Warwick astronomers identify first credible green star, white dwarf WD J1330+6435

Mixed · 2Astronomers at the University of Warwick have identified what they describe as the first credible green star: a white dwarf named WD J1330+6435. 1 2 Centre · 1CNA reports that the star lies about 280 light-years from Earth in the constellation Draco, and that the study was published in the journal RAS Techniques and Instruments. 2 Mixed · 2No white dwarf is close enough for its colour to be seen directly, so the team calculated the colours as human eyes would see them from spectra that astronomers already collect routinely, including Sloan Digital Sky Survey observations, and from white dwarf spectrum models they developed. 1 2

Mixed · 2Lead author Dr Mark Hollands said planetary material has fallen onto the star's surface, enriching its outer layers in calcium, lithium and especially sodium. 2 1 Mixed · 2Hollands explained that the star's density is so high that surrounding helium atoms constantly bombard the sodium atoms and alter their energy levels, so the sodium absorbs yellows, oranges and some reds rather than one narrow orange wavelength, leaving a chartreuse green glow. 2 1 Right · 1GB News gives the star's temperature as around 4,000C and says that, as far as the Warwick astronomers are aware, no other star, living or dead, has been credibly reported as green. 1

Mixed · 2Across the wider sample, the team found white dwarf colours fall into groups by atmospheric composition: carbon-rich stars are typically pink or purple, stars enriched with debris from shattered planetary systems lean yellow, and cooler stars with mixed hydrogen and helium atmospheres tend towards cyan or pale blue. 2 1 Mixed · 2The researchers studied 151 white dwarfs within about 65 light-years of Earth; GB News says five showed unusual colouring (two yellow, three pink) and that the team concluded roughly one in 30 white dwarfs shine with unusual colour, while Professor Boris Gänsicke said the average white dwarf really is white. 1 2 Centre · 1CNA adds that one of the sample, WD J1011+2845, 48 light-years away in Leo Minor, showed perhaps the reddest hue of any known star, a salmon pink, caused by carbon from the star's deep interior rather than by an external impact. 2