Astronomers at UK university discover first ever green star in history

A new study into the stars has concluded that if we could view them up close, certain white dwarfs would shine in colours such as pink, cyan, yellow and purple, as well as green.

Although no white dwarf star is close enough for its colour to be seen directly, the team calculated it instead from data astronomers already collect routinely.

The team used a star's spectrum, its "fingerprint", which is produced when starlight is split apart by wavelength.

Dr Mark Hollands, Warwick Prize Fellow in the Astronomy and Astrophysics Group, University of Warwick, who led the work, said most white dwarf stars "behave like the perfect radiators".

He said: "Most stars, including white dwarf stars, their colour is set almost entirely by temperature. But nobody had really looked into what else might be possible for white dwarfs.

"It turns out these incredibly dense stars can produce colours nobody expected and some of them genuinely surprised me."

Mr Hollands explained that the WD J1330+6435 star has obtained its green glow due to its "enriched atmosphere", something never seen before.

The star is around 4,000C and has enriched its atmosphere with calcium, lithium, and sodium, giving it a chartreuse green appearance.

As far as the Warwick astronomers are aware, no other star, living or dead, has ever been credibly reported as green, making it the first known star of this colour in the Galaxy.

Mr Hollands said of the discovery: "The traces of sodium in the atmosphere of this white dwarf absorb the orange part of the spectrum, leaving behind a ghostly green glow.

"Imagine standing on a planet and looking up at a green star. It feels like something out of science fiction."

Applying their research to other white dwarf stars across the sky, the University of Warwick team found that white dwarf stars can appear in a variety of different colours, linked to their surrounding atmospheres.

Carbon-rich stars are typically pink or purple, while those enriched with debris from shattered asteroids and comets or remains of old planetary systems are more yellow.

Cooler white dwarfs with mixed hydrogen and helium atmospheres often take on a cyan or pale blue tinge, caused by hydrogen molecules colliding with helium atoms in their ultra-dense atmospheres.

Tracking their data against a representative sample of 151 white dwarfs within around 65 light years of Earth, five showed unusual colouring, two yellow and three pink.

They concluded that roughly one in 30 white dwarfs in the Universe will shine with an unusually coloured light.

Professor Boris Gänsicke, Department of Physics, University of Warwick, said: "One in 30 might not sound like a huge fraction, but across the entire population of white dwarfs in the Universe, that is still a lot of oddly coloured stars out there.

"Yet if we take the median across a representative population of white dwarfs, we found that the average white dwarf really is white."