Recent events in the Orion Nebula observed by Hubble support the theory of a gaseous cloud. The Orion Nebula is located in the constellation Orion and appears as the fuzzy star in the hunter's sword. This beautiful region of the sky is noted for the abundant star formation that has made it the largest and most intense area of starbirth in our part of the Milky Way. The young stars produced are stellar infants -- only 300,000 years old.
The mere presence of star fomation would have been enough for the Orion Nebula to lure astronomers' curiosity, but it is not the stars that have attracted so much attention. It's what surrounds these stars: protoplanetary disks.
Photo. A spectacular view of part of the Orion Nebula -- about 1,500 light years distant. This region has experienced recent (relative to astronomical terms) star formation, about 300,000 years ago; the gas clouds were ejected by the recent creation of a star. The clouds are illuminated by the brightest of the stars, shining in the upper-left hand corner. Many of the other young stars are surrounded by disks of gas and dust, which makes the Orion Nebula important for understanding protoplanetary disks. Courtesy Space Telescope Science Institute, C.R. O'Dell/Rice University, NASA.
The proplyds of the Orion Nebula have provided astronomers a timepiece by which they can now view planetary evolution much like that of our solar system. The proplyds observed have strikingly similar chemical makeups to our planet, implying that if planets are someday accreted in the Orion Nebula, they will at least accumulate from ingredients similar to that from which Earth emerged.
In the meantime -- at least 50 million years -- astronomers will begin to understand the characteristics of these proplyds. They have already found the average newborn star with a circumstellar disk is generally one-fifth the mass of the Sun and the average disk contains 7 times the mass of the Sun.
Perhaps the most important discovery made by the imaging survey was that of the 110 stars examined, 56 had proplyds. Since over half of these stars had proplyds, astronomers believe that protoplanetary disks are common during star formation. The presence of proplyds provides the new star with the potential to control a solar system. If 50% of the stars in the universe were given this opportunity, the chances that some of these proplyds had accreted into planets would be overwhelming.
Other proplyds have been located around the stars Beta Pictoris, Formalhaut, and Vega. The old age of these stars, however, implies that the disks present will never form planets. The proplyds in the Orion Nebula are far more significant, since they surround stars much younger than any other stars observed which control protoplanetary disks.
Photo. Protoplanetary disk around Beta Pictoris. This is a smoothly rendered photograph that was taken edge-on looking at the disk. The bright bulge in the lower, left-hand corner is the center of the disk and one half of the disk is seen trailing off in what appear as streaks. Courtesy Space Telescope Science Institute, A. Schultz (CSC), NASA.
