Systematics of prompt black-hole formation in neutron star mergers - - PowerPoint PPT Presentation
Supported by ERC through Starting Grant no. 759253 Systematics of prompt black-hole formation in neutron star mergers Mathematical and Computational Approaches for the Einstein Field Equations with Matter Fields ICERM, virtual, 29/10/2020
with N. Bastian, S. Blacker, D. B. Blaschke, K. Chatziioannou, M. Cierniak, J. A. Clark, T. Fischer, G. Lioutas, T. Soultanis, N. Stergioulas, V. Vijayan
Supported by ERC through Starting Grant no. 759253
► Overview and motjvatjon ► Collapse behavior and simulatjons ► EoS dependence of threshold binary mass
→ constraints on EoS/NS parameters
► Impact of binary mass ratjo ► QCD phase transitjon in NS mergers
→ signature in collapse behavior
► Summary and conclusions
Inspiral of NS binary Neutron star merger Prompt formation of a BH + torus Formation of a differentially rotating massive NS Rigidly rotating (supermassive) NS (stable or long-lived) Delayed collapse to a BH + torus
dependent on EoS, Mtot dependent on EoS, Mtot ~100 Myrs ms ms 10-100 ms
Inspiral of NS binary Neutron star merger Prompt formation of a BH + torus Formation of a differentially rotating massive NS Rigidly rotating (supermassive) NS (stable or long-lived) Delayed collapse to a BH + torus
dependent on EoS, Mtot ~100 Myrs ms ms 10-100 ms
► Collapse movie
Hotokezaka et al. 2011, Bauswein et al. 2013, Bauswein et al 2017, Koeppel et al. 2019, Kiuchi 2019, Agathos et al. 2020, Bernuzzi et al. 2020, Bauswein et al. 2020]
Inspiral Prompt collapse to BH No or delayed collapse to BH
Mthres - EoS dependent (weakly on mass ratjo) !!!
+ strong postmerger GW emission + bright kilonova + …. + +
► Stellar propertjes of NSs uniquely determined by incompletely known high-density
EoS
► Maximum mass (of non-rotatjng!) NSs, i.e. threshold for BH formatjon, not precisely
known (but above ~1.95 Msun)
► In turn, NS observatjons constrain EoS and thus inform about fundamental
constjtuents and interactjons of matuer Some constraints
available e.g. from GW170817 ruling out very large NS radii
Bauswein et al., PRL 2020
► Centrifugal support increases stability: - supermassive – hypermassive NSs ► Uniform rotatjon → about 20% (limited by mass shedding), e.g. Lasota et al. 1996 ► Difgerentjal rotatjon much more (depending on rotatjon law), e.g. Morrison et al. 2004 ► Complex velocity fjeld in merger remnants → a priori maximum mass unclear and has
to be determined by hydrodynamical simulatjons
► Maximum mass in mergers ≡ Mthres in the following Friedman & Stergioulas 2013 Bauswein & Stergioulas 2017 Sequencies of const J e.g. with RNS stellar equilibrium code (Stergioulas & Friedman 1995)
J = 0 Uniform rotatjon
► Binary inspiral: chirp mass and mass ratjo → Mtot typically well measured, q less
accurate
► Merger outcome leaves strong impact on observables:
→ Mthres measurable
► Mthres important to predict outcome and possible search strategies for em
counterparts and postmerger GW and their interpretatjon
► Constraints on Mthres → EoS of high-density matuer (high-density regime) - later
► Mtot accurately measured during inpiral
(from chirp mass and mass ratjo q)
► Combing several detectjons provides Mthres ► Merger product NS vs BH
Direct collapse No direct collapse * determined by highest binary mass with no collapse and lowest mass with direct collapse
► Important questjons:
How does Mthres depend on binary mass ratjo ? How does Mthres depend on EoS ?
