Astronomers Identify First Green Star and Reddest Star Ever Recorded

Astronomers have identified the first star that would appear green to the human eye, as well as the reddest star ever recorded. The findings, published in the journal RAS Techniques and Instruments, focus on white dwarfs, the dense remnants of sun-like stars that have reached the end of their lifespans. While most stars appear orange, white, or blue based on temperature, researchers found that specific conditions in white dwarf atmospheres can produce unexpected colors.

The Physics of Stellar Color

For most stars, color is determined by temperature, behaving like "perfect radiators." However, the atmospheres of the coolest white dwarfs can reach densities similar to water, which is millions of times denser than the sun’s photosphere. In these dense helium plasmas, trace elements interact with light differently than they do in lower-density environments.

Mark Hollands, an astrophysicist at the University of Warwick and lead study author, explained the deviation from standard stellar behavior. "The colours that normal stars can have are pretty much only orange, white or blue," Hollands said. "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."

The study analyzed 151 known white dwarf stars within 20 parsecs, or around 65 light years, of Earth. Since no white dwarfs are close enough to be seen directly, the team calculated their apparent colors by running spectral data through a computer model of human vision.

Identifying the Green and Red Stars

The first green star identified is WD J1330+6435. Located approximately 284 light-years from Earth, this white dwarf has a surface temperature of about 7,232 degrees Fahrenheit (4,000 degrees Celsius). Its green appearance is caused by the accretion of rocky material from a former planetary system. The star's atmosphere is enriched with calcium, sodium, and lithium.

"The traces of sodium in the atmosphere of this white dwarf absorb the orange part of the spectrum, leaving behind a ghostly green glow," Hollands said. "Imagine standing on a planet and looking up at a green star. It feels like something out of science fiction."

The study also identified WD J1011+2845 as potentially the reddest star ever recorded. This white dwarf is 48 light-years from Earth and features a deep convection zone that lifts carbon from the star's core to its surface. The resulting carbon molecules absorb light across the optical range, squeezing the remaining light into wavelengths beyond 600 nanometres, which produces a deep salmon-pink glow.

Implications for Planetary Science

The presence of rocky elements on white dwarfs provides evidence of former planetary systems. When asteroids or planets venture too close to a white dwarf, they are shredded into dust and debris that falls onto the star's surface.

"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, who was not involved in the study. "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."

Frequency of Unusual Colors

Among the 151 white dwarfs studied, only five showed unusual colors: two yellow and three pink. This suggests that approximately one in 30 white dwarfs may shine with an unusually colored light. The median color temperature of the sample was approximately 6,800K, which appears white to the human eye.

Boris Gänsicke, a physics professor at the University of Warwick and co-author of the study, noted the significance of this ratio. "One in thirty might not sound like a huge fraction, but across the entire population of white dwarfs in the Universe, that is still a lot of oddly coloured stars out there," Gänsicke said. "Yet if we take the median across a representative population of white dwarfs, we found that the average white dwarf really is white."

Why it matters

This research corrects a common misconception that white dwarfs are typically blue. Because hotter, bluer white dwarfs are brighter, they are over-represented in surveys that rely on brightness. By analyzing a representative sample within 65 light-years, astronomers have established that the average white dwarf is white. Furthermore, the ability to use white dwarfs as "diagnostic tools" to measure the chemistry of planetary material offers new methods for understanding how planets form and evolve in other star systems.

---

Sources

• rnz.co.nz: Astronomers say they’ve discovered the first green star | RNZ
• popsci.com: Astronomers discover first green star and the reddest star ever recorded | Popular Science
• gizmodo.com: Astronomers Just Found the First Green Star Ever Discovered—Right After It Swallowed Its Planets

This article was drafted with AI assistance and checked against the sources above. Company claims are reported as claims. Cover image is AI-generated.