Mark Hollands and colleagues identified Green Star WD J1330+6435 as the first star to appear green to the human eye after it swallowed rocky material from its planetary system. The finding was published in RAS Technique and Instruments and adds a rare color to a class of dense stellar remnants that are usually described in white or pale blue.
The star sits about 284 light-years from Earth and has a surface temperature of roughly 7,232 degrees Fahrenheit, or 4,000 degrees Celsius. Hollands said, "Most stars, including most white dwarfs, behave like ‘perfect radiators,’ so their color is set almost entirely by temperature. But nobody had really looked into what else might be possible for white dwarfs."
WD J1330+6435 and its spectrum
WD J1330+6435 is a white dwarf, the dense remnant left after a star like the Sun runs through its nuclear fuel and sheds its outer layers. The work used spectra to infer how the star would look to the human eye, since there are no white dwarfs close enough to observe directly in that way. That approach let the researchers connect the star’s chemistry to its color instead of relying only on temperature.
Hollands said, "It turns out these incredibly dense stars can produce colors nobody expected, and some of them genuinely surprised me." The study links that result to trace elements such as carbon, calcium and sodium interacting with the star’s dense helium plasma.
Mark Hollands on white dwarf colors
The published findings place white dwarfs in distinct color groupings. Carbon-rich white dwarfs are typically pink or purple, stars that have fed off debris from shattered asteroids and comets or the remains of old planetary systems lean more toward yellow, and cooler white dwarfs with mixed hydrogen and helium atmospheres often take on a cyan or pale blue tinge.
The atmospheres around the coolest white dwarfs can reach the same density as water and are millions of times more dense than the Sun’s photosphere. In that environment, swallowed planetary material can shift how light is absorbed across the visible range, which is how a star that would usually be judged by temperature alone can present as green instead.
RAS Technique and Instruments findings
The result gives astronomers a new way to think about white dwarfs when they read spectra for color and chemistry. For readers tracking this class of objects, the practical takeaway is simple: a white dwarf’s appearance is not limited to the old white-and-blue picture, and WD J1330+6435 now stands as the clearest example of that wider range.
