Searching for a Black Hole in the Outer Solar System

TL;DR

This paper explores methods to detect a potential primordial black hole in the outer Solar System, proposing spacecraft-based gravitational measurements as a way to identify it if conventional searches fail.

Contribution

It introduces a novel approach using laser-launched spacecraft to detect a black hole in the outer Solar System through precise gravitational measurements.

Findings

Spacecraft can reach 500 AU in about a decade at 0.001c.

Timing measurements with 10^{-5} s accuracy can reveal the black hole's gravitational influence.

This method offers an alternative to telescopic searches for non-conventional objects.

Abstract

There are hints of a novel object ("Planet 9") with a mass $5-10$ $M_\oplus$ in the outer Solar System, at a distance of order 500 AU. If it is a relatively conventional planet, it can be found in telescopic searches. Alternatively, it has been suggested that this body might be a primordial black hole (PBH). In that case, conventional searches will fail. A possible alternative is to probe the gravitational field of this object using small, laser-launched spacecraft, like the ones envisioned in the Breakthrough Starshot project. With a velocity of order $.001~c$, such spacecraft can reach Planet 9 roughly a decade after launch and can discover it if they can report timing measurements accurate to $10^{-5}$ seconds back to Earth.