Distance: 16,000 Light Years
Size: 36.3 Arc Minutes
Age: 12 Billion Years
Telescope: Takahashi TOA-130
Camera: QSI 683
Mount: AP 900
Exposure: L 20×60 Bin 1, RGB 20×30 Bin2
NGC 5139 is a globular cluster in the constellation Centaurus. It is the largest globular cluster in our galaxy at 36.3 arc minutes in size which converts to 150 light years across. It is also the brightest globular cluster in our Milky Way galaxy and contains about 10 million stars. I was trying to visualize what the sky would look like from a star inside of this cluster and I found a link to a NASA pdf that gave this explanation:
“All of the stars in the image are cozy neighbors. The average distance between any two stars in the cluster’s crowded core is roughly 13 times closer than our sun’s nearest stellar neighbor, Alpha Centauri. Although the stars are close together, WFC3 can resolve each of them as individual stars. If anyone lived on this globular cluster, they would behold a star-saturated sky that is roughly 100 times brighter than Earth’s sky.”
NGC 5139 contains many types of stars at varying stages of development. This indicates many levels of star formation occurring over a few billion years. One possible explanation for this is that NGC5139 is a captured system from another dwarf galaxy. This is supported by a retrograde motion of the cluster and all stars in the cluster have the same proper motion, rotation, and average radial velocity. Typical of most globular clusters, the Omega cluster contains blue stragglers and variable stars. In addition, there are stars along the main sequence like our own sun and red giants.
This cluster has been a goal of mine for the 3 years that I have been imaging. It sits very low in the sky from 34 degrees latitude and is only visible here for about a month. I was very pleased when I slewed to the target and there was a cluster in my field of view! The only problem was that there was a pipe I use for a wind screen that ran right through the frame. The pipe is permanent and I did not want to cut it to get the shot. I think this is what caused the strange shapes of some of the brighter stars. This cluster was captured in one sitting at a dark sky site with a SQM of 20.69. The conditions were excellent with a clear sky, a temperature of 65F, and humidity at 50%. I was surprised how much was revealed with 60 second exposures.