Inferring spin tilts of binary black holes at formation with plus-era gravitational wave detectors

Understand

The spin orientations of spinning binary black hole (BBH) mergers detected by ground-based gravitational wave detectors such as LIGO and Virgo can provide important clues about the formation of such binaries.

• However, these spin tilts, i.e., the angles between the spin vector of each black hole and the binary's orbital angular momentum vector, can change due to precessional effects as the black holes evolve from a large separation to their merger.
• The tilts inferred at a frequency in the sensitive band of the detectors by comparing the signal with theoretical waveforms can thus be significantly different from the tilts when the binary originally formed.
• These tilts at the binary's formation are well approximated in many scenarios by evolving the BBH backwards in time to a formally infinite separation.