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Peering into Orion nebula's stellar nursery.

Astronomers have viewed with greater clarity than ever before a dust-cloaked region of starbirth in the Milky Way, The violent interactions they recorded there may shed new light on luminous knots of gas, known as Herbig-Haro objects, whose origin has been controversial ever since they were discovered in the late 1940s.

Australian astronomers David A. Allen ol the Anglo-Australian Observatory in Epping and Michael G. Burton of the University of New South Wales used an infrared array to probe the interior of the dusty Orion nebula, a molecular cloud that harbors the stellar nursery nearest to Earth. They report their findings in the May 6 NATURE.

Their striking false-color images trace the high- and low-energy scenes from a startling story unfolding near the brightest star, dubbed IRc2, in Orion. Allen and Burton believe that the Herbig-Haro objects they recorded with the 3.9-meter Anglo-Australian Telescope were triggered by blobs of gas ejected from the star a mere 1,000 years earlier. Plowing into surrounding gas, the blobs ionized iron atoms, thus taking on a false-green cast. Surrounding many of these blobs are structures that resemble the bow shocks created when a boat rushes across a lake. Allen suggests that these bow shocks lack the punch to ionize iron but can excite molecular hydrogen, depicted as a red glow,

Other researchers say the images don't rule out alternative explanations for forming Herbig-Haro objects in Orion. C.R. O'Dell of Rice University in Houston notes that these knots might be formed when a slow-moving jet of gas from a star strikes a stationary wall of gas in the interstellar medium. Alternatively, a last-moving jet may create knots of bright emissions as it shocks and pushes out surrounding gas. Allen says that a narrow jet could not account for the wide angular spread of the knots. However, John Dyson of the University of Manchester in England suggests that a jet wiggling like the end of a loosely held garden hose might explain the distribution.

Researchers, including Allen, agree that more than one mechanism may create Herbig-Haro objects. In any case, writes Dyson in a commentary accompanying the NATURE article, the findings "show that many [violent] surprises are in store as modern observational techniques... probe into hitherto unexplored regions of interstellar space."
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Title Annotation:Herbig-Haro objects observed near IRc2 star
Author:Cowen, Ron
Publication:Science News
Article Type:Brief Article
Date:May 8, 1993
Words:378
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