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Mapping new features of Milky Way's bulge.

Mapping new features of Milky Way's bulge

With their view already obscured by Earth's atmosphere, astronomers have a tough time peering through galactic dust for a penetrating look at the Milky Way's core. But in 1985, the Infrared Telescope (IRT) headed past the atmospheric shroud and took its pictures from space. Flown on the shuttle, it returned with enough data to provide a detailed map of our galaxy's inner bulge.

While the IRT images are limited to one wavelength and equal the resolution of pictures so far obtained by the Cosmic Background Explorer (SN: 4/28/90, p.260), they capture a greater slice of the Milky Way in the northern celestial hemisphere. An already established calibration between detected light signals and their intensity enabled Stephen M. Kent and his co-workers at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., to compare IRT's Milky Way maps with images of similar spiral galaxies that appear face-on as viewed from Earth. Such comparisons, says Kent, "can help fill in the missing blanks" about galactic structures, hinting at the three-dimensional character of Milky Way features visible only edge-on when viewed from Earth's vicinity.

Kent and his colleagues find evidence that gas in the Milky Way's inner bulge -- about 3,300 light-years in diameter -- may move in an elliptical orbit, indicating the bulge is much less symmetric than previously thought. He notes that the bulges of other spiral galaxies, including the nearby M31, also show asymmetry. In addition, Kent says the work supports the notion that a star cluster exists just a few light-years from the galactic center. Several scientists have suggested that such a cluster, also seen near the center of other spiral galaxies, may be caused by a black hole lurking at the Milky Way's core.

The team also discovered clues to a Milky Way feature that has no obvious counterpart in other spiral galaxies: an apparent ring of stars about 13,000 light-years from the center. Kent believes this may be an edge-on view of one of the Milky Way's spiral arms.

He and his co-workers, who discussed their initial findings at a conference in Chile last year, are preparing an expanded report for publication.
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Author:Cowen, Ron
Publication:Science News
Date:Jun 2, 1990
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