NGC 2808: Globular Cluster Now--But Once a Dwarf Galaxy's Core!Equipment:OTA: CDK24
Camera: QHY 600
Pixel Resolution: 0.39” (downsampled 2x)
Observatory: Telescope Live
Date of Capture: 03-24
Date of Processing: 12-24
Exposures Used:Broadband: 2.7h
Narrowband: 0
Subframes Discarded: 10%
Image Width: 0.51deg
Processing Tools:1. Commercial: PixInsight, Topaz, Radiant Photo, PhotoDirector, 3DLUT Creator, AKVIS
2. Pixinsight Addons: NoiseXTerminator, BlurXTerminator, StarXTerminator
3. My Scripts: NB_Assistant, AC_Restar, Subframe Weighting Tool (w/ J. Hunt), ColorTweaker, StarTweaker
(image processed on HDR monitors)
Target Description: (Wikipedia, etc.)
The general wisdom once held that globular clusters can contain only one generation of stars. Because of their compactness, the strong solar winds disperse the cluster’s gas when that first generation forms and no further stars can condense. However, a second generation can arise as those first stars die and repopulate the cluster with their gases. Such 2-generation GCs are now widely identified. Fine, but this cluster has been found to have not one, not two, but three generations of stars (
Piotto, et al., 2007). One explanation for this is that NGC 2808 is the core of a dwarf galaxy, the hypothetical galaxy often referred to as the “Gaia Enceladus,” which is estimated to have collided with our Milky Way galaxy about 8-11 billion years ago and added 8 globular clusters and about 50 billion solar masses.
How do astronomers infer that such a dwarf-swallowing event ever occurred? They observe a subset of Milky Way stars that do not have the usual circular orbits around our galaxy’s center but have highly elliptical orbits, as if they came from outside the galaxy…as they probably did.
NGC 2808 has over a million stars; that’s abnormally large for a globular cluster and led to the interpretation that it is a galactic core, not just another GC. The orbit of this GC is also highly eccentric and has a gravitational tail(!); conclusive evidence is that it is alien to our galaxy.
Processing Description:The processing followed a simple path, especially because the GC’s center is extremely dense (see above) and not resolvable with the telescope used.
Target Statistics:Distance: 31.3 ly
Apparent Magnitude: 6.2
Alex Woronow 
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