FOR RELEASE: Tuesday, May 1, 9:30 AM ET
C. Robert O'Dell
((615) 343-1779,
cro@orion.phy.vanderbilt.edu )
Department of Physics & Astronomy, Vanderbilt University
Nashville, TN 37203
Contact number during the April Meeting:
Best Western, Manassas, VA, April 30 - May 1. 703-361-8000.
Popular Version of Paper
W2.001
Tuesday, May 1, 11:00 am
APS April 2001 Meeting, Washington, DC
The prevalence of stars accompanied by planetary systems may be substantially less than previously thought because the massive young stars in the rich clusters that serve as stellar nurseries produce such strong fluxes of radiation that they evaporate the protoplanetary disks of dust and gas surrounding other stars in the cluster long before planets can form.
This conclusion is based on recent observations and analysis of the Orion Nebula, the closest example of the type of stellar nursery that is generally considered to be the source of the vast majority of new stars in the galaxy. It hosts the youngest known cluster of stars and has been the target for several Hubble Space Telescope (HST) programs summarized in this paper.
In addition, there is a growing body of evidence that the youngest and brightest stars in the Orion Nebula are less than 100,000 years comparable in age with modern man-- and that the radiation from these bright stars will keep 90 percent of the newer stars currently forming in Orion from developing planetary systems.
Since we believe that most stars form in rich clusters Like Orion, we expect that the processes that operate there should be the common legacy of most stars.
In Orion we find numerous protoplanetary disks surrounding stars caught in the process of formation. A young star and its associated disk are called a proplyd. In many cases proplyds are accompanied by enormous jets--much larger than the solar system--flowing at hypersonic velocities that create spectacular celestial shock waves. Since these jets are found in only a small fraction of the proplyds, we conclude that they are created only during a brief, but spectacular period during a star's formation, when the conditions of material falling into the inner region of the disk and the magnetic field configuration are in the right combination.
The intense radiation from the young massive stars in Orion makes the proplyds highly visible. But it is also slowly destroying them. Recent measurements taken with the Keck and HST telescopes indicate that 90 percent of the disks will be destroyed in the next several hundred thousand years. The best current estimates for the time it takes a planet to form is several million years. So it appears that the disks will be destroyed long before planets can form. About 10 percent of Orion's proplyds are shielded from the destructive radiation and may ultimately evolve into planetary systems.
At the present there is no indication of depletion of even those disks closest to the brightest stars. This observation, together with a recent study of a key binary pair of stars in the cluster, suggests that the youngest and brightest stars in the cluster are no more than 100,000 years old and may be only a few tens of thousands of years old.
We know the environment within which this is happening because we have determined the detailed, three- dimensional structure of the Orion Nebula with data from HST, ground-based optical telescopes, and the Very Large Array radio telescope. This allows a hypothetical observer to look at the nebula and its associated proplyds, jets, and shock waves from any position in space.
With sponsorship of the American Museum of Natural History in New York, this information has been used to create a realistic, three-dimensional computer simulation of the nebula. An early version of the model was used to create the Orion portion of the 3-D flythrough "Our Milky Way Galaxy" that is shown in the Hayden Planetarium. It was also used recently to generate a flat-screen version of the flythrough that will be shown following the presentation.
RealPlayer video of Orion Flythrough