One day, our sun will collapse into a superdense object about the size of Earth—a white dwarf. While our sun is an orangish-yellow, the resulting white dwarf will be… white obviously, right? Not necessarily. According to a new study from the University of Warwick, white dwarfs actually come in a rainbow of different colors.
The color of most stars is a function of its temperature: red stars are the coolest, orange and yellow stars are hotter, and blue and white stars are the hottest of all. “Most stars, including most white dwarfs, behave like ‘perfect radiators,’ so their color is set almost entirely by temperature,” study author and astrophysicist Mark Hollands explained in a statement. “But nobody had really looked into what else might be possible for white dwarfs.”
Read more: “Did Astronomers Finally Witness a Black Hole Eat a White Dwarf for the First Time?”
Why would they be different colors?
Well, the atmosphere of the coolest white dwarf stars is roughly as dense as water (still millions of times denser than our sun’s atmosphere). At this density, heavier elements like carbon, calcium, and sodium can mingle with the helium, absorbing their own unique wavelengths of light. That means that the true color of white dwarfs (the color our eyes would perceive if we could glimpse them up close) can vary.
Because these stars are too far away for us to see, Hollands and a team of astrophysicists analyzed existing data on the stars’ spectra, or the breakdown of the different wavelengths of light they emit. By running these wavelengths through a model of human color vision, the team was able to determine what color they would appear to our eyes.
“It turns out these incredibly dense stars can produce colors nobody expected, and some of them genuinely surprised me,” Hollands said.
For example, the atmosphere of white dwarf WD J1330+6435, which has some rocky material from its planetary system, includes trace elements of calcium, lithium, and sodium. According to the team’s model, it would appear chartreuse green to our eyes—the first known green star ever identified.
“The traces of sodium in the atmosphere of this white dwarf absorb the orange part of the spectrum, leaving behind a ghostly green glow,” Hollands said. “Imagine standing on a planet and looking up at a green star. It feels like something out of science fiction.”
The team also discovered the pinkest star ever, WD J1011+2845. This white (or pink?) dwarf 48 light-years from Earth has a deep convection zone that lifts carbon up to the atmosphere, distorting its starlight and giving it an otherworldly deep salmon color.
Of course, the average color of white dwarfs is still plain old white. After crunching the numbers on 151 white dwarfs within 65 light-years of Earth, the researchers found only five with extraordinary coloring (two were yellow, and three were pink). The rest would appear to us to be a cool white color, like an LED bulb. Great for lighting a cosmic kitchen at night, but nothing to write home about. 
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Lead Image: Mark Hollands/University of Warwick