Astronomers Discover First 'Zombie' Star with 'Ghostly Green Glow'
The star, WD J1330+6435, is believed to have acquired its unusual color by consuming debris from dead planets.
Astronomers have identified the first white dwarf star, nicknamed a "zombie" star, exhibiting a distinct "ghostly green glow." This unusual hue is attributed to the star's consumption of rocky material from defunct planets. The discovery was announced by a team from the University of Warwick.
The star, designated WD J1330+6435, is located in the Milky Way, approximately 280 light-years from Earth, and is faintly visible in the constellation Draco. This marks the first observation of a green star, revealing that the color of super-dense "zombie" stars can be altered by absorbed elements such as carbon, calcium, and sodium.
Typically, stars, including most white dwarfs, act as "perfect radiators," meaning their color is primarily determined by their temperature. Cooler stars appear orange, while hotter stars are pale blue. However, this new discovery demonstrates that white dwarfs can produce unexpected colors based on their atmospheric composition.
"The traces of sodium in the atmosphere of this white dwarf absorb the orange part of the spectrum, leaving behind a ghostly green glow," explained astrophysicist Mark Hollands. "Imagine standing on a planet and looking up at a green star."
White dwarfs are the remnants of stars that have exhausted their nuclear fuel and shed their outer layers. Without fusion to generate energy, they pull in and consume nearby celestial bodies, earning them the "zombie" moniker as they continue to exist after their primary life cycle.
The specific celestial bodies consumed by WD J1330+6435 included rocky material from a nearby planet rich in calcium, lithium, and sodium, which scientists believe is responsible for its green color.
Researchers noted that white dwarfs with high concentrations of carbon in their atmospheres would appear pink or purple. Those that have consumed asteroids, comets, or old planets would lean towards yellow. Cooling stars with a mixed hydrogen and helium atmosphere would exhibit a cyan or pale blue color.
In addition to the green star, astronomers also reported observing WD J1011+2845, a white dwarf approximately 48 light-years away that may be the reddest star ever seen. This star's salmon-pink glow is due to a deep convection zone that transports carbon from its core to its surface.
Scientists estimate that only about 3 percent of white dwarfs display such vibrant colors. "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 University of Warwick's Department of Physics. He added, "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 is expected to enter its white dwarf phase in approximately 5 billion years, after exhausting its hydrogen fuel and engulfing the inner planets of our solar system.