► 40 difgerent EoS models (grouped in 3 classes depending on possible assumptjons
about a priori EoS knowledge: w/wo phase transitjon, “excluded” EoSs); most models temperature dependent
► 300-400 simulatjons with relatjvistjc smoothed partjcle hydrodynamics code
(conformal fmatness approximatjon, temperature dependent EoSs – some EoS models with approximate thermal treatment, no initjal spin)
► Calculatjons for difgerent total masses to check outcome for fjxed binary mass ratjo
(q=1 and q=0.7) → Mthres* within at least ± 0.025 Msun * determined by highest binary mass with no collapse and lowest mass with direct collapse
Bauswein et al., PRL 2020
Bauswein et al., PRL 2020
Maximum residual 0.04 Msun, on average 0.02 Msun deviatjon!
Compatjble but betuer than older relatjon
A.B., Baumgarte, Janka, PRL 111 (2013)
Simulation results EoS/TOV properties
arXiv:2010.04461
► Similarly tjght fjts for asymmetric mergers
Other independent variables like Λ(1.4), Rmax, Λ_thretthres
► Bi-linear relatjons → simple to invert ► Similar relatjons for chirp mass
q=M1/M2=1 q=0.7
arXiv:2010.04461
► Either measure X as well and get Y ► Or impose a relatjon between X and Y
measurable Unknown EoS/TOV properties
► From causality or large set of EoSs: ► Measured binary mass and NO collapse:
as arguably for GW170817 with 2.73 Msun
(Margalit & Metzger 2017, Bauswein et. al 2017, Radice et al. 2018, ….)
► For GW170817 we obtain R > 10.6 km ► Applicable to any new observatjon with informatjon on the outcome
→ a lot of potentjal for future – complementary and independent of inspiral fjnite-size efgects
arXiv:2010.04461
(cf. R /Λ limits from Bauswein et al. 2017, Radice et. al 2018, Most et al. 2018, Koeppel et
► Mthres + another NS property (radius or Lambda from other observatjons)
→ very accurate and robust Mmax
see also current estjmates e.g. by Margalit & Metzger 2017, Shibata et al. 2017, Rezzolla et al 2018, Ruiz & Shapiro 2018, Shibata et al. 2019, … (employing GW170817) and Lawrence et al 2015, Fryer et al. 2015, ...
arXiv:2010.04461
Direct collapse No direct collapse
► Instead of R1.6 or Λ1.4 ► Most direct determinatjon via Lambda
bda @ Mthres
es, i.e. combined tjdal deformability of
events which determine Mthres
► Directly measurable with the same events which determine Mthres (with suffjcient SNR) ► Already a single detectjon with informatjon on merger product or poorly constrained
parameters can yield interestjng constraint for prompt collapse
Bauswein et al., PRL 2020
► Instead of R1.6 or Λ1.4 ► Most direct determinatjon via Lambda
bda @ Mthres
es, i.e. combined tjdal deformability of
events which determine Mthres
► Directly measurable with the same events which determine Mthres (with suffjcient SNR) ► Already a single detectjon with informatjon on merger product or poorly constrained
parameters can yield interestjng constraint for prompt collapse excluded
► Mass ratjo may be well measurable for near-by events / but less accurate in more
distant mergers → for both cases we need to understand how Mthres depends on q Farr et al. 2016 GW170817, Abbotu et al 2019 Similar q range for GW190425
@~40 Mpc
► For a selected subset of EoSs determine Mthres(q) ► Typically decrease with binary asymmetry – understandable by Newtonian toy model ► Mthres roughly constant for 0.85 <= q <= 1 ► Higher-order polynomials provide decent descriptjon
→ power of 3 works well for most (tested) EoSs
arXiv:2010.04461
DD2F EoS
► 40 EoS models – consider difgerence
→ Reductjon by asymmetry itself EoS dependent
Bauswein et al., PRL 2020
Mthres for q=1 and q=0.7 Qualitatjve dependence understandble by semi-analytjc Newtonian toy model !!
