Using Neutron Stars To Accelerate Large Masses

[PatrickPowers]

https://arxiv.org/pdf/1903.03423

A clever idea.

Gravitational slingshots around a neutron star in a compact binary have been proposed as a means
of accelerating large masses to potentially relativistic speeds. Such a slingshot is attractive since fuel
is not expended for the acceleration, however it does entail a spacecraft diving into close proximity
of the binary, which could be hazardous. It is proposed here that such a slingshot can be performed
remotely using a beam of light which follows a boomerang null geodesic. Using a moving black hole as a
gravitational mirror, kinetic energy from the black hole is transferred to the beam of light as a blueshift
and upon return the recycled photons not only accelerate, but also add energy to, the spacecraft. It is
shown here that this gained energy can be later expended to reach a terminal velocity of approximately
133% the velocity of the black hole. A civilization could exploit black holes as galactic way points
but would be difficult to detect remotely, except for an elevated binary merger rate and excess binary
eccentricity.