Astronomers say they’ve discovered first green star

HOUSTON – Astronomers analyzing white dwarf stars have for the first time found a star that would appear green to human eyes, according to a new study. While for most stars, colour is temperature-dependent and limited to a few hues, white dwarfs, which are the dense remnants of sun-like stars that have died, can glow in an incredible range of colors, said lead study author Mark Hollands, an astrophysicist at the University of Warwick, England, on Thursday. “The colors that normal stars can have are pretty much only orange, white or blue,” Hollands told CNN.  “What we found is, for most white dwarfs, that’s the same as well. But there are some special cases where the physics in the outer layers of these stars are sufficiently strange that it causes actually quite big deviations in terms of their spectrum,” he said. These deviations are due to the interaction between the helium in their atmosphere and traces of other elements, which vary between white dwarfs, depending on what material has interacted with the star over the course of its lifetime. For instance, iron, magnesium and sodium, elements commonly found in rocks, can be found on the surface — potential evidence of a nearby former planetary system, or from “something like an asteroid that ventures too close to the white dwarf,” Hollands explained.  “It gets shredded up into dust, and then those rocky bits of dust and debris fall onto the white dwarf,” he said. “And then that gets mixed into the outer layers, and then you can actually use that to measure what the rocky stuff was made off,” Hollands said. “So we can actually use the white dwarf as a sort of diagnostic tool to actually measure the chemistry of planetary material,” he added. “The white dwarf is taking apart the planets, and we’re able to see what was actually inside that planet — the proportion of the different elements — and that gives us clues in how these planets were formed,” said Adam Burgasser, a professor of astronomy and astrophysics at the University of California San Diego. “It is a crime scene, and we’re kind of piecing through the evidence that we have left available to us, and that’s allowing us to kind of piece the story of what the planet was and how it was made way, way, way back in in history.” For this study, Hollands looked at the 151 known white dwarf stars that are within 20 parsecs, or around 65 light years, of Earth.