New Delhi: Astronomers have identified a white dwarf star featuring an unusual yellowish-green glow, challenging conventional scientific understanding of stellar colors.
Named WD J1330+6435, the object is a white dwarf located about 280 light-years from Earth in the constellation Draco. It represents the first documented example of a star that appears greenish to the human eye, according to findings published in RAS Techniques and Instruments.
Unlike most stars, whose colors are largely determined by their temperatures, this stellar remnant owes its unusual appearance to the chemical elements present in its atmosphere. White dwarfs are the dense remains of stars that have exhausted their nuclear fuel and shed their outer layers, continuing to glow for billions of years.
WD J1330+6435 appears to have absorbed rocky debris left behind by planets that once orbited it, enriching its outer layers with calcium, lithium, and sodium. Lead author and astrophysicist Mark Hollands of the University of Warwick noted that researchers first became interested in the white dwarf because bits of planetary material had fallen onto its surface.
The key to the star's unusual color is sodium. In ordinary stars, sodium absorbs a narrow band of orange light, but the extreme density of a white dwarf alters how sodium atoms interact with surrounding helium atoms. This causes them to absorb a broader range of yellow, orange, and red light.
With more of these colors filtered out, the balance of light escaping from the star shifts, giving it a subtle yellowish-green hue known as chartreuse. The appearance is not a vivid, pure green, but rather the result of how the atmosphere alters the light reaching human eyes. Researchers analyzed the light spectrum and used models to calculate how the color would appear to human vision rather than photographing a green star directly.
Study co-author Boris Gansicke compared the process to a painter mixing colors, explaining that removing parts of the color mix changes the final output. The research team examined 151 nearby white dwarfs and found that their colors vary significantly depending on the chemical makeup of their atmospheres, with carbon-rich white dwarfs appearing pink, purple, cyan, pale blue, or yellow.
Researchers also identified WD J1011+2845, a white dwarf whose carbon-rich atmosphere gives it an unusual salmon-pink appearance, though its coloration stems from carbon rising from its interior rather than planetary debris falling onto the surface.
The findings demonstrate how studying white dwarfs can reveal the chemistry of stellar remnants while offering clues about the planetary systems that once surrounded them. Co-author Simon Hollands remarked that the discovery shows the universe can sometimes be just as strange as science fiction.