Astronomers identify the first known green star, a white dwarf
Astronomers have identified what they say is the first known green star, Reuters and Space.com reported. It is a white dwarf about 280 light-years away that swallowed rocky debris from its old planets. Sodium in its dense atmosphere absorbs orange and yellow light, leaving a green glow.
Astronomers have for the first time identified a green star, a dense stellar remnant called a white dwarf that turned a ghostly shade of chartreuse after taking in rocky debris from planets that once orbited it, Reuters and Space.com reported.
The star, named WD J1330+6435, is about 280 light-years from Earth in the constellation Draco, Reuters reported. A white dwarf is the leftover core of a low- to medium-mass star that has burned through its fuel, Reuters reported. Most look white, but changes in their chemistry can give some of them rarer colors, Reuters reported.
"We first became interested in this white dwarf because bits of planetary material have fallen onto its surface, enriching its outer layers in elements including calcium, lithium and, in particular, sodium," said lead author Mark Hollands of the University of Warwick, Reuters reported. The study was published in the journal RAS Techniques and Instruments, Reuters reported.
In normal stars, sodium absorbs one narrow band of orange light, Reuters reported. In this star, the density is so high that sodium atoms are constantly hit by helium atoms, so they absorb yellows, oranges and some reds instead, Hollands said, according to Reuters. "What you're left with is a star that has a beautiful chartreuse green glow," he said, Reuters reported.
The finding came from a project assessing the colors of white dwarfs as human eyes would see them, Reuters reported. No white dwarf is close enough for astronomers on Earth to see its true color directly, Space.com reported. "It turns out these incredibly dense stars can produce colors nobody expected, and some of them genuinely surprised me," Hollands said in a statement sent to Space.com.
The team studied 151 white dwarfs within about 65 light-years of Earth, Reuters reported. One, WD J1011+2845 in the constellation Leo Minor, showed perhaps the reddest hue of any known star, a salmon pink caused by carbon, Reuters reported. Space.com reported that white dwarfs rich in carbon should look pink or purple, while some cooler ones would glow cyan.
Co-author Boris Gänsicke compared the effect to a painter's palette. "Take away some of the color going into the mix, and the output will change," he said, Reuters reported.
What we know: Researchers say WD J1330+6435 would appear green to the human eye because of sodium in its atmosphere.
What we don't: How many other green white dwarfs exist, since the color is worked out from light measurements, not seen directly.
Where outlets agree Reuters and Space.com report that astronomers led by Mark Hollands identified the first known green star, a white dwarf colored by sodium from planetary debris.
Where they differ The outlets cited here report the same key facts so far.