Warped Disk Around Nearby Star May Hide a Planet
(From the March/April 1998 issue of StarDate magazine)
A disk of dust around the star Beta Pictoris, a young, Sun-like star about 63 light-years from Earth, has chemical properties similar to objects in our solar system and may harbor a planet. The disk, seen edge-on from Earth, appears to be developing in the same way astronomers think our solar system developed 4.5 billion years ago.
Sergio Fajardo-Acosta of the University of Denver led a team that analyzed the composition of the dust particles at the outer edge of the disk orbiting Beta Pictoris. Their work builds on similar analysis of the inner disk done by other astronomers in 1996.
Like our solar system, this area of the Beta Pictoris system is the realm of cold, icy objects. Fajardo-Acosta says the dust particles, which range in size from microscopic to a few kilometers, have the chemical signatures of a silicate mineral called olivine and ice not unlike comets orbiting the Sun. Further study of Beta Pictoris will help astronomers better understand how comets formed in our solar system.
Images of the Beta Pictoris disk obtained by two teams using Hubble Space Telescope's planetary camera and imaging spectrograph show bulges or warps in the disk, which astronomers think could be caused by a planet.
Images of circumstellar disks are difficult to obtain. Few stars with disks are close enough to observe, and of those that are, few are oriented with their disks edge-on from Earth, the best angle for detecting planets. The star's glare must be overcome as well. Heap's team used one of Hubble's recently installed instruments to mask the glare of Beta Pictoris, while leaving more of the reflected glare of the dusty disk than had ever been observed.
A team of astronomers led by Fred Bruhweiler of Catholic University used Hubble Space Telescope to detect a warp in the outer region of the disk at a distance from Beta Pictoris equal to 750 times the distance between Earth and the Sun. Observations of the inner disk by Sally Heap of NASA's Goddard Space Flight Center and others revealed a similar bulge.
"It can't be explained except by some perturber that exerts a gravitational influence," says NASA Goddard Space Flight Center astronomer Sally Heap, who led one of the teams. A planet is the most reasonable explanation, Heap explained, since other explanations have been ruled out.
Bruhweiler says other scenarios could explain the outer bulge. The gravitational influence of a passing star or a brown-dwarf companion for Beta Pictoris could be responsible, he said.
"There's still a lot of debate about what's going on in the outer disk," Bruhweiler said. "The question is [are both bulges] caused by the same event or by two different things." -- Doug Addison
|
  |
Contact StarDate | About StarDate | Friends of McDonald | Sign up for Sky Tips
