From yesterday’s Astronomy Picture of the Day: The View Near a Black Hole:
I’ve got this one set as my desktop background. Though a black hole itself is invisible, its powerful gravity sucks in gases from surrounding space. These gases become extremely hot as they spiral into the black hole, emiting x-rays and other electromagnetic radiation in the process.
Grace and Peace
GeoChristian 
Take off your geology hat and put on your astronomy hat. I know this is an artists conception, but there seems (in real photographs of things like galaxies – at least spiral ones) to be a common “flat” formation of stuff. Why is that? Why is the Milky Way “flat” (I know it’s light years thick, but it’s relatively flat)?
I assume things are relatively flat on earth because of gravity, but gravity in space pulls in from all sides equally, right? So why are there flat formations?
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Basic collisions and gravity pulling between objects.
Imagine two disks of dust and debris orbiting around something at an angle with each other. They would collide with each other, knocking each other apart. Even if they weren’t passing through each other, they would pull each other apart with gravitational pull too.
Most things in the galaxy are not at rest in respect to each other – typically they are moving thousands or even hundreds of thousands of of meters per second in relation to each other.
So, as gas from a nearby star (or just the passing dust/gas in an area of the galaxy) is caught be the gravitational pull of something (such as a star or black hole), it already has a specific direction which is bent and pulled by the gravitational tug of the star or black hole.
That gives it the motion which leads to the orbiting, disk-like pattern we see in galaxies, solar systems, and accretion disks around black holes.
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Hmmm, looking back on that, I could probably clarify a couple of those statements. It might be easier if I were able to draw some pictures representing the gravitational pull on passing objects and how it affects them.
Suffice it to say that if you have something large moving through a cloud of smaller objects (gas/dust/asteroids), their relative motions will form a disk of the small stuff orbiting the big thing.
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