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Study finds some nearby white dwarfs look pink, green or purple
A study in RAS Techniques and Instruments finds that density and absorbed planetary debris can tint some cool white dwarfs pink, green or purple, Wired reported.
- New headline Was: “White Dwarfs Aren’t Just White. Scientists Discover Dying Stars Turning Pink and Green”
- Our desk filed its story
Some nearby white dwarfs appear pink, green or purple rather than white or blue, according to a study in RAS Techniques and Instruments described by Wired1.
White dwarfs are the dense remnants left after sun-like stars shed their outer layers, roughly Earth-sized with about a solar mass1. The first examples found were hot and looked white to light blue, which is how the class got its name1.
The researchers argue density is the key, Wired reported. Atmospheres of the coolest white dwarfs can reach about 1 gram per cubic centimeter, comparable to water and about a million times denser than the sun's atmosphere, so carbon, calcium and sodium in dense helium plasma absorb light over a wider color range1.
Debris from planets and asteroids that migrate inward after the red-giant phase can also mix into the atmosphere1. Carbon-rich white dwarfs tend toward pink or purple; those enriched by shattered bodies can look yellow or, in some cases, green, according to the account1. The coolest often look baby blue because of hydrogen and helium collisions in dense gas1.
Wired cited WD J1330+6435, about 4,000 degrees Celsius with calcium, lithium and sodium, as a light chartreuse object described as the first known green star in the galaxy1. WD J1011+2845, rich in carbon, was described as salmon-pink, with most of its radiation beyond 600 nanometers; WD J902-2010 was described as leaning toward bubblegum pink1.
The authors examined 152 white dwarfs within 65 light-years of Earth; five showed unusual coloration, suggesting about one in 30, Wired reported1. Most remain white, so the name is not expected to change1. Earlier work may have over-counted blue objects because hotter white dwarfs are brighter and easier to see at greater distances1.
Sirius B, companion to Sirius, was described as a more typical light-blue white dwarf at about 25,000 Kelvin1. The Wired article is a translation of a story that first ran on WIRED Czech Republic and Slovakia1.
