A few hours ago, I've taken 178 images of the Eagle Nebula/Omega Nebula area of the milky way using Canon EOS 5D Mark IV, iOptron SkyTracker, and Canon EF70-200mm f/2.8L lens.
As I'll be stacking around 180 shots, I've bumped up the ISO all the way to ISO 32000 and the photos are undoubtably noisy. However, when I was cycling through the photos with my friend, my friend spotted a white dot near the Eagle Nebula in only one shot. It's definitely not noise (see bottom middle towards a little right):
That dot is more than a single pixel, exists in one and only one photo, and has a something-bursting-in-two-directions like shape.
It's obviously not a plane, nor I think it's a satellite.
We are not pros in deep space astrophotography and maybe it's a very simple thing. But just out of curiosity: what is that dot?
UPDATE: I've highlighted the area of interest in the second shot. My settings are: 200mm focal length, 6s exposure, f/4.0, ISO 32000. The photo was taken at location 38.226838, 26.338415 and time 26.09.2017 23:11:34 GMT+3.