Because the galaxies are so far away, their light is often pretty dim, so what scientists do is basically leave the camera going for a long time. Think to if you've ever taken a picture in a dim setting, like outdoors in the evening. If you turn the flash off, you can get a decent picture, but lots of times that picture is blurry. This is because your camera leaves the shutter open for a longer time than in a bright setting to collect more light. Since the shutter is open a long time, any movement you make is captured and results in a blurry image!

Luckily for us, galaxies don't really move in the amount of time we take pictures of them! It is fairly common to point a camera at a galaxy for 20 minutes to get a long exposure! Even then, somegalaxies are so faint, that astronomers have to take lots of pictures and then basically add them all together to get even more total light from the galaxy. This is how many astronomy photos are made.

Thanks for the question!

-Randi