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Planetary News: Spitzer Space Telescope (2006)

Spitzer Space Telescope Captures Cosmic "Crime" as it Happens

By Amir Alexander
5 October, 2006

A team of scientists studying the most massive and energetic stars in the universe stumbled upon a cosmic "crime" in the making: the destruction of a potential planetary system. Led by Zoltan Balog of the University of Arizona's Steward Observatory, the astronomers were using the Spitzer Space Telescope to observe O-type stars, the largest and most powerful stars in the universe. With a mass of up to 100 times that of the Sun -- the radiation from O-type stars is one million times as powerful.

Too close for comfort
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Too close for comfort
The Sun-like star on the left wandered to close to the giant O-type star on the right, and is having its protoplanetary disk blown off. The comet-like tail shows that ongoing process of "photoevaporation" in this image from the Spitzer Space Telescope. Credit: NASA/JPL-Caltech/Z. Balog (Univ. of Ariz./Univ. of Szeged)

According to prevailing theories, the radiation from O-type stars is so strong, that it affects smaller stars that stray into the giant's neighborhood. In particular, O-type stars would burn away the disk of gas and dust that commonly surrounds young Sun-like stars. These clouds, known as protoplanetary disks, are the stuff from which planets are formed, and without them no planetary system can evolve. As a result, Balog and his colleagues expected to see nothing by bare stars in the neighborhood of the giant O-type, bereft of planets or of protoplanetary disks that form them.

What they actually saw was far more dramatic: A group of Sun-like stars in star-forming cloud IC 1396,  2450 light years away, had strayed close by a giant and violent O-star, and at least one of them was clearly in the process of losing its protoplanetary disk. "Unfortunately these Sun-like stars just got a little too close to the fire" observed University of Arizona Regents Professor George Rieke ruefully. It was like observing a crime as it happened.

The process captured by Spitzer is known as "photoevaporation." The enormous energy output from the O-star heats up the disks surrounding smaller neighboring stars to such a degree that the gas and dust literally boil off. When the disk can no longer hold together, photon (or light) blasts from the O-star blow the evaporated material into interstellar space. That was precisely the dramatic image that Balog and his group witnessed in the Spitzer images.

"To see protoplanetary disks in an area where no one expected to see one is very exciting" said Balog. "But to see a disk in the process of evaporation is even more thrilling."