Astronomers Found Something They Thought Couldn’t Exist: A Green Star

Astronomers had never before convincingly identified a green star.

RelatedPosts

New capture technology scrubs atmospheric CO2 on the cheap
New study claims Mars had oxygen-rich atmosphere 4 billion years ago
NASA releases atmospheric simulation of this year’s hurricane season
Snowfall in the Alps is full of plastics particles

The universe is full of red stars, blue stars, and white stars. But green? Despite billions upon billions of stars scattered across the cosmos, astronomers had never convincingly identified a green star.

Now, they’ve found one. And the explanation is stranger than you might expect.

Why aren’t there any green stars?
Stars come in different colours because they have different surface temperatures. Relatively cool stars glow reddish-orange. Hotter stars appear white or bluish-white, with the hottest giving off a distinctly blue tint.

You might reasonably expect stars with intermediate temperatures to appear green.

In fact, some stars emit their greatest amount of visible light at green wavelengths. Our own Sun is a good example. Its spectrum peaks around the green part of the visible spectrum, depending on how the light is measured.

But nobody looking at the Sun from space would really describe it as green. It’s essentially white. The explanation lies in the difference between emitting green light and looking green.

Stars don’t emit just one colour. They produce a continuous spectrum of light containing many wavelengths, much like the colours of a rainbow. The proportions change with temperature, but the different colours are always mixed together.

When a star’s spectrum peaks in green, it still produces plenty of red and blue light. Our eyes combine those wavelengths and perceive the result as white. This is why you can find stars that look reddish, orange, white, or bluish, but not the vivid green of a traffic light or a laser pointer.

Astronomers describe this behaviour using something called blackbody radiation. It’s a mathematical model that predicts how an object radiates light based on its temperature

But it turns out that one unusual class of dead stars can break the pattern.

The dead star that turned green
WD J1330+6435 is a white dwarf, the dense stellar remnant left behind after a star exhausts its nuclear fuel and sheds its outer layers. Our own Sun will also eventually become one.

White dwarfs are extraordinary objects. They typically pack a mass comparable to the Sun’s into a sphere roughly the size of Earth. Their gravity is immense, and although they no longer sustain the nuclear fusion that powers ordinary stars, they remain extremely hot for billions of years as they slowly cool.

WD J1330+6435 has an estimated surface temperature of around 4,240 Kelvin, or about 3,970°C. That would ordinarily make it look reddish-orange.

But it also has an atmosphere; and that atmosphere is really unusual.

Astronomers had already studied the star because its spectrum contained unusual amounts of lithium, sodium, and calcium. These elements are clues that the white dwarf has accumulated rocky material from bodies that once orbited it. That material could have come from shattered asteroids or other remnants of its former planetary system.

The new research suggests that this chemical pollution is also responsible for its green appearance.

Pollution on a star

Basically, the star looks green because its atmosphere acts a bit like a filter.

White dwarfs can have extremely dense atmospheres. In some of the coolest ones, the gas is packed so tightly that atoms constantly bump into each other.

This changes the way the star’s atmosphere absorbs light. In WD J1330+6435, sodium absorbs a broad swath of yellow and orange light, while calcium absorbs some light at the violet end of the spectrum.

With those colours partly removed, more of the remaining light falls in the green range. As a result, the star would appear a pale yellowish-green, often described as chartreuse. Chartreuse is also a French herbal liqueur that has been made by Carthusian monks since the 18th century.

“The traces of sodium in the atmosphere of this white dwarf absorb the orange part of the spectrum, leaving behind a ghostly green glow,” explained lead author Mark Hollands of the University of Warwick in a university statement.

But has anyone actually seen a green star?
Well, not really.

No astronomer has directly photographed WD J1330+6435 as a resolved green disc. The object is extremely faint and far too distant for us to see its surface directly.

Researchers have only reconstructed what the star would look like if a human observer could approach it closely enough. But they’re still pretty confident it’s green. I mean, chartreuse.

They started with stellar spectra, measurements that reveal how much light an object emits at different wavelengths. A spectrum is essentially a detailed breakdown of starlight. By examining which wavelengths are missing or diminished, astronomers can identify chemical elements in a star’s atmosphere and investigate the conditions there.

The researchers used atmospheric models to reproduce these observations. They then passed the resulting spectra through mathematical models of human colour vision, calculating how the light would appear to our eyes.

They even generated realistic-looking images of the stars, accounting for the way brightness and colour change toward the edges of a stellar disc.

There are uncertainties. The star’s measured spectrum is somewhat noisy, so its exact shade could differ from the model. However, the team is confident that the star really would have a green appearance.

And WD J1330+6435 isn’t entirely alone. The researchers identified two other, much paler greenish white dwarfs. One of them, WD J0851+1543, has a higher-quality spectrum that supports its unusual colour.

Green isn’t the only surprise.

The researchers also identified white dwarfs that would appear pink, purple, yellow, or cyan, their unusual colours shaped by the chemistry of their atmospheres. Such stars are rare: just five of the 152 nearby white dwarfs studied had markedly unusual colours.

These exceptions reveal something remarkable. A star’s colour can tell us not just how hot it is, but also what it’s made of and, sometimes, what happened to its planets. In the case of WD J1330+6435, that strange greenish glow may carry the chemical traces of worlds destroyed long ago.

For decades, astronomers had good reasons to believe green stars couldn’t exist. It turns out the universe found a loophole.

The study, “Any colour you like: The diverse chromaticities of white dwarfs,” was published on 15 October 2026 in RAS Techniques and Instruments.