NGC 4038
NGC 3166 & 3169 - The Disturbed Galaxy Duo
This pair of galaxies is definitely disturbed. They lie in the direction of Sextans, the constellation named for an astronomical instrument invented by Johannes Hevelius in 1687. The larger of the two galaxies (lower right) is NGC 3169. It was and still is a spiral galaxy with clearly defined spiral arms, however the arms are being pulled on by the nearby galaxy NGC 3166 (upper left). This gravitational tug-of-war has affected both galaxies substantially, hence the unnofficial name The Disturbed Galaxy Duo. Looking closely at NGC 3169, you can see fainter cloudy material all around it; this material is actually billions of stars so far away that they do not resolve into points of light. Another observation about NGC 3169 is the possibility that a previous galaxy has already collided with it and passed through it many times to create dozens of cloudy trails before finally being absorbed completely. The blue area along the spiral arms indicate the formation of many new young stars.
NGC 3166 (again upper left) is a barred spiral galaxy with a small bright nucleus within which the short bright bar is visible. It is less blue than NGC 3169, and therefore is not in a phase of considerable star formation.  At the far top left is a third likely associated galaxy, NGC 3165, and at the middle right is very faint 16 magnitude eliptical galaxy PGC 29873, both which appear undisturbed. All four galaxies are in the galactic group Leo 1 Group and are embedded in an extend ring of neutral hydrogen (not visible) centered on NGC 3169.  The entire group is between 60 and 75 million light years away from us.  The stats on NGC 3169 are: RA 10h 14m 15s, Dec +03° 27' 58", Mag: 10.3, Size 4.2'x2.9', and Class SA(s)a pec.
Optics: RC Optical System 20" F/8.2 (4165.6 mm Focal Length) Date: Dec 2017 - Jan 2018
Camera: SBIG STXL-11000 with Adaptive Optics AO-X Location: Columbus, Texas
Exposure: LRGB = 430:80:70:80 minutes Imager: Kent E. Biggs