3 Stages of a Binary Merger

The qualitative evolution of NS-NS mergers, or indeed any compact binary merger, has long been understood, and may be divided roughly into inspiral, merger, and ringdown phases, each of which presents a distinct set of challenges for numerical modeling and detection. As a visual aid, we include a cartoon summary in Figure 2View Image, originally intended to describe black hole–black hole (BH-BH) mergers, and attributed to Kip Thorne. Drawn before the advent of the supercomputer simulations it envisions, we note that merger waveforms for all compact binary mergers have proven to be much smoother and simpler than shown here. To adapt it to NS-NS mergers, we note that NSs are generally assumed to be essentially non-spinning, and that the “ringdown” phase may describe either a newly formed BH or a NS that survives against gravitational collapse.

View Image

Figure 2: Cartoon picture of a compact binary coalescence, drawn for a BH-BH merger but applicable to NS-NS mergers as well (although NSs are generally assumed to be non-spinning). Image adapted from Kip Thorne.

Summarizing the evolution of the system through the three phases:

 3.1 Comparison to BH-NS mergers
 3.2 Qualitative numerical results

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