Magnetic reconnection is invoked because it can produce extreme speeds, on the order of .1 C.
A fission or fusion bomb produces an explosion at speed .05 C.
A spinning black hole drags space around with it, and this amplifies the Oberth effect.
You can extract energy from a spinning black hole without sacrificing mass to the hole.
These are "Kerr black holes".
LIGO results show that black hole mergers almost always produce a hole that is rapidly spinning, on the order of 70% of maximum. The universe is all Kerr black holes.
This trick is equivalent to the Oberth maneuver for rockets. It's good to draw attention
to the Oberth maneuver because it will be the chief tool for moving around the solar system.
Suppose you're in space and you fire a rocket, producing a speed change of V.
If you instead arrange to skim a planet and fire the rocket at the moment of closest
approach to the planet, then the resultant speed change (after you depart the planet) is larger than V.
This is the prime maneuver for traveling around the solar system.
The gravity assist is also useful, and it's independent from the Oberth maneuver.