AILSA CHANG, HOST:
Now on to white dwarfs - stars, or more precisely the glowing remnants of certain stars. It turns out they're more colorful than their name suggests. Here's science reporter Ari Daniel.
ARI DANIEL, BYLINE: You can learn a lot about a distant star by examining the light streaming off of it, says astronomer Mark Hollands of the University of Warwick.
MARK HOLLANDS: You put it through something like a prism that splits the light up into its individual colors, and then you essentially measure how much light do you get at each color?
DANIEL: That unique rainbow helps paint a portrait of the star's atmosphere and its temperature and chemistry, which got Hollands wondering.
HOLLANDS: Oh, if I could see the star up close, what would it look like?
DANIEL: He was especially interested in white dwarfs, the leftover cores of dying stars that have shed their outer layers. They still glow, and they're so dense that a single teaspoon of star-stuff weighs as much as an elephant.
HOLLANDS: They are quite special objects unlike anything that we can study on Earth.
DANIEL: Hollands and his colleagues examined more than 200 white dwarfs within our Milky Way galaxy. Most of them turned out to be the same colors as other kinds of stars - white on average, pale orange if they're cooler and pale blue if they're hotter.
HOLLANDS: But we found that there are some exceptions.
DANIEL: These exceptions arise when a white dwarf's surface layers are made up mostly of helium, which is transparent. If material from a nearby planet or asteroid then enriches those layers, the white dwarf's telltale rainbow gets tweaked. In one case...
HOLLANDS: We're left with a spectrum that looks green.
DANIEL: Think chartreuse.
HOLLANDS: Typically, people would describe a star appearing green as something that's quite implausible. But with these extreme densities, we found that it is possible in very, very rare cases. It's fascinating to imagine.
DANIEL: For other white dwarfs, the carbon in their cores found its way to the surface.
HOLLANDS: And the end result is that these have a nice pink glow to them. And in one case, it's more like a salmon pink, so it's a really beautiful color.
DANIEL: There were a few white dwarfs that glowed yellow and still others that luminesce turquoise. The findings are published in the journal RAS Techniques and Instruments.
BARBARA CASTANHEIRA ENDL: It was actually very surprising and very cool. We wouldn't expect to see a star green or magenta or all these colors.
DANIEL: Barbara Castanheira Endl is an astrophysicist at Baylor University who didn't participate in the research. She says all these colors can tell us something about the composition and character of white dwarfs.
CASTANHEIRA ENDL: So this gives us another tool, a different way for us to see the stars.
DANIEL: For NPR News, I'm Ari Daniel.
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