Whahahahahahahahahahahahahahahahaha hahahahahahahahahaha!!!!!!!!!!!!!
Looks like you have a internal galaxy in your equipment.
I am jealous, give it to me pls.
All joking aside , it does look like an galaxy.
However, i have had that kind of picture too in registax and that happened when i substracted a darkframe.
So if you are using registax then something like this could happen.
Or it is a nice way of registax to tell you that you have done something wrong.
? darks from my flats ? Aren't you supposed to substract the darks and the flats from the image files?
I just begun imaging but that is the way i have been told to do it.