BY THE OPTIMIST DAILY EDITORIAL TEAM
For most of human history, the night sky came in a limited palette. Orange for the cooler stars, white for something like our sun, pale blue for the hottest ones. The color of a star tracks with its temperature, roughly the way iron in a blacksmith’s forge moves from red to white-hot as it heats. It felt, more or less, like a closed model.
Astronomers at the University of Warwick just opened this model back up. The team discovered the first green star ever documented: a white dwarf called WD J1330+6435 that glows an unexpected chartreuse, the result of sodium absorbed from the ruins of a planetary system it once hosted.
“The traces of sodium in the atmosphere of this white dwarf absorb the orange part of the spectrum, leaving behind a ghostly green glow,” said Dr. Mark Hollands, who led the study. “Imagine standing on a planet and looking up at a green star. It feels like something out of science fiction.”
The chemistry of a dying star
White dwarfs form when stars exhaust their nuclear fuel and collapse under their own gravity, becoming extraordinarily dense cores of compressed matter. That density changes the rules. Elements absorbed into the star’s atmosphere interact with surrounding helium plasma in ways that filter starlight, absorbing specific wavelengths and letting others pass. The result is color tied to chemistry rather than temperature.
The team analyzed spectrum data from 151 white dwarf stars within 20 parsecs, or about 65 light-years, of Earth, then ran those spectra through a model of human vision to see how each star would look. Carbon-rich atmospheres glow pink or purple. Stars that have taken in material from asteroids, comets, or planets go yellow. And one star, having consumed the chemical remnants of an entire planetary system, glows green.
“Most stars, including most white dwarfs, behave like ‘perfect radiators,’ so their color is set almost entirely by temperature,” Hollands said. “But nobody had really looked into what else might be possible for white dwarfs. It turns out these incredibly dense stars can produce colors nobody expected, and some of them genuinely surprised me.”
The study, published in RAS Techniques and Instruments, suggests that a star’s color is not simply a temperature reading. It’s a chemical record of everything the star has ever absorbed, including the debris of planets that no longer exist.
White is still the most common color. Only about one in 30 white dwarfs will display an unusual hue, and none of these can be seen from Earth since no white dwarf is close enough for its true color to be visible without scientific instruments. Hollands says there’s something unexpectedly personal about this kind of mapping. “It gives you a nice human connection to these very distant things that are so far away that sometimes even as a researcher you feel quite disconnected from these objects that you study,” he told CNN. “But then you can sort of add a human element into it and it feels a lot more tangible.”
Source: RAS Techniques and Instruments – Any colour you like: the diverse chromaticities of white dwarfs
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