Why do stars in the disk of a spiral galaxy orbit in roughly the same direction, in the same plane in space?
A)The gas that formed the stars was shaped as a giant, rotating disk.
B)Collisions between the stars caused their motions to organize into a general, spinning disk direction.
C)After the stars formed, gravity pulled the stars down into a plane in space, all orbiting a supermassive black hole.
D)It is pure coincidence; the stars just happen to be going in the same direction.

Question

Quizplus · Accepted Answer

The gas that formed the stars in a spiral galaxy was shaped as a giant, rotating disk. As this disk collapsed to form stars, their motions were also confined to the plane of the disk, leading to a common direction of rotation. Additionally, the gravitational influence of other nearby galaxies can also affect the orientation of the spiral galaxy's disk.

Why Do Stars in the Disk of a Spiral Galaxy