Astronomers have for the first time identified a green star, documenting a dense star remnant known as the white dwarf, which has received an unusual green shade after absorption of rock remains from planets that once turned around.
A star’s color is usually determined by its temperature. The coldest stars have orange images, the sun and stars similar to them look white, while the hottest stars are pale blue.
However, the situation is different with the white dwarfs. These are the remains of low – or medium – size stars that have drained their nuclear fuel and thrown out the layers.
Most white dwarfs have colors similar to other stars, usually white. But changes in their chemical composition may, over time, produce some of these rarer colors.
Newly identified star called WD J1330+6435, is a white dwarf in the Milky Way galaxy. It is located some 280 years away from Earth, in the starry of the Dragon.
We began to take an interest in this white dwarf because fragments of planetary material had fallen on its surface, enriching outer layers of elements such as calcium, lithium and, especially, sodium, said Astrophysicist Mark Hollands from the University of Warwick in England, the lead author of the study published in RAS Techniques and Instruments magazine.
In the common stars, sodium absorbs a very specific wave length of orange light, the same shade that gives characteristic color to street lamps used by sodium.
Yet, in this white dwarf, density is as high as sodium atoms are constantly bombarded by surrounding helium atoms, which alter their atomic energy levels, Holland explained.
As a result, sodium atoms no longer absorb a very narrow wave length of orange color. They absorb yellow, orange, and certain shades of red. What remains is a star with a beautiful green glow, something that would not be possible in stars similar to the sun, he added.
The discovery is part of a project intended to determine the colors of white dwarfs as the human eye would see.
A white dwarf usually has about half the mass of the sun, packed to a size similar to that of the earth.
Since white dwarfs are extremely dense stars, they have approximately the size of the Earth, but they contain about 165 times more mass. Therefore, even a small amount of sodium blocks much of the star’s orange light, said astrophysicist Boris Gänsicke, coauthor of the study by Warwick University.
Gänsicke compared this process to mixing colors in the gym of a painter, where removing a color from the mixture changes the final outcome.
A Pink salmon Star
Researchers also analysed 151 white dwarfs located within a radius of about 65 years of light from Earth. White was the most common color.
One of them had a pink salmon shade, which may be one of the deepest colors recorded in a star. It’s called WD J1011+2845, and it’s located about 48 years away from Earth in the Little Lion constellations.
In this case, color change did not cause sodium but carbon from the inside of the star.
The data used by researchers included observations of the spectrum of light from the Sloan Digital Sky Survey project, developed with a telescope in the American state of New Mexico, as well as patterns of the spectrum of white dwarfs developed by researchers themselves.
They found that the colors of these stars are divided into different groups, depending on the atmospheric composition. White carbon – rich dwarfs usually appear in pink or purple, and those enriched by the remains of destroyed planetary systems tend to be yellow.
Scholars generally found that these stars can appear in almost all colors of the spectrum.
Although green stars appeared earlier in the works of science fiction, including the latest comic film “Supergirl,” WD J1330+6435 is the first documented case of a green star in reality.
This discovery shows that the universe is sometimes as strange as anything that could create science fiction, Holland said.
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