Only hadronic models
► We found for fjxed q
and for difgerence → suggest to try a combined fjt to the q=1 and q=0.7 data:
► (nearly) as tjght as fjts for fjxed mass ratjo q (average deviatjon 0.017 Msun) ► Useful for applicatjons with a range of q ► Similar relatjons for threshold chirp mass ► Similar relatjons for other R or Lambda (check paper for fjt paramters) ► Valid somewhat below q=0.7
► Impact of EoS on Mthres(q) arXiv:2010.04461
Compatjble with early tentatjve assessments of mass ratjo efgect on stability of remnants, e.g. Bauswein et al. 2013, Bauswein & Stergioulas 2017, Kiuchi et al. 2019, Bernuzzi et al. 2020
(low T, high rho not accessible by experiments or ab-initjo models)
GSI/FAIR
High T, low μ: experiments and lattjce QCD
► Consider additjonal set of hybrid EoSs (with PT to deconfjned quark matuer) in
comparison to purely hadronic EoSs
► Directly measurable from events around Mthres ► Already single events yielding constraints may indicate presence of quark matuer
Measurable from inspiral + information on merger product Measurable from GW inspiral Evidence for quark matter With Mmax > 1.97 !!
Bauswein et al., PRL 2020
► Note: Important that a signature is unambiguously related to a PT, i.e. all possible
hadronic EoS should behave difgerently
► Overplottjng
→ no hadronic EoS can occur in the “hybrid” regime because this would require a lower Mmax, which is excluded by pulsar observatjons → hybrid models can violate this relatjon and occur at relatjvely low Mthres for the given Lambda_thretthres Lambda_thretthres probes moderate densitjes, i.e. hadronic regime, and does not know yet about the sofuening of the EoS at higher densitjes which leads to a “earlier” collapse
arXiv:2010.04461
► Dots show Mthres/2 → phase transitjon occurs afuer merger
Bauswein et al., PRL 2020
► In other words, if there is evidence for a prompt collapse although the tjdal
deformability suggest there shouldn’t → points to a strong phase transitjon
► Already a single measurement may provide interestjng insights ► Also Λ1.4 - Mthres diagram reveals hadron-quark phase transitjon (less clear) Bauswein et al., PRL 2020
► General consideratjon for all EoSs ► General range: 200 < Λthres < 450* (cf. Zappa et al 2018)
→ only for Λthres < 200 we can safely assume a prompt collapse → only for Λthres > 450 / 650 we can safely assume that there was no direct collapse → GW17087: Λ1.37 > 200 (if no direct collapse, i.e. Mthres > 2.73 Msun) (cf. R /Λ limits from Bauswein et al. 2017, Radice et. al 2018, Most et al. 2018, Koeppel et al. 2019, Bauswein et al. 2019, Capano et al. 2020, ...) 200 450* prompt collapse Prompt or no prompt collapse no prompt collapse Λ
Bauswein et al., PRL 2020
► Univariate relatjons between Mthres and high-mass NS propertjes (R and Lambda) ► Insensitjve to presence of phase transitjon arXiv:2010.04461
► Characteristjc increase of postmerger frequency compared to tjdal deformability
→ evidence of presence of quark matuer core → in any case constraint on onset density of hadron-quark phase transitjon
A.B. et al, PRL 2019
from the inspiral from postmerger
with strong 1st order PT
Green models with phase transitjon to quark matuer [Fischer et al. 2018]
► Outcome one of the most basic characteristjcs of a merger – quantjfjed by Mthres ► Tight relatjons describing Mthres as functjon of stellar parameters (for fjxed q) ► Allows constraints on these parameters, e.g. Mmax
→ probed the very high density regime of EoS (which may be hard to access otherwise) → interestjng radius constraints from current and future multj-messenger observatjons
► Binary mass asymmetry typically leads to lower Mthres (less stability) – in systematjc
dependencies
► Generalized tjght (!) fjt formulae for Mthres with explicit q dependence ► Phase transitjon to deconfjned quark matuer can lead to reductjon of Mthres
→ unambiguous signature in Mthres-Lambda_thretthres plane → importance of instruments and search strategies for follow-up in GW and em