Illuminating Black Hole Binary Formation Channels With Spins in Advanced Ligo

Abstract

The recent detections of the binary black hole mergers GW150914 and GW151226 have inaugurated the field of gravitational-wave astronomy. For the two main formation channels that have been proposed for these sources, isolated binary evolution in galactic fields and dynamical formation in dense star clusters, the predicted masses and merger rates overlap significantly, complicating any astrophysical claims that rely on measured masses alone. Here, we examine the distribution of spin-orbit misalignments expected for binaries from the field and from dense star clusters. Under standard assumptions for black hole natal kicks, we find that black hole binaries similar to GW150914 could be formed with significant spin-orbit misalignment only through dynamical processes. In particular, these heavy-black hole binaries can only form with a significant spin-orbit anti-alignment in the dynamical channel. Our results suggest that future detections of merging black hole binaries with measurable spins will allow us to identify the main formation channel for these systems.

Dissipative Evolution of Unequal-mass Binary–single Interactions and Its Relevance to Gravitational-wave Detections

“…Together with the spin distribution (e.g. Rodriguez et al 2016c;Kushnir et al 2016;Zaldarriaga et al 2017), the eccentricity distribution is expected to play a key role in constraining the origin of BBH mergers observable by LIGO and next generation GW observatories (e.g. Chen & Amaro-Seoane 2017).…”

Distinguishing spin-aligned and isotropic black hole populations with gravitational waves

“…One signature of such environments is the angular distribution of the black hole spins. Binary systems that formed through dynamical interactions between alreadycompact objects are expected to have isotropic spin orientations [5][6][7][8][9] (that is, the spins of the black holes are randomly oriented with respect to the orbit of the binary system), whereas those that formed from pairs of stars born together are more likely to have spins that are preferentially aligned with the orbit [10][11][12][13][14] . The bestmeasured combination of spin parameters 3,4 for each of the four likely binary black hole detections GW150914, LVT151012, GW151226 and GW170104 is the 'effective' spin.…”

“…The spin directions of binary black holes that are formed dynamically through interactions in dense stellar environments [5][6][7][8] are expected to be isotropic, owing to the absence of a preferred direction 9 and the persistence of an isotropic distribution throughout in-spiralling 29,30 . Online Content Methods, along with any additional Extended Data display items and Source Data, are available in the online version of the paper; references unique to these sections appear only in the online paper.…”

Rapidly Rising Optical Transients from the Birth of Binary Neutron Stars

“…The spin evolution of compact binary progenitors is imprinted in the spin parameters of merging binary black holes, which can also be measured through gravitational-wave detections Abbott et al (2016). Such measurements will shed lights on various questions on the formation scenario of compact binary objects that have been golden candidate sources of gravitational waves (Kushnir et al 2016;Rodriguez et al 2016;Zaldarriaga et al 2017;Hotokezaka & Piran 2017).…”