Using radio telescopes in California and New Mexico, NASA scientists have acquired the first images of material collapsing onto a newly born star, the same process by which the solar system began to form 4.6 billion years ago.
The star is embedded in a distant gas cloud called Bok Globule B335. The region of the sky observed is in the direction of the constellation Aquila, located about 800 light-years from Earth.
The scientists, working at NASA's Jet Propulsion Laboratory, captured a picture of the outer part of a seminal version of the solar system in its early stages of formation -- that is, a young star surrounded by a disk of matter in which planets could develop, forming from the collapse of a large cloud of gas.
This protostar, however, is only half as massive as the Sun. The size of the collapsed region imaged by the JPL scientists is about 7,000 times that of Earth's orbit around the Sun. That distance is comparable to the outermost regions of the solar system, where comets form.
The protostar, B335, has been studied for years, but its collapsing envelope has never before been imaged. Results of the radio telescope imaging by Drs. Thangasamy Velusamy, Thomas Kuiper and William Langer have been published in the Oct. 1 edition of Astrophysical Journal Letters.
The young star in B335 is only about 150,000 years old and the infall of matter has been going on for about as long, the scientists said. The infall is fueling the growth of material in the star and its disk and contributes to their chemical composition. Langer noted that it was important to study the composition of this infalling gas to understand the chemical makeup of the early solar system before planets began forming.
Langer said the scientists used the NASA Deep Space Network 70-meter antenna at Goldstone, Calif., and the Very Large Array at Socorro, N.M., to image the star-forming process at this early stage before all the gas had collapsed to the central star and disk.
The first direct imaging of the B335 infall required combining the data from these telescopes to resolve both the large-scale and small-scale structures of the central object at the same time, the scientists said in their paper.
The observations used the radio emission of a chemical CCS, called dicarbon monosulfide, to trace the motion of the infalling gas. CCS is one of more than 100 molecules that have been detected in interstellar space and that are used to trace the properties of star-forming gas.
Langer said such studies are important to understand how stars and planets form. The phenomena observed matches the theory of the formation of the solar system -- that is, a large gas cloud collapsed to form a star with an attendant circumstellar disk in which, over time, planets accreted from the matter in the disk and orbited the Sun.
The observations were made at Goldstone between May 1993 and June 1994. The Very Large Array maps were made on February 22 and 23 of this year and then again on March 2. The scientists praised the unique capabilities of these two radio telescopes for making this type of work possible, given the weakness of the radio signals.
The research was performed while Dr. Velusamy held a U.S. National Research Council senior resident research associateship and was on leave from the Ooty Observatory in India. The paper, published in the current issue of Astrophysical Journal Letters, is available via Internet by World Wide Web at the address http://DSNra.JPL.NASA.gov/~kuiper/.
The three scientists performed the work under contract to NASA's Office of Space Science, Washington, D.C. The Very large Array of the National Radio Astronomy Observatory is operated by Associated Universities Inc., under contract to the National Science Foundation.
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