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Astronomers have discovered the first white dwarf “zombie” star with a “ghostly green glow” that they say it got from eating the rocky debris of dead planets.
“It feels like something out of science fiction,” said astrophysicist Mark Hollands, whose team from the University of Warwick announced its findings last week.
The zombie WD J1330+6435 is in the Milky Way, although about 280 light-years from our solar system, and can be faintly seen in the constellation Draco, the scientists said.
The discovery marked the first time researchers have seen a “green” star — and discovered that the color of such super-dense “zombie” stars can be changed by elements it absorbs such as carbon, calcium, and sodium.
“Most stars, including most white dwarfs, behave like ‘perfect radiators,’ so their color is set almost entirely by temperature,” Hollands told Space.com, explaining that cool stars look orange and hot stars appear pale blue. “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 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.”
White dwarfs in general are the leftover stellar core of a star that has stopped producing nuclear fuel and shed its outer layer during its red-giant phase.
Without fusion to sustain itself, it devours planets, asteroids and other heavenly bodies that get pulled into its supercharged gravity, leading it to be called a “zombie” star in the phase because it “lives” after “death.”
One of those celestial snacks — rocky material from a nearby planet containing calcium, lithium, and sodium — turned WD J1330+6435 green, scientists said.
Dwarf stars that have consumed high levels of carbon would be pink or purple, while those that consumed asteroids, comets or old planets would be more yellow. Cooling dying stars with a mixed hydrogen and helium atmosphere would appear cyan or pale blue, according to researchers.
In addition to spotting the green star, astronomers were also seeing red — announcing a white dwarf that could be the reddest star ever observed.
Stationed about 48 light-years away, WD J1011+2845 has a deep convection zone that brings carbon from its core to its surface — creating a salmon-pink glow, according to the study.
Scientists estimate that only about 3 percent of white dwarfs have vibrant coloring like the two they touted.
“One in thirty might not sound like a huge fraction, but across the entire population of white dwarfs in the universe, that is still a lot of oddly colored stars out there,” said Boris Gänsicke of the Department of Physics at Warwick to the outlet.
“Yet if we take the median across a representative population of white dwarfs, we found that the average white dwarf really is white.”
Earth’s sun will run out of hydrogen and engulf the inner planets of our solar system before entering its white dwarf phase in about 5 billion years.