Atlas Image mosaic, covering 11.0´ × 11.0´ on the sky, of Messier 27 (M27), the Dumbbell Nebula (also known as NGC 6853). This famous large planetary nebula glows ghostly red through this crowded star field. Its distance from us is not well known, but is likely between 150 pc (490 light years) and 1100 pc (3500 light years). The main body of the nebula covers about 6´, but the nebula's fainter halo covers about 15´. Optically, the Dumbbell is one of the brightest planetary nebulae. Its appearance and brightness in the 2MASS near-infrared image is significantly different than in the optical. The red color seen in the 2MASS image is due to excited molecular hydrogen, H₂ (Zuckerman & Gatley 1988, ApJ, 324, 501), which emits strongly at 2.12 µm in the 2MASS K_s band. Planetary nebulae are formed as low-mass stars, like our Sun, reach the end of their lives and lose their outer envelopes to the interstellar medium. Image mosaic by S. Van Dyk (IPAC).

Atlas Image mosaic, covering 10.0´ × 10.0´ on the sky, of the Chamaeleon infrared nebula (IRAS 11072-7727), which is a bipolar reflection nebula in the Cha I dark cloud. The nebula is at a distance from us of about 190 pc (619 light years). Feldt et al. (1998, A&A, 332, 849) recently imaged the nebula in the near-infrared. They describe the nebula as outlining two parabolic cavities excavated by outflow activity. The overall morphology of the nebula in the near-IR provided Feldt et al. with evidence that the bright source at the center contains a tilted disk surrounding a very young binary star system. Image mosaic by S. Van Dyk (IPAC).

Atlas Image mosaic, covering 13.0´ × 13.0´ on the sky, of the compact open cluster Westerlund 1. The cluster is located in the southern Milky Way in Ara and is heavily reddened, behind nearly 13 magnitudes of visual extinction (Piatti, Bica, & Claria 1997, A&AS, 127, 423), making it one of the most reddened known open clusters in the Milky Way Galaxy. Piatti et al., from optical photometry, determined that this massive cluster is at a distance of about 1.1 kpc (nearly 3600 light years), contains several intrinsically luminous stars, and has an age of about 8 Myr. Image mosaic by S. Van Dyk (IPAC).

Atlas Image mosaic, covering 8.3´ × 17.1´ on the sky, of the Circinus Galaxy. This spiral galaxy, in the constellation Circinus, is relatively nearby, at only 4 Mpc (13 million light years), and is seen through a window of low extinction (only about 1.5 visual magnitudes) near the Galactic Plane. Observations in the optical, X-rays, and radio indicate that Circinus has a Seyfert 2 nucleus, that is, the galaxy is harboring a supermassive black hole at its center. Storchi-Bergmann et al. (1999, MNRAS, 304, 35) find from near-infrared spectroscopy of the nucleus evidence for an aging starburst. A dark dust lane, running to the south and east of the nucleus, is apparent in the 2MASS image; the disk of the galaxy, overall, is much fainter than the bright nucleus. Maiolino et al. (2000, ApJ, 531, 219) propose, based on Hubble Space Telescope near-infrared NICMOS imaging, that this dust lane traces a nuclear gas bar that may be responsible for feeding the active nucleus; their imaging indicates that star formation in the nuclear region is still ongoing, as gas flows inward to the black hole, and points to a complex nuclear star formation history. Image mosaic by S. Van Dyk (IPAC).

Atlas Image mosaic, covering 0.70° × 0.90° on the sky, of the Carina (Keyhole) Nebula. This spectacular region of the Milky Way Galaxy, also known as NGC 3372, contains an unusually high concentration of young massive stars, many located in star clusters, at about 2300 pc (7500 light years). The region is the result of a burst of star formation ~3 Myr ago. Star formation in this region is still ongoing! The truly phenomenal star Carinae, a luminous blue variable star which experienced an enormous outburst in 1843, is the bright star toward the southeast of the nebula. This star, seen surrounded by the amazing double-lobed structure of the Homunculus at high spatial resolution by the Hubble Space Telescope, is one of the most massive stars in the Galaxy, at over 100 times the mass of the Sun (Davidson & Humphreys 1997, ARA&A, 35, 1). ( Car in the 2MASS image shows a persistence artifact that trails due north of the star; the artifact shows this known double-lobed structure of the Homonculus as well.) Car is part of star cluster Trumpler 16. Another very rich cluster of massive stars is Trumpler 14, in the nebula toward the northwest. The nebula, as seen by 2MASS, is a complex mixture of molecular gas, reflected starlight, and dust. Within the large dark patches and tendrils of dust are new, obscured young stars still forming in this large cloud. N.B.: The full mosaic is a very large file: 6.6 Mb! Image mosaic by E. Kopan (IPAC). Featured as an Astronomy Picture of the Day!

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