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White dwarf stars can be purple, pink and even green, surprising new study finds

Research reveals the first known green star and the reddest star ever discovered among stellar cores

By LineZotpaper
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White dwarf stars come in a far wider range of colours than their name suggests, including pink, green, cyan, purple and yellow, according to a new study published in the journal RAS Techniques and Instruments. The research has identified what scientists say is the first known green star and the reddest star ever found.

White dwarf stars are the dense, cooling cores left behind when low- to medium-mass stars run out of fuel. The first known examples glowed white or pale blue, leading to the name 'white dwarf'. But new research shows these stellar remnants can emit a surprising variety of visible-light colours.

Mark Hollands, an astronomer at the University of Warwick in the U.K. and the study's first author, said the findings challenge expectations. "Most stars, including most white dwarfs, behave like 'perfect radiators', so their colour is set almost entirely by temperature. But nobody had really looked into what else might be possible for white dwarfs," he said in a statement. "It turns out these incredibly dense stars can produce colours nobody expected, and some of them genuinely surprised me."

The variety of colours is possible because of the unusual density of white dwarfs. Cooler white dwarfs have a density of about 1 gram per cubic centimeter, similar to water on Earth, but they are also millions of times denser than the Sun's visible surface. These extreme conditions create a palette far beyond the typical white or pale blue glow.

The study, published Thursday 15 October, identifies the first ever green star and the reddest white dwarf ever recorded, though the researchers have not released specific names or catalog numbers for the objects. The findings suggest that the term 'white dwarf' may be a significant understatement.

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Analysis

Why This Matters

  • The discovery expands the known colour spectrum of white dwarfs, challenging a long-standing assumption that their appearance is determined almost entirely by temperature.
  • Understanding the full range of white dwarf colours could provide new clues about their composition, age, and evolutionary history.
  • The identification of extreme colours like green and deep red opens up new avenues for identifying and classifying these common stellar remnants.

Background

White dwarfs are the final evolutionary stage of most stars, including the Sun. After a star exhausts its nuclear fuel, it sheds its outer layers, leaving behind a hot, dense core that slowly cools over billions of years. Until now, astronomers have generally classified them by temperature, with the hottest appearing blue-white and the coolest appearing yellow or red. The new study suggests that additional physical factors, likely related to their extreme density, can produce colours that do not follow the simple temperature-colour relationship.

Key Perspectives

Astronomers and study authors: The team at the University of Warwick argues that the colour diversity is real and stems from the unusual physical conditions inside white dwarfs, not just temperature variations. They plan to investigate the mechanisms behind the unexpected colours. Stellar astrophysics community: The research is likely to prompt re-examination of existing white dwarf catalogues to see if other unusual colours were overlooked, and to develop new models of how light interacts with the dense matter in these stars. Critics/Skeptics: Some astronomers may question whether atmospheric effects or instrument calibration could produce some of the observed colours. Confirmatory observations and theoretical modelling will be needed to rule out artefacts.

What to Watch

  • Whether follow-up spectroscopic observations confirm the green and red colours and identify the physical cause.
  • If other unusual colours are reported in existing white dwarf surveys, suggesting the phenomenon is more common.
  • Potential revision of white dwarf classification schemes to include colour as a parameter beyond temperature.

Sources

Zotpaper

Written by software from the reporting listed above, scored by an automated standards desk, and published without a person reading it first. If something here is wrong, tell the editor and it will be put right.

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