Erratum: Inspiral into Gargantua (Class. Quantum Grav. (2016) 33 (155002) DOI: 10.1088/0264-9381/33/15/155002)

Our analysis of the change in black hole spin during near-horizon inspiral (section 2.3) was incorrect due to a computational error. The affected equations are (23) (25), which we repeat here: (Equation presented) It is more convenient to present the corrected results in terms of ∈² = 1 - (a/M)² ≈ 2 (1 - a/M), where ∈ ≪ 1. Using the same method described in the text and fixing the computational error, we instead find (Equation presented) The most important difference is that the change in spin is now linear in the mass ratio, as opposed to quadratic. Note also that the new left-hand-side of (25) now correctly refers to the absolute value of a/M, which is necessary since a/M decreases during near-horizon inspiral. We thank Geoffrey Comp re for pointing out these errors see also reference [1]. The change in spin over the near-horizon inspiral is significantly larger than originally calculated, meaning that there is a smaller range of mass-ratios over which the near-horizon inspiral can occur (without spinning down the black hole such that the near-horizon region no longer exists).We may estimate this range based on the observation (section 3.1) that nearhorizon inspiral is visible in the waveform for a ≳ 0.9999M with a starting radius of X₀ ≈ 0.3. Demanding Δ|a/M|total < 0.0001 using X0 = 0.3, the new version of (25) gives the bound μ/M < 0.025. Thus near-horizon inspiral remains consistent for both the LIGO and LISA sources discussed in the appendix (with mass ratios of order 10-3 and smaller), and our main conclusions about observability are unmodified.