White Dwarfs Aren’t Just White. Scientists Discover Dying Stars Turning Pink and Green

At the end of their lives, stars similar in mass to our sun expand into red giants and subsequently shed their gaseous envelopes, creating planetary nebulae. A white dwarf, a highly condensed object about the size of Earth but with a sun-like mass, remains. Initially, white dwarfs appeared white to light blue due to their high temperatures.

However, a new study in the journal RAS Techniques and Instruments reveals that white dwarfs can also display colors such as pink, green, and purple. Researchers attribute this diversity to density, with cooler white dwarfs reaching densities similar to water, about a million times denser than the sun's atmosphere. This density allows trace elements like carbon, calcium, and sodium to interact with the dense helium plasma, absorbing light across a broader spectrum.

Additionally, remnants from ancient planetary systems and collisions of asteroids and other bodies contribute to the atmospheric composition of white dwarfs. Carbon-rich white dwarfs appear pink or purple, while those with enriched material from shattered asteroids can exhibit yellow and green shades. The coolest white dwarfs often display a baby blue hue due to hydrogen and helium collisions in their dense atmospheres.

Examples include WD J1330+6435, which has accumulated rocky material from its planetary system, giving it a chartreuse color, and WD J1011+2845, enriched with carbon, appearing salmon-pink. WD J902-2010 leans more toward bubblegum colors. Despite these varied colors, most white dwarfs remain white. The study examined 152 white dwarfs within 65 light-years of Earth, finding that only five showed unusual coloration, suggesting that about one in thirty white dwarfs in the universe shines with unusual light.

This finding may seem expected, but previous studies had assumed white dwarfs were predominantly blue, likely due to observational bias favoring brighter, hotter stars. While the nearest white dwarf, Sirius B, is invisible to the naked eye, it accompanies the brightest star in Earth's night sky, Sirius, and can be observed during winter above the eastern horizon.