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Central Cluster of NGC 3603
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Central Cluster of NGC 3603

April 26, 2005
NGC 3603 is located in the Carina spiral arm in the Milky Way galaxy at a distance of about 20,000 light-years (6 - 7 kpc). It is the only massive, galactic "HII-region" (so denoted by astronomers because part of its hydrogen is ionized) in which a central cluster of strongly UV-radiating stars of types "O" and "B" that ionize the nebula can be studied at visual and near-infrared wavelengths. This is because the line-of-sight is reasonably free of dust in this direction; the dimming in near-infrared radiation due to intervening matter between the nebula and us is only about a factor of 2 (contrary to 80 in visible light).

The total mass of the hot O- and B-stars in NGC 3603 is over 2000 solar masses. Together, the more than fifty heavy and bright O-stars in NGC 3603 have about 100 times the ionizing power of the well-known Trapezium cluster in the Orion Nebula. In fact, the star cluster in NGC 3603 is in many respects very similar to the core of the large, ionizing cluster in the approx. eight times more distant Tarantula Nebula in the LMC.

The central cluster is the densest concentration of massive stars known in the Milky Way (this area is enlarged in this photo ; the field shown is about 2.5 x 2.5 light-years2). It hosts more than 50 hot O-type stars. The brightest star in the field is the red supergiant IRS4; it is located about 80 arcsec NE of the center. About 18 arcsec N of the center are the ring nebula and the bipolar outflows around the blue supergiant Sher25. The photo also shows three proplyd-like objects that have been recently discovered; they are similar to those seen in Orion Nebula, but 20-30 times more extended. About 1 arcmin SSE of the central cluster are seen the brightest members of the deeply embedded proto cluster IRS9.


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