NGC5139 Omega Centauri, Centaurus
Astro-Physics 155 EDF (155TCC) f/5.4 refractor
KAF-16803; FLI Proline
Total Exposure Time: 4.6+ hours; LRGB 115:55:55:55 minutes, unbinned
February 2009; RDO, Moorook, AU
Comments: This is the biggest of all globular clusters in our Milky Way galaxy. With its about 5 million solar masses, it is about 10 times as massive as other big globulars, and has about the same mass as the smallest whole galaxies. It is also the most luminous Milky Way globular, and the brightest globular cluster in the sky. In the Local Group, it is outshined only by the brightest globular cluster G1 in the Andromeda Galaxy M31. In 1999, a team led by Young-Wook Lee of Yonsei University, South Korea, obtained a color-magnitude diagram (CMD) for 50,000 member stars of Omega Centauri with the 0.9-m telescope of CTIO in Chile. Studies of this CMD indicate that the stars of this cluster did not all form at once but over a 2-billion-year period of time, with several starburst peaks. This was the first time that multiple populations were found in a globular cluster. The team who carried out this work speculates that this result may indicate that Omega Centauri might be the remnant of a nucleus of a small galaxy which has merged with our Milky Way (Ref). Here is a cropped version showing a closer view of the cluster.
Interestingly, there is faint dust or flux nebulosity in this region that I haven't seen before in any image. I suspect that it gets processed out. This dust is in the lower right portion of the image. It is very faint and can be seen if you look at the screen from the right side instead of directly in front. It really is there! Here is a version showing the right lower quandrant of the original image decolored and inverted. You can see the dust better -- very faint!