1/11/2017 1 Insights in binary black hole formation from gravitational waves Simon Stevenson [email protected] @simon4nine for the COMPAS team Alejandro Vigna-Gómez, Coenraad J. Neijssel1, Jim W. Barrett, Ilya Mandel and more! Melbourne Uni Seminar 1/11/2017 2 Melbourne Uni Seminar 1/11/2017 3 Melbourne Uni Seminar 1/11/2017 4 140 120 100 Maximum total 80 mass against 60 GW170814 metallicity 40 20 0.001 0.01 0.1 1 Adapted from Belczynski+ 2016 arXiv:1602.04531 Melbourne Uni Seminar 1/11/2017 Binary black hole mass distribution 5 Weak constraints on power law Weak evidence for maximum mass around 40 Msol. Pair- instability mass gap? LVC 2016 arXiv:1606.04856 Fishbach & Holz arXiv: 1709.08584 Melbourne Uni Seminar 1/11/2017 Mass function with number of observations Mandel…Stevenson+ 2016 arXiv:1608.08223 Melbourne Uni Seminar 1/11/2017 Binary black hole merger rates 7 § O1 empirically determined merger rates assuming a particular mass distribution § “Power law” distribution favoured over “Flat-in-log” distribution (see next slide) § Lower bounds including GW170104 are 40 and 12 Gpc-3 yr-1 respectively. Remain consistent including GW170814 LVC 2016 arXiv:1606.04856 Melbourne Uni Seminar 1/11/2017 8 How did these binary black holes form? Melbourne Uni Seminar 1/11/2017 9 Formation channels Mandel & Farmer 2017, Nature Melbourne Uni Seminar 1/11/2017 10 § Formation in a dense stellar Dynamical environment such as a globular or formation nuclear cluster Rodriguez+ arXiv:1604.04254 2016 Glasgow Seminar 1/11/2017 11 § Predicted masses and Dynamical spins consistent formation - with observed masses events Carl Rodriguez https://twitter.com/aCarlRodriguez/status/870314010301935618 Melbourne Uni Seminar Adapted from Rodriguez+ 2016 arXiv:1604.04254 1/11/2017 12 Isolated binary evolution Belczynski+ 2016, Nature Melbourne Uni Seminar arXiv:1602.04531 1/11/2017 13 Isolated binary evolution - masses Stevenson+ Nat. Commun. 8, 14906 (2017). arXiv:1704.01352 Updated to include GW170104 Melbourne Uni Seminar (also consistent with GW170814, not shown) 1/11/2017 14 Constrain binary evolution uncertainties with masses and rates Melbourne Uni Seminar 1/11/2017 Uncertainties in binary evolution can be explored with pop synth Stevenson+ 2015 arXiv:1504.07802 Melbourne Uni Seminar 14/3/2017 Model comparison to pop synth models (with mock observations) § Currently only include small set of isolated binary evolution models (Dominik et al Stevenson+ 2015 2012) – would like to include other channels arXiv:1504.07802 Melbourne Uni Seminar 1/11/2017 17 § Can distinguish between/measure fractions of these two formation Measure mixing channels using the rate and mass fraction with distribution masses Zevin+ 2017 arXiv:1704.07379 M elbourne Uni Seminar 1/11/2017 18 Can also use spins! Melbourne Uni Seminar 1/11/2017 19 § Dynamics Lˆ Spin-orbit (mis)alignment § Isolated binary evolution Lˆ Melbourne Uni Seminar Vitale+ 2015 (1503.04307) 1/11/2017 20 Solid lines are 200 BBH detections, true fraction is colour Melbourne Uni Seminar 1/11/2017 How constraints on model fractions improves 21 with number of observations ¤ Including realistic measurement uncertainties ¤ Drawing increasing number of observations from a multinomial distribution ¤ True fractions shown in blue ¤ Rule out extreme models at > 5σ with ~5 observations Melbourne Uni Seminar Stevenson+ 2017 MNRAS arXiv: 1703.06873 1/11/2017 How constraint on fraction of dynamically formed BBHs 22 evolves with the number of observations Stevenson+ 2017 MNRAS arXiv: 1703.06873 Dark shaded region is 1 sigma, light is 2 sigma Roughly 1/sqrt(nObservations) in the tail Melbourne Uni Seminar 1/11/2017 23 What can we learn from the detections so far? Melbourne Uni Seminar 6/6/2017 24 Dimensionless Spin magnitudes Misalignments Effective spin parameter Mass ratio Melbourne Uni Seminar 1/11/2017 25 Effective spin parameter measurements LVC 2017 arXiv:1706.01812 ) Melbourne Uni Seminar 1/11/2017 26 Our approximation Farr, Stevenson+ 2017 Nature arXiv:1706.01385 Melbourne Uni Seminar 6/6/2017 1/11/2017 27 Spin magnitude distributions Farr, Stevenson+ 2017 Nature arXiv:1706.01385 Melbourne Uni Seminar 1/11/2017 28 Our models Assumes equal