Recent Warwick study found some white dwarfs appear non-white

Astronomers recently found that some white dwarf stars would not appear purely white. A University of Warwick-led research team reported the evidence in RAS Techniques and Instruments.

The featured image is an illustration of WD J1330+6435, a white dwarf star with an accretion disk. The disk holds gas and rocks in orbit around the star.

White dwarfs are small, faint stars left over when a Sun-like star exhausts its nuclear fuel. Some are too faint to see tonight, and trace elements accreted to them can interact with their atmospheres and shift their normally white color.

Stars appear as points in the sky and are mostly white, though sometimes noticeably red or blue. Blue stars are hotter than red stars. Star colors depend on surface temperature, and a true blackbody would only be red, orange, white or blue.

The University of Warwick led the research team and used computer models to study 151 white dwarfs within 20 parsecs from Earth. The objects were chosen for denser atmospheres, and the researchers investigated carbon, calcium and sodium effects.

The models showed 5 white dwarfs with pink or yellow appearances, including 2 yellow and 3 pink. Overall, 3.3 percent could exhibit non-white colors.

A carbon-atmosphere white dwarf can appear pink, and carbon can produce pink or purple. Cooler white dwarfs with hydrogen and helium can look cyan or blue, while white dwarfs with planetary debris can appear green.

The findings show that white dwarf color is not determined only by surface temperature. Trace elements and planetary debris can shift the expected white appearance, which matters for interpreting observations of these faint stars.