Astronomers at the University of Warwick have discovered that white dwarf stars can display a surprising variety of colors, including green, pink, purple, yellow, and cyan. Among their findings is the first known star that would appear genuinely green to the human eye. For most stars, color is closely tied to temperature.
Cooler stars appear orange, stars like our Sun look white, and the hottest stars shine pale blue. The relationship is similar to heating a piece of iron, which changes from red to orange and eventually white as its temperature rises. White dwarfs, the extremely dense remains of stars similar to our Sun, were long believed to follow this same pattern.
In fact, they received their name because the first examples discovered were unusually hot and appeared white or pale blue. However, scientists have now found that these stellar remnants can produce a much broader spectrum of colors. The findings, published in RAS Techniques and Instruments (RASTI), suggest that some white dwarfs would look dramatically different from ordinary stars if they could be viewed from close enough.
"Most stars, including most white dwarfs, behave like 'perfect radiators,' so their color is set almost entirely by temperature. But nobody had really looked into what else might be possible for white dwarfs," said Dr. Mark Hollands, Warwick Prize Fellow in the Astronomy and Astrophysics Group, University of Warwick, who led the work.
"It turns out these incredibly dense stars can produce colors nobody expected, and some of them genuinely surprised me." Why Some Dead Stars Glow in Unexpected Colors The explanation lies in the extraordinary density of white dwarf atmospheres. In the coolest of these stars, atmospheric material can reach densities of approximately 1 gram per cubic centimeter, comparable to water and millions of times denser than the Sun's visible surface, known as the photosphere. Under these extreme conditions, small amounts of elements such as carbon, calcium, and sodium interact with the surrounding helium plasma.
These interactions allow the elements to absorb a much wider range of light wavelengths than they would in less dense environments. As a result, the light escaping from a white dwarf can take on colors that would not normally be expected based on temperature alone. Instead of appearing orange, white, or blue, some of these stars develop entirely different hues.
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