Astronomers at the University of Warwick have identified a white dwarf star that could appear green to the human eye, challenging conventional ideas about stellar colours. Their research also reveals that some of these stellar remnants glow pink, purple, yellow and cyan.
Published in RAS Techniques and Instruments, the study shows how the extreme density of white dwarf atmospheres can alter the colours of light they emit. White dwarfs are the compact remnants of stars that have exhausted their nuclear fuel.
Unlike ordinary stars, their atmospheres can contain trace elements such as carbon, calcium and sodium. Under high-density conditions, these elements interact with surrounding helium, absorbing light at particular wavelengths and changing the star’s apparent colour.
Led by Dr Mark Hollands of the University of Warwick, the team used stellar spectra — measurements of light across different wavelengths — and models of human colour vision to determine how the stars would appear to the naked eye.
One striking example, WD J1330+6435, has a temperature of about 4,000 degrees Celsius. Its atmosphere contains calcium, lithium and sodium from rocky material accreted from its planetary system. Sodium absorbs orange light, leaving a greenish appearance in the researchers’ models.
Another white dwarf, WD J1011+2845, about 48 light-years away, appears deep salmon-pink because carbon molecules distort its emitted light.
The researchers also examined 151 white dwarfs within 65 light-years of Earth. Five displayed unusual colours, suggesting that such stars are uncommon but not exceptionally rare. The sample’s median colour temperature was about 6,800 Kelvin, indicating that the typical white dwarf appears white rather than blue.