Duncan Lorimer and Maura McLaughlin, professors in the Department of Physics and Astronomy, using the National Science Foundation’s Green Bank Telescope and other instruments have identified the coldest, faintest white dwarf star ever detected.
This ancient stellar remnant is so cool that its carbon has crystalized, formingin effect an Earth size diamond in space.
The story began when WVU graduate student Jason Boyles, now a visiting assistant professor at Western Kentucky University, discovered a rapidly rotating star called a pulsar with the GBT. He determined that the pulsar had a companion star, and the team undertook optical observations to search for it.
Any “normal” star like the sun, Lorimer said, should have easily been visible. But nothing was detected, implying that the companion is a white dwarf, a star roughly the size of the Earth, with a mass similar to the sun.
“The interesting thing about white dwarfs is that they’re actually solid objects. It’s not like the sun, which is a ball of gas. These stars are very, very dense, and because they don’t burn, they’ve got no new heat source. What they’re actually doing is cooling down,” he said.
“They were initially very hot, but over time they’ve cooled down. If you could measure how hot the star was, and you knew how fast it was cooling down, you could figure out how old the star was.”
White dwarfs are the extremely dense end-states of stars like the sun that have collapsed to form an object approximately the size of the Earth. Composed of mostly carbon and oxygen, white dwarfs slowly cool and fade over billions of years. The object in this new study is likely the same age as the Milky Way, approximately 11 billion years old.
Pulsars are rapidly spinning neutron stars, the superdense remains of massive stars that have exploded as supernovas. As neutron stars spin, lighthouse-like beams of radio waves, streaming from the poles of its powerful magnetic field, sweep through space. When one of these beams sweeps across the Earth, radio telescopes can capture the pulse of radio waves.
The pulsar companion to this white dwarf, dubbed PSR J2222-0137, was the first object in this system to be detected.
The team learned that the temperature of the dwarf star was less than 3,000 degrees Kelvin, which is very cold for a star of this nature. White Dwarf stars, Lorimer said, are usually between 10,000 and 15,000 degrees Kelvin.
“The white dwarf is so cool, it challenges the way we think about how these stars cool. It can’t be any older than the galaxy. It can’t be too cool; otherwise it would have been formed before the galaxy. What we think has happened is that it has entered the crystallized cooling regime in which white dwarfs cool very efficiently. This is one of the first times that this has been observed.”
The lead author of the project is David Kaplan, professor of physics at the University of Wisconsin – Milwaukee. A paper describing these results was recently accepted for publication in the Astrophysical Journal.
For more information, contact Duncan Lorimer at 304-293-4867 or firstname.lastname@example.org.