At the top of this skyscape, Centaurus A (NGC 5128) seems to be a fantastic jumble of old yellow stars, young blue star clusters, and imposing dark dust lanes. Spanning over 60,000 light-years, the peculiar elliptical galaxy is apparently the result of a collision of two otherwise normal galaxies. The left over cosmic debris is steadily being consumed by a black hole with a billion times the mass of the Sun which lies at the center of Centaurus A. It's likely that such black hole central engines generate the radio, X-ray, and gamma-ray energy radiated by Centaurus A and other active galaxies. For an active galaxy Centaurus A is close, a mere 10 million light-years away, and is well-studied by earthbound astronomers. At the bottom of this image, globular star cluster Omega Centauri (NGC 5139) is some 15,000 light-years away and 150 light-years in diameter. Packed with about 10 million stars much older than the Sun, Omega Cen is the largest of 200 or so known globular clusters that roam the halo of our Milky Way galaxy. Though most star clusters consist of stars with the same age and composition, the enigmatic Omega Cen exhibits the presence of different stellar populations with a spread of ages and chemical abundances. In fact, Omega Cen may be the remnant core of a small galaxy merging with the Milky Way (text adapted from APOD). Pentax 67 EDIF 300mm f/4 - FLI Proline 16803 - L (160m) R (40m) G (40m) B (40m) - Warrumbungle Observatory, Coonabarabran, NSW, Australia
What's happening to galaxies NGC 474 and NGC 467? The multiple layers of emission appear strangely complex and unexpected given the relatively featureless appearance of the elliptical galaxy in less deep images. The cause of the shells is currently unknown, but possibly tidal tails related to debris left over from absorbing numerous small galaxies in the past billion years. Alternatively the shells may be like ripples in a pond, where the ongoing collision with NGC 470, the spiral galaxy to the right of NGC 474, is causing density waves to ripple though the galactic giant. Regardless of the actual cause, the above image dramatically highlights the increasing consensus that the outer halos of most large galaxies are not really smooth but have complexities induced by frequent interactions with -- and accretions of -- smaller nearby galaxies. The halo of our own Milky Way Galaxy is one example of such unexpected complexity. NGC 474 spans about 250,000 light years and lies about 100 million light years distant toward the constellation of the Fish Pisces. (Text adapted from APOD). RCOS 14.5" f/9 - APOGEE U16 - L (240m) R (40m) G (40m) B (40m) - Lightbuckets LB003, NM, USA
The small, northern constellation Triangulum harbors this magnificent face-on spiral galaxy, M33. Its popular names include the Pinwheel Galaxy or just the Triangulum Galaxy. M33 is over 50,000 light-years in diameter, third largest in the Local Group of galaxies after the Andromeda Galaxy (M31), and our own Milky Way. About 3 million light-years from the Milky Way, M33 is itself thought to be a satellite of the Andromeda Galaxy and astronomers in these two galaxies would likely have spectacular views of each other's grand spiral star systems. As for the view from planet Earth, this image nicely shows off M33's blue star clusters and pinkish star forming regions that trace the galaxy's loosely wound spiral arms. In fact, the cavernous NGC 604 is the brightest star forming region, seen here at about the 7 o'clock position from the galaxy center. Like M31, M33's population of well-measured variable stars have helped make this nearby spiral a cosmic yardstick for establishing the distance scale of the Universe (text adapted from APOD). TEC 140APO & AP Mach1 - FLI Proline 16803 - Ha (260m) OIII (60m) L (130m) R (25m) G (25m) B (25m) - Gambugliano, Vicenza, Italy
