At "7 O'Clock" on the galaxy image there is a lensing event, a circle of arcs surrounding a black area with no visible object at the centre. I do not think that this is an artifact of the imaging but a real lensing event. Please investigate further. (No pun intended).
by Budgieye moderator
Probably an artifact. There was probably a cosmic ray hit on the ccd chip, making a mess. The software circles the mess, removes the hit, then tries to smooth everything over in the hope that nobody will notice.
These images are taken apart and put back together in an alarming way. see http://www.sdss3.org/dr8/software/idlutils_doc.php#CR if you are a computer type person which I am not.
In dr7 images, we used to see more of them. http://www.galaxyzooforum.org/index.php?topic=276103.msg368791#msg368791
The software in dr8 removes more of them, but sometimes it may start removing starburst areas too.