A Robust Test of General Relativity in Space

TL;DR

This paper discusses how space-based gravitational wave detectors like LISA, DECIGO, and BBO can perform robust tests of general relativity's no-hair theorem by observing black hole inspirals, especially involving intermediate-mass black holes.

Contribution

It proposes a more robust method for testing general relativity using early inspiral observations and evaluates the potential of future space missions for these tests.

Findings

Early inspiral observations improve test robustness.

Future missions can perform more stringent tests.

Intermediate-mass black hole inspirals enable precise measurements.

Abstract

LISA may make it possible to test the black-hole uniqueness theorems of general relativity, also called the no-hair theorems, by Ryan's method of detecting the quadrupole moment of a black hole using high-mass-ratio inspirals. This test can be performed more robustly by observing inspirals in earlier stages, where the simplifications used in making inspiral predictions by the perturbative and post-Newtonian methods are more nearly correct. Current concepts for future missions such as DECIGO and BBO would allow even more stringent tests by this same method. Recently discovered evidence supports the existence of intermediate-mass black holes (IMBHs). Inspirals of binary systems with one IMBH and one stellar-mass black hole would fall into the frequency band of proposed maximum sensitivity for DECIGO and BBO. This would enable us to perform the Ryan test more precisely and more robustly. We explain why tests based on observations earlier in the inspiral are more robust and provide preliminary estimates of possible optimal future observations.