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Studying one galaxy by looking at another.

A haze of dust prevents astronomers from clearly viewing the center of the Milky Way. But by observing Andromeda, the nearest similar galaxy, researchers have identified features that may mimic those at our own galaxy's core.

The X-ray picture at left, taken last year by the U.S.-British-German research satellite ROSAT and released last week, depicts Andromeda's X-ray core in unprecedented detail. It shows about 70 bright X-ray sources at the core, including 14 dense star regions known as globular clusters. Only 38 of these sources -- eight of them globular clusters -- appeared in observations by the orbiting Einstein Observatory in 1979 (image on right), note Francis A. Primini and Michael R. Garcia of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. This mismatch suggests that some X-ray sources might vary considerably over a 10-year period, they say.

The observations analyzed by Primini and Garcia were conducted during ROSAT's early, calibration phase and lasted for 30,000 seconds. Other ROSAT researchers plan to observe Andromeda for 200,000 seconds this July, using a detector less precise in locating star positions but more precise in determining the energies of the X-rays emitted.

In anticipation of the July observations, Eugene A. Magnier of MIT and his colleagues are analyzing Andromeda images made in visible light with the 1.3-meter telescope at the Michigan-Dartmouth-MIT Observatory near Tucson, Ariz. They hope to identify visible-light counterparts for many of the X-ray sources that astronomers expect ROSAT to find.
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Title Annotation:Andromeda galaxy's core may mimic our own galaxy's core
Author:Cowen, Ron
Publication:Science News
Date:Jun 8, 1991
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