UWM’s Kaplan helps identify the coolest known white dwarf

A team of astronomers has identified possibly the coldest, faintest white dwarf star ever detected. This ancient stellar remnant is so cool that its carbon has crystallized, forming – in effect – an Earth-sized diamond in space. “It’s a really remarkable object,” says David Kaplan, assistant professor of physics at the University of Wisconsin-Milwaukee (UWM). “We expect a large number of old white dwarfs to be around. They are just hard to see, and if we don’t know where to look, they are basically impossible to pick out.” White dwarfs are the extremely dense end-states of stars like our sun that have collapsed to form an object about the size of the Earth. Composed mostly of carbon and oxygen, they cool and fade over billions of years.

Kaplan and his colleagues found this 11 billion-year-old gem using the National Radio Astronomy Observatory’s (NRAO) Green Bank Telescope (GBT). But the telescopes didn’t actually allow scientists to see the white dwarf. Instead, they were studying a millisecond pulsar, found two years ago by Jason Boyles, now a visiting assistant professor at Western Kentucky University, using the GBT.