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.
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.