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Why Don’t All Objects in the Milky Way Rotate Around the Black Hole at the Center of our Galaxy?

-- Courtney | April 26, 2020

Question:

If the stars in the milky way orbit the super massive black hole/s in the middle of the Milky Way, then why do the planetary bodies orbiting stars not get caught in the stronger orbital field that the stars are caught in? how does the weaker gravity of the star override the gravitational force at work on the star itself? the same could be said for moons and the theoretical moons of moons etc

-- Courtney

Answer:

The gravitational force has a distance dependence to it that makes it decrease as you get further away from an object. This applies to the black hole at the center of our galaxy, so that its gravitational influence is limited to just the immediate region around the center of our galaxy. This is why all objects in our galaxy are not rotating around that black hole at the center of our galaxy, but are instead affected by objects, like stars and planets, that are more nearby. But why then does our galaxy rotate? The answer to that question is that when our galaxy formed from a giant gas cloud it started spinning, and this residual spin is what we measure as the rotation of our galaxy. For more details see the nice description, including a mini tour of our galaxy, on the Universe Today description of our Milky Way’s general properties.

-- Jeff Mangum

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