The white dwarf WD J1330+6435 would appear chartreuse green to human eyes because its dense atmosphere strongly absorbs parts of its light, including orange wavelengths absorbed by sodium. That is the result reported by University of Warwick researchers in a paper published on October 15, 2026 in RAS Techniques and Instruments. The colour was calculated from a spectrum and a model of human vision, rather than photographed from close enough for the eye to see the star’s colour directly.

The study matters because white dwarfs—the compact remnants left by stars such as the Sun—need not share the familiar range of orange, white and blue associated with ordinary stars. Their unusually dense, cool atmospheres can alter which colours escape. The green-star report is therefore an opportunity to explain how composition and pressure can change a star’s apparent colour, as well as temperature.

A dense white-dwarf atmosphere absorbs violet light through calcium and orange light through sodium; the altered spectrum enters a human-vision model and yields a green colour prediction.
Schematic of the study’s explanation: broad absorption changes the optical spectrum, which is then weighted by human-eye responses. The green patch is illustrative, not a photograph or a numerical reproduction of the measured spectrum.

The atmosphere removes colours from the light

The paper identifies broad sodium absorption that removes orange light from WD J1330+6435’s spectrum, while calcium absorbs in the violet. With those parts reduced, the remaining light peaks around 500 nanometres and produces the modelled green appearance. The authors connect the wide absorption features to the dense atmospheric environment. This is selective removal and reshaping of light, not a claim that the whole star emits only a single green wavelength.

The university links the atmospheric metals to accreted rocky material. For this object, the paper uses a physical effective temperature of about 4,240 kelvin, consistent with the press release’s rounded figure of about 4,000 degrees Celsius. Its unusual colour consequently cannot be read as a simple thermometer using the usual colour sequence for ordinary stars: atmospheric absorption is changing the light reaching an observer.

A spectrum is translated into human-eye colour

To turn the spectrum into a colour, the researchers weighted visible wavelengths by standard human-eye responses and calculated colour coordinates. They used the CIE 1931 colour system and converted the result into a colour representation for display. The university stresses that no white dwarf is close enough for us to see its true colour directly. The model asks how the light would look under suitable viewing conditions; it is not evidence that a casual telescope view will show this faint object as the same bright green.

That distinction also separates the work from the false-colour images often used in astronomy to show information outside human vision. Here the aim is to model a human-visible colour from an optical spectrum. Nevertheless, the displayed patch remains a representation of the calculation. An explanatory illustration, including the one above, is neither a new observation of the object nor a substitute for the measured spectrum and the paper’s method.

The new finding is the colour, with limits on its exact shade

WD J1330+6435 was already analysed in earlier work in 2021, according to the paper. What is new here is the colour result within the researchers’ wider investigation, rather than the first discovery that this object exists. The authors also say its spectrum is somewhat noisy, so its exact colour coordinates may shift. A different earlier model gives a similar broad hue, supporting the green appearance without fixing one perfectly certain shade.

The evidence supports a specific answer: a dense, metal-bearing atmosphere reshapes this white dwarf’s spectrum enough for a human-vision model to return green. The result broadens the colours that such stellar remnants can have, but it does not establish that all white dwarfs are green or provide a direct close-up colour photograph. The useful discovery is the connection between atmospheric physics and predicted appearance, with the exact shade still limited by the spectrum and modelling.

Sources & context

The University of Warwick release and the original RAS Techniques and Instruments paper were read directly. The explanation follows the optical-spectrum and human-vision method, including noisy-spectrum limits and the object’s earlier analysis. This is a modelled appearance, not a new close-up photograph. The original schematic is explanatory rather than measured evidence.

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