This question on the world building site sparked my curiosity on whether we could see signs of an intergalactic civilization. The question itself effectively asks whether this is possible for our own galaxy. Since the Milky Way is 100 lightyears across, and assuming there is an alien self replicating machine capable of traveling at 1% of c, then it would be able to colonize the whole galaxy in about 10mn years give or take. This is a tiny amount of time in the grand history of the universe so it's at least plausible.
However when you extend this thought to intergalactic distances it quickly becomes unfeasible. The distance to the Andromeda galaxy is 2mn light years and the width of the local supercluster is 110mn. Travelling these distances at 1% c would take the entire age of the universe...
So on to my question: is it possible to achieve anything close to 80% of the speed of light using gravitational assistance from the black holes orbiting the center of our galaxy?
I don't know in detail how gravity assists work so I have no idea what the limiting factors are, but let's assume we have millions of years to time it out and a delta v budget of 1% the speed of light.
Since the boost depends on the proximity to the boosting body I assume the biggest hurdle would be the acceleration you would have to endure as you get closer to the blackhole boosters. Is there an easy way to estimate what it would take?
Some napkin math tells me it's somewhat plausible:
- The diameter of the black hole at the center of our galaxy is on the order of a light minute.
- It takes on the order of 10 minutes accelerating at 50000g to get to the speed of light.
- Accelerations on the order of 50000g were achieved by the rail gun prototypes. Since there are some proposals to add electronic chips to rail gun projectiles, I'll assume our autonomous alien friends have the tech to withstand this.