White dwarfs can glow pink, purple or green

Some white dwarfs may appear pink, purple or green rather than white, according to a study by researchers at the University of Warwick in the UK, reported by ERR.

White dwarfs are dense stellar remnants left behind when stars similar to the Sun burn out. Because none of the stars studied is close enough to Earth for its true colour to be seen directly, the researchers analysed their light spectra and used a model of human colour perception to estimate how they would look to people.

The team identified WD J1330+6435 as the first known green star in the galaxy. It has absorbed rocky remnants from its own planetary system. They also found a deep-pink star 48 light-years away, which is likely the reddest star identified so far.

An analysis of 151 nearby white dwarfs found that most appear white, but about one in 30 has an unusual hue.

The colours are linked to the stars’ extreme density. The atmospheres of cool white dwarfs are millions of times denser than the Sun’s outer layers, with a density closer to that of water. In these conditions, elements such as carbon, calcium and sodium behave differently as they interact with the surrounding dense helium.

In the green star, sodium absorbs the orange part of the spectrum, leaving a greenish glow. Pink and purple hues result when carbon rises from the star’s interior to its surface and alters its light. The findings were published in the journal RAS Techniques and Instruments.