Learning about Black- Hole Forma5on by Observing Gravita5onal Waves. Michael Kesden (UT Dallas) PPC 2017 Mee5ng Corpus Chris5, TX May 22, 2017

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1 Learning about Black- Hole Forma5on by Observing Gravita5onal Waves Michael Kesden (UT Dallas) PPC 2017 Mee5ng Corpus Chris5, TX May 22, 2017

2 Outline What are gravita5onal waves (GWs) and how do observatories like the Laser Interferometer Gravita5onal- wave Observatory (LIGO) detect them? How do binary black holes (BBHs) form in our Universe? Cluster channel BHs form first, binaries later Field channel Binaries form first, BHs later What BH masses and spins are predicted by these astrophysical forma5on channels? How do these spins evolve between BBH forma5on and merger? Can LIGO dis5nguish the forma5on channels?

3 What are gravita5onal waves? Electromagne5c Gravita5onal Electromagne5c fields E, B Metric perturba5ons h μν = g μν η μν Solu5ons to ( 2 / 2 t 2 )X = 0 same Propagate at speed of light same 2 transverse polariza5ons same Sourced by 5me- varying charges Sourced by 5me- varying stress- energy

4 Observing gravita5onal waves BBHs emit GWs that cause incomplete destruc5ve interference between lasers in arms of LIGO interferometer. Supermassive BBHs are GW source for PTAs, LISA.

5 GW The Event Two BBH mergers (also GW151226) in 4 months of O1 data. Many more expected in O2 and beyond as Virgo, KAGRA, LIGO- India added to network later this decade. Two key goals of LIGO: test GR and discover origin of these BBHs.

6 Tes5ng GR with GW Upper bounds on discrepancies between measured post- Newtonian (PN) coefficients and GR predic5ons. LIGO es5mates the mass M f and spin a f of final BH produced in merger self consistently in all 3 stages. GR allows any value for M f and 0 a f 1; what determines the BH masses and spins LIGO actually sees?

7 Origin of stellar- mass black holes Stars are powered by nuclear fusion fusion ends when most stable element (Fe) is produced. Fe core above 1.4 M cannot be supported by electron degeneracy pressure core collapse triggers supernova. Nuclear pressure cannot support cores above 2 M these cores collapse to BHs. BHs can accrete from stellar companions, we see X- rays emihed by accre5on disk. Cygnus X- 1 discovered in 1964.

8 Cluster channel BHs form first Energy equipar55on between stars in cluster heavy BHs sink to center BHs form 5ght binaries through 3- and 4- body processes (Rodriguez+ 2016) BBHs ejected from cluster and later merge through GW emission Predicts heavy masses, isotropic spins

9 Field channel binary forms first Begin with massive main- sequence binary (Gerosa, Kesden+ 2013) Primary transfers envelope to secondary, mass- ra5o reversal? Primary core collapse, asymmetric explosion 5lts orbital plane Common- envelope evolu5on, 5dal alignment of secondary? 2 nd core collapse, 2 nd orbital 5lt, primary spin more misaligned GW- driven inspiral from r 10 7 r g into LIGO band, must evolve spins

10 Post- Newtonian spin precession EOM can be expanded about Newtonian solu5on when: v c, r r g = GM/c 2 Very good approxima5on for astrophysics: r g /r 10-6 (M/10 M )(r/10 R ) mescales for BBH evolu5on Orbital 5me t orb (r 3 /GM) 1/2 Precession 5me t pre (t orb /η)(r/r g ) t orb Radia5on- reac5on 5me t RR (t orb /η)(r/r g ) 5/2 t pre Solved BBH spin precession analy5cally at 2PN (Kesden+ 2015)

11 BBH Precession Anima5on

12 Spin morphology Keplerian orbital shape determined by a, e Spin- precession morphology determined by L, J, ξ

13 BBHs in LIGO band remember their birth! Cluster forma5on isotropic spins uniform distribu5on Field forma5on spins aligned top right corner θ 1 θ 2 if 5des realign secondary spin between SNs θ 1 > θ 2 if primary evolves to more massive BH (red region) θ 1 < θ 2 if secondary evolves to more massive BH due to mass ra5o reversal before first SN (blue region) Final spin morphologies set by iniial spin direc5ons

14 Bayesian astrophysical model selec5on Iden5fy frac5on f a of aligned spins with ~100 BBH detec5ons, possible by end of O3 observing run (Vitale+ 2017). Es5mate contribu5ons λ i from 4 forma5on models (Stevenson+ 2017)

15 LIGO can measure spin morphologies! Spin precession modulates GWs; more modula5on for ΔΦ 0 morphology because spin components to L add construc5vely. LIGO can measure total angular momentum J and projected effec5ve spin ξ, correctly iden5fy morphology (Trifirò, Kesden+ 2016).

16 Conclusions LIGO observed GWs from two BBH mergers. BBH spins are misaligned with the orbital angular momentum, modula5ng the GWs they emit. Stellar evolu5on of BBH progenitors determines spin misalignments at BBH forma5on: Cluster channel BHs form first isotropic spins Field channel binaries form first spins partly aligned with orbital angular momentum, morphology set by mass ra5o reversals, 5dal alignment LIGO can measure spin direc5ons, morphologies, unlocking origins of astrophysical BH forma5on.