Astronomers evaluating the chemical light profiles of stellar remnants have identified what they report is the first known star to radiate with a green hue, according to a study published this week in the journal RAS Techniques and Instruments.
White dwarfs represent the compact embers left behind when stars similar in mass to the sun exhaust their nuclear fuel and collapse under gravitational pull. For typical stars, color corresponds directly with surface heat: cooler objects look orange or red, while hotter ones glow white or pale blue like heated metal. Because white dwarfs were long assumed to act as standard heat radiators, their observed colors were expected to follow that same temperature progression.
Atmospheres as dense as water
The research team, led by Mark Hollands of the University of Warwick in England, determined that extreme density alters how these stellar corpses look to human eyes. The outer atmospheres of the coolest white dwarfs can reach densities similar to liquid water, millions of times thicker than the surface of the sun, Popular Science reported.
At those extreme pressures, trace elements collide vigorously with surrounding helium plasma, changing atomic energy levels and absorbing light across broader sections of the color spectrum than occurs in lower-density stars.
“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 said in statements cited by the outlets.
Planetary debris produces a green glow
Because stars are too distant for observers on Earth to perceive their exact tints directly, the astronomers used recorded spectral data and human vision models to simulate what their light would look like close up. The models revealed that white dwarf WD J1330+6435 shines with a chartreuse green hue.
The green tint developed after the dying star pulled in and consumed rocky material from its planetary system, loading its atmosphere with calcium, lithium and sodium, Courthouse News reported. News organizations cited different distance measurements for the star: Space.com reported WD J1330+6435 is located approximately 326 light-years away, while Popular Science placed it around 284 light-years from Earth. Both outlets noted its temperature sits near 4,000 degrees Celsius, or roughly 7,200 degrees Fahrenheit.
“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 told Space.com. “Imagine standing on a planet and looking up at a green star. It feels like something out of science fiction.”
A diverse palette in deep space
The team also identified what could be the reddest star recorded: WD J1011+2845, situated 48 light-years from Earth. Convection inside that white dwarf dredges carbon from its core to the surface, distorting outgoing radiation so that light shifts past 600 nanometers and produces a deep salmon-pink appearance.
Other atmospheric compositions generate distinct appearances, researchers found: carbon-rich white dwarfs can gleam pink or purple, while stars dusted with fragments of pulverized comets and asteroids turn yellow. Collisions between hydrogen and helium produce cyan or pale blue hues in other cold remnants.
Despite these striking variations, unusual colors remain rare. An examination of 151 white dwarfs within 65 light-years of Earth uncovered only five with unconventional shades, indicating that roughly one in 30 white dwarfs across the universe displays an anomalous color. University of Warwick astronomer Boris Gänsicke noted that the median color temperature across representative dead stars remains white at roughly 6,800 Kelvin.
Scientists anticipate that continued analysis of these atmospheric colors will help astronomers better visualize complex physics and clarify the chemical makeup of pulverized planetary systems orbiting dead stars.
