May 29, 2013
White Dwarfs Cool Slower Than Predicted
Lee Rannals for redOrbit.com — Your Universe Online
University of British Columbia (UBC) astronomers have determined that white dwarfs cool more slowly in the early stages of their life than models have previously predicted.
White dwarfs are the dense, hot remnant cores of stars that have used up all of their fuel and lost their outer layers during the red giant phase. When these objects form, their surface temperatures are very hot, but cool over time as they radiate their limited supply of heat into space. Scientists know that the cooler a white dwarf is, the older it is, but what has been harder to predict is the cooling rate seen in younger white dwarfs.
The UBC team studied white dwarfs in a globular cluster and found that white dwarfs actually cool slower in the early stages of their life.
“There are a number of important factors that contribute to the cooling rate of white dwarfs at high temperatures,” said UBC astronomer Ryan Goldsbury. “These include high-energy particle production, core composition, the composition of the stellar atmosphere, and the processes by which energy diffuses from the core outward. To pinpoint exactly where the difference between our theories and observations comes about, we really need more data.”
The team is currently observing the same star cluster with the Hubble Space Telescope to help them gather more data about white dwarfs. They are focusing their observations on the hottest and youngest white dwarfs in the dense central region of the star cluster. Eventually, the team hopes to obtain data on over 5,000 white dwarfs, which will be used to help explain the anomalous early cooling rate.
Scientists believe that white dwarfs may actually be able to host habitable planets. A team wrote in the Monthly Notices of the Royal Astronomical Society about a new theoretical study that even these dying stars could have exoplanets orbiting them in the habitable zone. They said that the 500 closest white dwarfs could contain one or more habitable exoplanets. Astronomers will have to wait until NASA's new James Webb Space Telescope (JWST) launches in order to advance the search for these white dwarf Earth-like planets.
“JWST offers the best hope of finding an inhabited planet in the near future,” said Dan Maoz of Tel Aviv University.
JWST will be able to detect oxygen and water in the atmosphere of Earth-like planets orbiting a white dwarf star. The space telescope is set to launch in 2018.