Astronomers led by the University of Warwick have announced the discovery of the first star that would appear green to human eyes, challenging conventional understanding of stellar colours. This groundbreaking find involves a specific white dwarf star, which are the dense remnants of sun-like stars after they have reached the end of their lifespan.
The Ground-breaking Green Star Discovery
The newly identified green star, designated WD J1330+6435, is a white dwarf approximately 284 light-years from Earth and has a temperature of about 4,000 degrees Celsius (7,232 degrees Fahrenheit). According to lead study author Dr Mark Hollands, an astrophysicist at the University of Warwick, its unusual chartreuse green appearance is due to the presence of calcium, lithium, and sodium in its atmosphere. Specifically, the traces of sodium absorb the orange part of the spectrum, leaving behind a ghostly green glow. Dr Hollands remarked that the idea of looking up at a green star “feels like something out of science fiction.”
Unlike most stars whose colour is largely temperature-dependent – appearing orange, white, or blue – white dwarfs can exhibit a remarkable range of hues. This wider spectrum of colours is attributed to unique physical interactions within their outer layers, as reported by CNN. These deviations are caused by trace elements in the star’s atmosphere interacting with dense helium plasma, which can absorb light across a broader range of wavelengths.
Beyond Orange, White, and Blue: The Spectrum of White Dwarfs
The study, published in the journal RAS Techniques and Instruments, applied a method to calculate star colours from routinely collected spectrum data. This data, which acts as a “fingerprint” produced when starlight is split by wavelength (much like a prism splits sunlight into a rainbow), was run through a computer model simulating human colour vision. This revealed the true colours white dwarfs would exhibit if seen up close.
Researchers found that white dwarfs’ colours fall into distinct groups linked to their atmospheric composition. Carbon-rich white dwarfs often appear pink or purple. Those enriched with debris from shattered asteroids and comets, remnants of old planetary systems, tend towards yellow. Cooler white dwarfs with mixed hydrogen and helium atmospheres can show a cyan or pale blue tinge. Beyond the green star, the team also identified what could be the reddest star ever recorded, WD J1011+2845, a nearby white dwarf just 48 light-years away. Its deep salmon-pink glow is caused by carbon molecules lifted from its core, distorting its light into wavelengths beyond 600 nanometres, as detailed by Popular Science.
Dr Hollands, quoted by the University of Warwick, explained that the key to these varied colours lies in the extreme density of white dwarf atmospheres, which can reach roughly 1 gram per cubic centimetre – comparable to water and millions of times denser than the Sun’s photosphere. Under these conditions, trace elements like carbon, calcium, and sodium interact with the dense helium plasma to absorb light differently.
Implications for Planetary Science and Future Research
The discovery extends beyond just observing unusual star colours. White dwarfs can serve as a “diagnostic tool” to measure the chemistry of planetary material. Dr Hollands explained that when asteroids or planetary debris fall onto a white dwarf, their elements mix into the star’s outer layers. This allows astronomers to determine the composition of former planetary systems, providing clues about how those planets were formed. Adam Burgasser, a professor of astronomy and astrophysics at the University of California San Diego, likened it to a “crime scene,” where scientists piece together evidence of what a planet was made of.
The team studied 151 white dwarfs within 65 light-years (20 parsecs) of Earth, finding that approximately one in thirty white dwarfs in the Universe are likely to shine with an unusually coloured light. Professor Boris Gänsicke, from the University of Warwick, noted that this still represents “a lot of oddly coloured stars out there” across the entire population of white dwarfs.
The research also clarified a common misconception in astronomy: while hotter, bluer white dwarfs are often over-represented in surveys due to their brightness, the median colour temperature of a representative sample of white dwarfs is approximately 6,800 Kelvin, which human eyes perceive as white. Dr Hollands plans to continue analysing more white dwarf star spectra, with advancing scientific techniques enabling researchers to observe even more distant stars.
Frequently Asked Questions About Green Stars
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Can we see the green star directly from Earth?
No, white dwarf stars, including the newly discovered green star, are not close enough to be seen directly from Earth. Their colours are calculated using spectrum data and models of human vision.
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What causes white dwarfs to have unusual colours like green or pink?
The unusual colours are due to the extreme density of white dwarf atmospheres, which causes trace elements such as calcium, sodium, lithium, or carbon to interact with dense helium plasma and absorb light across a wider range of wavelengths than in typical stars.
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Where was this research conducted?
The research was led by Dr Mark Hollands, an astrophysicist at the University of Warwick in England, with findings published in the journal RAS Techniques and Instruments.
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What is the significance of studying these uniquely coloured white dwarfs?
Studying these stars allows astronomers to use them as a “diagnostic tool” to measure the chemical composition of rocky material from former planetary systems, offering clues about how distant planets were formed.
