Wysocki-Kick Inference

LIGO has detected and inferred the parameters of several binary black holes. Using these inferences, we can compare LIGO’s observations to the predictions of detailed formation models. These models attempt to explain the number of sources LIGO detects, and the likely properties (masses, spins) of each event. In a recent series of papers, we perform these comparisons, between LIGO’s first four observations (GW150914, GW151226,GW170104, and LVT151012) and detailed models for BH-BH formation from isolated pairs of stars.

Most successful formation scenarios can reproduce the correct number and even approximate mass distribution of sources LIGO observes. As I explained years ago in several talks and in Mandel and O’Shaughnessy (2010), to distinguish between formation channels, we must use the observed BH spins, whose magnitude and (critically) misalignment can provide clues about how each pair of BHs formed.

We find LIGO’s observations can be easily explained by isolated binary evolution, by adopting one of two simple possibilities. One possibility, as described in Belczynski et al 2017, is that massive BHs may have small spins. Most of LIGO’s observations to date are consistent with zero spin; only one binary black hole, the lightest, has definite evidence for at least one nonzer spin. Another possibility is that BHs, at birth, are ``kicked”, tilting the orbit and reducing the net aligned spin to which LIGO is sensitive.

For experts: We compare the inferred masses and spins of LIGO’s observed black holes to models for isolated binary evolution, systematically exploring the impact of BH natal kicks. We consider a wide range of BH natal spin distributions. Isolated binary evolution can easily reproduce LIGO’s observations, even when allowing a significant chance of large natal spin, simply by adopting very modest BH natal kicks. Conversely, as seen in other studies, LIGO’s observations suggest that BH natal spins are likely small. This study generalizes the work of ROS, Gerosa and Wysocki, by applying detailed binary evolution models.

For more information, see

• Wysocki et al Explaining LIGO’s observations via isolated binary evolution with natal kicks, available at arxiv.org

• Belczynski et al GW170104 and the origin of heavy, low-spin binary black holes via classical isolated binary evolution, available at arxiv.org

• ROS, Gerosa, Wysocki, “Inferences about supernova physics from gravitational-wave measurements: GW151226 spin misalignment as an indicator of strong black-hole natal kicks” (PRL 119, 011101)