelvin, which would normally make a star look orange.

But this star's atmosphere contains calcium, sodium and lithium. The researchers explain that the sodium, broadened by the dense atmosphere, absorbs the orange part of its light, while calcium absorbs at violet wavelengths. What survives peaks around the green part of the spectrum, giving a chartreuse green glow.

"The traces of sodium in the atmosphere of this white dwarf absorb the orange part of the spectrum, leaving behind a ghostly green glow," Dr Hollands said in the Warwick release. "Imagine standing on a planet and looking up at a green star. It feels like something out of science fiction."

The paper states that, to the authors' knowledge, no other star of any kind has been claimed to show a green hue. Two other white dwarfs in their sample also appear green, though much paler.

A star coloured by a swallowed world

Where did all that sodium and calcium come from? Not from the star itself. Astronomers understand that metals in such white dwarfs come from rocky debris, such as asteroids, falling onto the star from its old planetary system. In other words, the green colour is the visible aftermath of planetary destruction.

National Geographic quoted Dr Hollands as saying that around a quarter or more of white dwarfs contain traces of planetary debris in their atmospheres. Scientists find this useful: by reading the chemistry of what a white dwarf has swallowed, they can learn what the building blocks of planets around other stars were made of.

Pink, purple, cyan and the reddest star known

The green star is not the only surprise. The team found that white dwarfs fall into colour groups based on what is in their atmospheres:

• Carbon-rich white dwarfs, where carbon is dredged up from the core, are typically pink or purple.
• Those enriched with debris from shattered asteroids and comets tend towards yellow.
• Cooler white dwarfs with mixed hydrogen and helium atmospheres can look cyan or pale blue.

At the other extreme is WD J1011+2845, a nearby white dwarf about 48 light years from Earth. Carbon molecules in its atmosphere squeeze almost all of its light into wavelengths beyond 600 nanometres, giving it a deep salmon-pink glow. The paper calls it likely the reddest star known in terms of perceived colour.

So are white dwarfs actually white?

Mostly, yes. The team also studied all the known white dwarfs within about 65 light years of Earth, a fair, unbiased sample. Only five showed unusual colours: two yellow and three pink. That suggests roughly one in thirty white dwarfs shines in an unusual colour.

For the rest, the typical colour temperature came out at around 6,800 kelvin, which our eyes see as white. This corrects a common idea in astronomy that white dwarfs are usually blue.

"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 coloured stars out there," said Professor Gänsicke.

Why it matters

The study shows how much a strip of starlight can reveal, down to a star's true colour. Somewhere in our galaxy, a dead star is glowing green because it pulled in and consumed the rocky remains of its own planetary system. Surviving the death of your star, it turns out, is no guarantee of a peaceful retirement.