First green star discovered

Astronomers from the University of Warwick have identified the first green star, named WD J1330+6435, which is a white dwarf. This discovery challenges previous assumptions about the colors of dead stars.

Color depends on temperature

The color of a star is mainly determined by its temperature. Cold stars appear orange, while very hot stars are pale blue. White dwarfs, the remnants of stars like the Sun, were thought to follow the same color rules.

Unusual green color observed

Mark Hollands and his team converted the light from white dwarfs into colors visible to the human eye and found one appeared chartreuse green. This led them to investigate the source of this unusual color.

Cause of the green color

The green color of WD J1330+6435 comes from sodium and calcium in its atmosphere, which absorb parts of the light spectrum. These elements were brought to the star by rocky debris from its former planetary system.

Astronomical significance of the debris

The presence of heavy elements like sodium on the star’s surface is significant because these elements sink quickly into the star’s interior. The debris must have fallen recently for the elements to still be visible.

Human perception of the star's color

Using models of human color perception, researchers converted the star's spectrum into colors seen on a computer screen. However, no one has directly seen the star with the naked eye because it is too faint and distant.

Other unusual white dwarfs

The team studied 152 white dwarfs within 65 light-years of Earth and found only five with unusual colors. Most white dwarfs appear nearly white, with a median color temperature of about 6,800 kelvins.

Future discoveries expected

Mark Hollands and his colleagues believe there may be other white dwarfs with green or cyan colors. Future surveys could detect these stars, expanding our understanding of the diversity of white dwarf colors.