Originally posted by Raabjorn
Accoarding to one of the articles the whole galaxy spins around this center black hole, so we must be getting closer and closer? At the same time this
black hole must be getting an ever increased mass sucking every star in the galaxy closer and closer at an accelerating pace.
No, galaxy
doesn't rotate around this black hole, it rotates around it's center of mass.
Just same way like (objects in) solar system.
Also that mass was there even before black hole.
And like in our solar system, orbits of objects are in balance between force of gravity and "centrifugal force". For object to make its orbit
smaller it has to somehow reduce it's orbital energy (speed), like decrease speed so that force caused by gravity becomes bigger and causes it to
fall to smaller orbit until balance is gained. (which happens if object doesn't lose its orbital energy continuously) Same applies to whole galaxy,
rotation of matter keeps it from falling toward center of mass (and gravity) unless some force slows that rotation.