Do stars revolve as planets do?

Answer 1

If we apply this question to the moon and ask why the moon does not fall to Earth, then we are stating the question that vexed scientists (and others) for centuries until Isaac newton arrived at the Universal Law of Gravitation.

That law says that the force of gravity between two objects is inversely proportional to the square of the distance between them and proportional to the product of the masses of the two objects. The "universal" part of this is that the same law applies to all objects with mass in the universe and applies with the same proportionality constant which we call the gravitational constant, G.

With the force so prescribed, the answer as to the motion of objects is determined by the other three Newtonian laws of motion.

Now, the answer applies to planets around stars and moons around planets and rotating binary stars and even galaxies that are mutually rotating and bound by the force of gravity.

It was Kepler who discovered that the orbits were elliptical but did not know why. Newton calculated the orbits and proved it mathematically.

While it is possible to simply ask "why," it is also possible to answer by saying that to do otherwise would violate the laws of physics. One could ask why the moon doesn't change direction and go backwards occasionally and the answer to that would be that it violated the laws of physics.

Alternatively, one can say that the centripetal force of a planet in circular motion is provided by gravity and is exactly equal to the force required to overcome the effect of inertia tending to keep the body moving in a straight line. (This latter is the apparent force called the centrifugal force.)

If the force of mutual attraction were not an inverse square force, objects would still rotate about there center of gravity, but the result would not necessarily be elliptical or regular. The resulting motion would, however, still satisfy Newton's laws of motion and the force of attraction would still exactly match that require to overcome the inertial tendency of the objects to move in a straight line.

So, because of gravitational attraction planets do not move in a straight line and the deviation from a straight line is caused by gravity and the resulting path is the orbit.

One final caveat is required. The effects of both Special and General Relativity are not taken into account in this answer, but those have no substantial consequence for normal planets and normal stars. Black holes would lead to a more complex situation.

Answer 2

Stars in a galaxy revolve around the center of the galaxy; our sun is part of the Milky Way galaxy and revolves around its center (taking the Earth and other planets with it).