### What happens if you fail to reach escape velocity for the galaxy?

• I was listening to Skeptics Guide to the Universe the other day, and Steve Novella mentioned that the escape velocity for the galaxy is 544 km/s.

If an object fails to reach escape velocity on Earth, it will return to Earth. What will be the fate of an object, say the Voyager spacecraft which is currently traveling at 17 km/s, that fail to meet the 544 km/s.

I'm having a hard time wrapping my head around what galactic escape velocity means.

Does this mean that Voyager is incrementally slowing down by the pull of the galaxy? Given enough time, will it end up in the supermassive black hole in the center?

Escape velocity is simply the speed at which an objected placed at infinity, and acting only under the influence of gravity from a second object, will collide with that second object. Objects launched at less than that velocity will inevitably return to that second obeject, unless gravity or some other force intervenes.

8 years ago

If you fail to reach escape velocity from the earth, you won't break free of its gravitational well, in other words, you will keep orbiting the center of mass of the earth. If the path of your orbit intersects the surface of the earth, then you will, you know, crash.

If you fail to reach escape velocity for the galaxy, you'll keep orbiting the center of mass of the galaxy, just like the other couple hundred billions of stars in the galaxy. The galaxy has no hard surface to crash into, so you'll keep orbiting until you come close enough to another orbiting body to perturb your orbit (which could, in the right circumstances, leave you with escape velocity and kick you out of the galaxy.