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 th Hubble Space Telescope images showing newborn stars and their pre-planetary disks in the Orion
Nebula have yielded a glorious animated flythrough of the region.
| Flying Through Orion |
| This animation takes the viewer on a conceptualized tour of the star-birthing region of the Orion Nebula. |
The data for this flythrough produced results similar to those
reported last week on SPACE.com. In the latest work, C. Robert O'Dell of Vanderbilt University and his colleagues now think the youngest and brightest stars in the star-birthing Orion Nebula are less than 100,000 years old (comparable in age with modern humans). The radiation from these bright stars will keep 90 percent of the newer stars currently forming in Orion from developing
planetary systems. The fact that these stars may not be any older than mankind itself doesnt sit well with O'Dell. It goes against the Copernican principle. Copernicus argued that Earth wasnt the center of the universe but, rather, that Earth orbits around the Sun. Since then this has been generalized to the Copernican principle: There is nothing special in time or space about Earths position in the universe.
"It is unlikely that Homo sapiens and the Orion Nebula should be formed at just about the same time, but perhaps we are just lucky," ODell said.
The anti-planet forming factor comes as a result of ultraviolet radiation from the newborn stars in the nebula. The radiation is so violent that
dust can hardly accumulate to form planets.The environment is now more familiar to astronomers who determined the detailed, three- dimensional structure of the Orion Nebula with data from
Hubble Space Telescope, ground-based optical telescopes and the Very Large Array radio telescope. The result is a 3-D simulated animation, which allows a hypothetical observer to look at the nebula and its associated protoplanetary disks, jets and shock waves from any position in space.
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.Jets versus proplyds
Since scientists believe that most stars form in rich clusters like Orion, they expect that the processes that operate there should be the common legacy of most stars.
O'Dell's work shows 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, said O'Dell, of Vanderbilt University.
Since these jets are found in only a small fraction of the proplyds, O'Dell thinks 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 Hubble 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 the disks likely will be destroyed long before planets can form. Still, about 10 percent of Orion's proplyds are shielded from the destructive radiation and may ultimately evolve into planetary systems.
Orion contains about 300 circumstellar disks, a large number for all that radiation, possibly because the central stars in the Trapezium cluster are relatively young, O'Dell said, and have yet to experience significant wear and tear to their surrounding disks from radiation.
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