National Science Foundation
Teachers Discover Unexpected Disks Around Interacting Stars
Highlight ID 12066RI_html_5f3a914.jpg

Artists concept of the dust cloud surrounding the interacting binary star system.

Credit: P. Marenfeld and NOAO/AURA/NSF
Permission Granted

New Spitzer Space Telescope observations of an unusual class of interacting binary stars detected excess amounts of infrared radiation, suggesting that these odd objects are surrounded by large disks of cool dust. The results were produced by one of six teams of professional astronomers and high school teachers participating in a unique program co-sponsored by the National Optical Astronomy Observatory (NOAO) and NASA's Spitzer Science Center.

The type of variable star system being studied by the team consists of a highly magnetic white dwarf star (a "dead" remnant star formed from the core of a star like our Sun when it exhausts the available fuel to support nuclear fusion) and a very low mass, cool object similar to a brown dwarf star. The two objects orbit so closely--about the distance from earth to the moon--that they make a complete revolution about each other in only 80-90 minutes. The white dwarf is earth-sized but weighs about 60 percent of the mass of the sun, while the companion star is Jupiter-sized but has about 40-50 times the mass of Jupiter.

The high mass of the white dwarf and the closeness of the companion result in mass exchange between the two stars. The gravitational influence of the white dwarf squeezes the companion star into a teardrop shape, and matter squirts from its pointed end toward the white dwarf, like water from the nozzle of a garden hose. This material eventually falls onto the white dwarf, causing tremendous heating of its atmosphere and the emission of a large amount of energy from x-rays to the far infrared.

To their surprise, the team found excess infrared emission around all four systems that they studied. The team's current best model for its origin is that a large, cool dust disk with a temperature of about 800-1,200 Kelvin (980-1,700 degrees Fahrenheit) surrounds the orbiting stars.

"Our explanation at this point is that the emission originates from a large, relatively cool disk of dust encircling the entire binary system," team leader Steve Howell of NOAO says. "The discovery of dust disks around these old interacting binaries is very exciting. We have shown our initial results to a variety of specialists, and nobody yet has a better idea of what we are seeing."

The research team also included Carolyn Brinkworth of the Spitzer Science Center, and physics teachers Howard Chun from Cranston High School in East Cranston, R.I.; Beth Thomas of Great Falls Public Schools in Great Falls, MT; and, Linda Stefaniak of Allentown High School, Allentown, N.J. Chun, Thomas and Stefaniak are graduates of NOAO's Teacher Leaders in Research Based Science Education, a teacher professional development program funded by the National Science Foundation.

  Web Policies and Important Links | Privacy | FOIA | Help | Contact NSF | Contact Web Master | SiteMap