Astronomers Say They Have Discovered the First-Ever Green Star

Illustration of first green star discovered by astronomers

Artist's depiction of the green star. (Image credit: Mark A. Garlick/University of Warwick)

Astronomers at the University of Warwick have discovered the first-ever green star. This exciting find is part of a larger study on the true colors of white dwarf stars. While this may inspire you to go stargazing in search of a green-hued twinkle in the night sky, the reality is a bit more complex than that. Still, this new research reveals that our universe may be a bit more colorful than previously thought.

The study, published in the journal RAS Techniques and Instruments (RASTI), explores what white dwarf stars would look like if we could see them up close. White dwarfs are the dense, leftover core of a dying sun, which results from stars no longer having the energy support themselves against their own gravity, causing their collapse.

Stars having different colors is nothing new. However, their hues are limited to a smaller spectrum that signals their temperatures. Cool stars shine orange; medium-temperature stars like our sun glow white; and the hottest of the bunch achieve a pale blue tone, a similar spectrum to a blacksmith’s iron, which goes from bright red to white-hot as its temperature rises. But now, the astronomers, led by Dr. Mark Hollands, have spotted how other elements that have come in contact with the dying stars can result in other colors.

“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,” Hollands says in a press release. “It turns out these incredibly dense stars can produce colors nobody expected, and some of them genuinely surprised me.”

Since no white dwarf is close enough to see its true colors from Earth, the scientists analyzed the spectrum data of 151 known white dwarf stars that are within 20 parsecs, or around 65 light-years, of our planet, splitting their starlight by wavelength. The team then ran this information through a model of human vision, obtaining what color each star would look like. “It is a reminder of just how much a spectrum can reveal: not just a star’s temperature or its chemical makeup, but its true color as well,” says the University of Warwick.

Due to white dwarfs being millions of times denser than active stars, elements like carbon, calcium, and sodium can interact with the surrounding helium plasma and absorb light across a wider range of colors. As such, stars with abundant carbon glow pink or purple, while those that feature remains from asteroids, comets, and planets acquire a yellow hue.

The most surprising finding was that the atmosphere of a star known as WD J1330+6435 absorbed calcium, lithium, and sodium from the remnants of a planetary system it once homed, giving it a chartreuse green glow. “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 explains. “Imagine standing on a planet and looking up at a green star. It feels like something out of science fiction.”

For all the colors they came across, the scientists share that white continues to be the most common hue of them all, as only one in 30 white dwarfs in the universe will boast an unusual color. Still, they appreciate the connection between their celestial subject of study and the way our eyes process lights and colors here on Earth.

“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,” Hollands tells CNN. “But then you can sort of add a human element into it and it feels a lot more tangible.”