Astronomers from the University of Warwick have identified a white dwarf that, according to calculations, should appear ghostly green to the human eye. The object has been designated WD J1330+6435.
This is the dense remnant of a Sun-like star after the end of its life. Its surface temperature is about 4000 degrees Celsius.
The star has accumulated debris from rocky bodies of its planetary system in its atmosphere. The presence of sodium, calcium and lithium alters its emission spectrum.
Sodium absorbs the orange part of the spectrum, leaving a green glow. The researchers note that no other star — living or dead — has previously been reliably identified as green.
“Traces of sodium in the atmosphere of this white dwarf absorb the orange part of the spectrum, leaving a ghostly green glow,” says Dr Mark Hollands. “Imagine standing on a planet and looking up at a green star. It seems like something out of science fiction.”
A star's colour is usually determined by its temperature. White dwarfs, however, can deviate from this rule because of the high density of their atmosphere and impurities.
In a sample of 151 white dwarfs within 20 parsecs of Earth, five objects showed unusual hues. This suggests that roughly one in thirty white dwarfs in the Universe may have an atypical colour.
The average white dwarf, meanwhile, remains white. But how exactly do such rare cases affect our understanding of the evolution of stellar systems?
The results have been published in the journal RAS Techniques and Instruments. The modelling is based on spectra and takes into account the characteristics of human colour vision.
