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The study indicates that white dwarfs, which are the remnants of stars that have run out of energy after their evolutionary stages, may appear in multiple colors, including pink, cyan, yellow, violet, and green, depending on the composition of their atmospheres and the elements present within them.
The color of most stars is determined by their surface temperature; cooler stars tend to be orange or red, while hotter stars appear white or blue.
It was believed that white dwarfs followed the same principle, as they are objects that radiate light across a wide range of wavelengths. However, the new study suggests that the composition of their atmospheres may play a significant role in determining the color they appear.
Mark Hollands of the University of Warwick, the lead researcher, said that most stars, including the majority of white dwarfs, behave like "perfect radiators," whose emission spectrum is determined primarily by their temperature, explaining that the color possibilities resulting from the chemical composition of these stellar remnants have not been sufficiently researched.
White dwarfs are characterized by immense density, as a large mass is concentrated within a relatively small volume. These conditions allow the elements in their atmospheres to absorb light at specific wavelengths, which alters the resulting spectrum and the color that can be observed.
Given that there is no white dwarf close enough to see its color directly, the researchers relied on spectral data that reveals how its light is distributed across different wavelengths, then used models that simulate the way the human eye perceives colors to estimate its actual appearance.
The results showed that the potential color of these stars is linked to the composition of their atmospheres; carbon-rich white dwarfs may lean toward pink or violet, while some dwarfs whose atmospheres have been polluted by remnants of previous planetary systems may appear yellow, whereas some cooler dwarfs with hydrogen- and helium-rich atmospheres appear blue.
The white dwarf "WD J1330+6435" caught the researchers' attention, as data indicates that its temperature is about 4000 degrees Celsius, and that it has captured rocky material from its former planetary system, leading to the presence of elements such as calcium, lithium, and sodium in its atmosphere.
It is believed that these elements contributed to giving it a pale green glow, in a phenomenon that reflects the effect of chemical composition on the light emitted by the star.
Hollands explained that traces of sodium absorb part of the orange light in the spectrum, leaving the impression of a pale green glow.
The study opens the door to a broader understanding of the physical and chemical properties of white dwarfs, and their colors and spectra may help scientists explore the materials that have accumulated in their atmospheres, including remnants of planets and rocky bodies that orbited their stars before they turned into white dwarfs.
The research results were published in the journal "RAS Techniques and Instruments," providing evidence that the colors of these objects are not linked to temperature alone, but can also be influenced by the chemical elements present in their atmospheres.
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