Astronomers at the University of Warwick have identified what they believe is the first genuinely green star. Named WD J1330+6435, it is a white dwarf, the extremely dense remains of a star like the Sun. Its temperature is approximately 4,000 degrees Celsius. Other white dwarfs can appear pink, purple, yellow or pale blue.
No white dwarf is close enough for people to distinguish its colour directly with their eyes. Instead, the team analysed spectra, measurements that separate starlight into different wavelengths. They used a model of human colour vision to calculate how the stars would look. Although temperature usually determines a star's colour, the dense gas surrounding white dwarfs can change which light escapes. The green star has collected rocky material from its former planetary system, adding elements including sodium. Sodium absorbs orange light, leaving a green appearance.
To investigate how common unusual colours might be, the researchers examined 151 white dwarfs within about 65 light-years of Earth. Two appeared yellow and three pink. The findings suggest that roughly one in 30 white dwarfs could have an unexpected colour. However, the team's measurements showed that a typical white dwarf would still look white.
