Circumstellar Disks

In the 1980's, astronomers using IRAS data discovered about two dozen stars which had infrared-emitting dust surrounding them, extending hundreds of astronomical units from the stars. (An astronomical unit is the average distance between the Earth and the Sun - about 93 million miles.) This discovery inspired astronomers to make more detailed observations of these stars. What they found around these young stars were flat, disk-shaped, areas of dust in which planets have formed or could be forming. These findings have led the way to one of the most exciting new areas of research in astronomy - the search for planets around other stars. The discovery of these circumstellar disks provided the first significant evidence that other solar systems might exist.

Credit Left Image: J.-L. Beuzit et al. (Grenoble Obs.), ESO
Credit Right Image: G. Schneider (Steward Observatory, U. Arizona), B.Smith (U. Hawaii), NIC MOS/IDT

The above left image is an infrared image of Beta Pictoris taken at the European Southern Observatory The presence of a warp in this disk indicates the existence of a Jupiter-sized planet around this star. There is also evidence for the existence of comets around Beta Pictoris. These disks of material are not usually seen by visible light telescopes. The visible light from a planet or disk of material is hidden by the brightness of the star that it orbits. In the infrared, where planets have their peak brightness, the brightness of the star is reduced, making it possible to detect a planet in the infrared. To aid in the detection of planets, infrared astronomers use occulting disks to mask out the light from a star allowing for a better view of possible planets. The above right image is an infrared view of a disk around the star HR 4796A taken with the Hubble's NICMOS camera. In this image you can clearly see where the light from the star (which is about 1000 times brighter than the disk) is blocked so we can better see the ring of material around the star. These disks contain the raw materials (dust and gas) from which future planetary systems can form.

A substantial amount of the Spitzer Space Telescope observing time will be devoted to the study of circumstellar disks, which are now thought to be a common feature of stellar evolution and of planetary system formation. Spitzer will study hundreds of nearby stars to help determine how often circumstellar disks occur. Spitzer will also study the composition and structure of these disks. This information will help us understand how planetary systems form.