masses q=1 Farr, Stevenson+ 2017 Nature Melbourne Uni Seminar arXiv:1706.01385 1/11/2017 29 Our models Assumes equal masses q=1 Farr, Stevenson+ 2017 Nature Melbourne Uni Seminar arXiv:1706.01385 1/11/2017 30 Our models Assumes equal masses q=1 Farr, Stevenson+ 2017 Nature Melbourne Uni Seminar arXiv:1706.01385 6/6/2017 31 Effect of mass ratio Farr, Stevenson+ 2017 Nature Glasgow Seminar arXiv:1706.01385 1/11/2017 32 Results – model comparison L=Low F=Flat H=High I = Isotropic, M=Mixture (see next slide) A=Aligned Farr, Stevenson+ 2017 Nature arXiv:1706.01385 Melbourne Uni Seminar Updated to include GW170814 1/11/2017 33 Mixture fraction Farr, Stevenson+ 2017 Nature arXiv:1706.01385 Melbourne Uni Seminar Updated to include GW170814 1/11/2017 34 Accumulation of significance Updated to include GW170814: Farr, Stevenson+ 2017 Nature arXiv:1706.01385 Melbourne Uni Seminar Updated to include GW170814 1/11/2017 35 Effect of small spins Farr, Stevenson+ 2017 Nature arXiv:1706.01385 Melbourne Uni Seminar Updated to include GW170814 1/11/2017 36 High Flat Low Isotropic Future predictions Aligned Farr, Stevenson+ 2017 Nature arXiv:1706.01385 Melbourne Uni Seminar Updated to include GW170814 1/11/2017 37 Low χeff Low spin Misaligned magnitudes spins Implications: Some wild Dynamic speculation formation? Stripped stars? Supernova? Melbourne Uni Seminar 6/6/2017 Stripped 38 WR stars? ¤ In isolated binary evolution, second black hole forms from a stripped star (WR star) ¤ Binary is either close enough to spin the star up (to maximal) or wide enough to form a black hole with the natal (stellar) spin (since tides are very sensitive to separation) Zaldarriaga + arXiv:1702.00885 See also Glasgow Seminar Hotokezaka and Piran arXiv:1702.03952 1/11/2017 39 § How to link pre-supernova spin of star to remnant spin? § In many cases, need to eject some excess angular momentum. Why not eject it all? § Unlikely since we see high spins in HMXBs (e.g. Miller & Miller arXiv:1408.4145). These are most likely the birth spins Low spin (unaltered by accretion) -> maybe HMXBs are not BBH magnitude from progenitors? § Different formation pathway for BBH than HMXB – supernova? Evolutionary reasons for different spins? § Issue with HMXB measurements? Agreement between Fe line and continuum fitting methods for some systems. § Low spin from SN e.g. Chan et al arXiv:1710.00838 Melbourne Uni Seminar 1/11/2017 40 Low spin magnitude from supernova? Belczynski et al 2017 arXiv:1706.07053 Melbourne Uni Seminar 1/11/2017 Dynamical formation 41 Dynamics ¤ Naturally expect an isotropic distribution of spins (e.g. Rodrgiuez+ 2016 arXiv:1609.05916) ¤ However, predicts too low merger rate to explain all observed events? Rate from Rodriguez+ 2016 arXiv:1602.02444 Melbourne Uni Seminar Figure adapted from arXiv:1606.04856 1/11/2017 42 Black hole natal kicks ¤ BH kicks bounded from above by inferred BBH merger rates ¤ Bounded from below by need for misalignment to explain low effective spins (if BH spins are generally large) Wysocki et al 2017 arXiv: 1709.01943 Melbourne Uni Seminar 1/11/2017 43 2 1 j [cm s− ] 13 14 15 ¤ Spin tilts during supernova as in 5.10 5.10 5.10 3 the Double Pulsar J0737-3039 10 (e.g. Farr+ 2011) 102 101 ¤ Also shown by supernova 100 [Hz] NS modellers (e.g. Kazeroni+ 2017) f 0 100 ¤ No statements in literature for − 101 black hole formation (that I know − R =5 R =3 R =4 R =2 Spin tilts during 2 about) 10 − 101 102 103 f [Hz] supernovae CORE arXiv:1701.07029 + 2017 Kazeroni Melbourne Uni Seminar Farr+ 2011 arXiv:1104.5001 1/11/2017 44 § Gravitational waves measurements of binary black hole masses, spins and merger rates give us insight into their formation § Effective spin for GW150914, GW151226, GW170104, GW170814 and LVT151012 are all clustered around 0 § Either black holes are misaligned with respect to the orbital Conclusions angular momentum, or else they have intrinsically low spins § We showed that given our simple models, the data favour misalignment (provided spins are at least sometimes large) § Misalignment can originate from a linear kick or tilt during a supernova in isolated binaries, and is natural for dynamically formed binary black holes Melbourne Uni Seminar.