Discovery of the first green star in the universe

- For the first time, astronomers have observed a star that appears green to the human eye, according to a new study that analyzed white dwarf stars. Mark Hollands, the study's lead researcher and an astrophysicist at the University of Warwick in England, said Thursday that the colors of most stars depend on their temperature and are limited to a small number of colors, but white dwarfs, which are the dense remains of sun-like stars that have died, can glow in an amazing variety of colors.

“The colors of ordinary stars are largely limited to orange, white, and blue,” Hollands explained to Ufaq News, adding: “We found that this also applies to most white dwarfs, but there are exceptional cases in which the physics in the outer layers of these stars are so strange that they cause really large deviations in their spectrum.” These deviations result from the interaction of the helium present in the atmosphere of these stars with traces of other elements that differ from one white dwarf to another, depending on the materials that interacted with the star throughout its life.

Hollands explained that iron, magnesium and sodium, common elements in rocks, may be found on the surface of the white dwarf, which may indicate the presence of a previous planetary system in its vicinity, or to “an object such as an asteroid that came too close to the white dwarf.” He added: "The asteroid disintegrates into dust, and then those rocky parts and dust residues fall on the white dwarf."

He continued: "These materials mix with the outer layers of the star, which allows us to measure the components of the rocky materials from which they are composed." “We can use the white dwarf as a diagnostic tool to measure the chemical composition of planetary materials,” he said.

For his part, Adam Burgasser, a professor of astronomy and astrophysics at the University of California, San Diego, said: “The white dwarf disintegrates planets, and we can find out what was actually inside the planet, and the proportions of the various elements in it, which provides us with clues to how these planets were formed.” He added: "It is like a crime scene, and we are trying to collect the evidence remaining in front of us, so that we can reconstruct the story of the planet, what it is and how it was formed in the distant past."

Relevance to humans In this study, Hollands analyzed the 151 known white dwarf stars located just 20 parsecs from Earth, or about 65 light-years. As for Green Star, its main elements are calcium, sodium and lithium, according to Hollands.

Burgasser, who was not involved in the study, said: “This star sparked my interest and prompted me to study it more deeply, to understand why such a large amount of material has accumulated on it.” He added that this discovery may interest the public and scientists alike, and push them to learn more about the very special objects within this group.

Hollands pointed to another striking star, which appeared to have a “salmon-pink” color, due to its high density of carbon molecules. Although white dwarfs cannot be seen directly from Earth, Hollands was able to determine their colors using data from the spectra of stars, which form the "fingerprint" of light when analyzed by its wavelengths, just as a prism separates sunlight into the colors of a rainbow.

Hollands said that the research brings these distant objects closer to us, as it gives them a human dimension and makes them more real and tangible. For her part, Agnes Kim, an astrophysicist and professor of physics at Pennsylvania State University in Scranton, said that the study is based on existing data, but it presents an interesting way to look at white dwarfs, noting that the link between the spectra of stars and the colors seen by the human eye combines physics and biology.

Adam Burgasser, professor of astronomy and astrophysics at the University of California, San Diego, added that classifying white dwarfs according to their temperatures and the characteristics of their atmospheres helps to understand the reasons for their different colors and the relationship to their composition. Hollands intends to analyze the spectra of more white dwarfs, with expectations that the number of stars for which spectra data are available will increase tenfold, which could increase the number of observed green white dwarfs from one or two to 10 or 20.

The study was published in the journal RAS Techniques and Instruments (RASTI).