Milky Way stars are not orbiting the black hole Sagittarius A* in the center of the Milky Way galaxy.
Betcha you didn't know this.
This is the biggest misconception in astronomy.
What's going on then? Why are the stars moving in circles around the central black hole?
Spoiler alert:
In the Solar system planets orbit the Sun because the Sun is 99.86% of the system's mass. That concentrates gravity in one single central point.
For the Milky Way, the opposite is true: Sagittarius A* accounts for less than 0.0003% of the galaxy's total mass. The black hole only dominates the gravity of stars within its immediate neighborhood—roughly the inner few light-years.
What are stars actually orbiting?
Stars orbit the combined center of mass (barycenter) of all the matter inside their orbit.
As our Sun orbits the galaxy every ~230 million years, it isn't being pulled by Sagittarius A*. Instead, it is being pulled by the collective gravity of tens of billions of stars, interstellar gas clouds, and dark matter located between us and the center of the galaxy.
If you vanish Sagittarius A* from existence in an instant, stars like our Sun would not notice any gravitational change and would continue on their exact same path around the galaxy. Only the handful of "S-stars" whipped around in tight, immediate orbits around the black hole would fly off into deep space.
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