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Supercritical Accretion in the Evolution ofNeutron Star Binaries and Its Implications

QCS2014@2014.10.20Chang-Hwan Lee @1Nuclear Physics A 928 (2014) 296()1

Prakash (2013)All well measured NS masses in NS-NS binaries are < 1.5 Msun21.97 & 2.01 Msun NS were observed in NS-WD binariesWhy all well-measured NS masses in NS-NS binaries are less than 1.5 Msun?

NS mass may/should depend on the evolution processHigh-mass neutron stars in NS-White Dwarf binaries1.97 solar mass NS : Nature 467 (2010) 10812.01 solar mass NS : Science 340 (2013) 6131Our open questions34ContentsPart I : What we discovered in BH binaries

Part II : What if we apply the same evolution process to neutron star binaries ?5Part I. What we discovered in BH binaries

ApJ 575, 996 (2002)Black Hole Binaries (Soft X-ray Transients)

MBH (Msun)Orbital period (days)Main Sequence companion Evolved companion6Q3) Evolution of Donor StarQ1) Evolution of BH/NS ProgenitorCurrent ObservationProgenitorsQ2) What happens at birth ?7 Q) How can we understand the population of SXTs ?Tidal interaction just before BH formationrapidlyspinning BHFeSynchronization of BH-Progenitor Spin & Binary Orbital Period8

Reconstructed BH Binaries at Birth9

Pre-explosion orbital period (days) Rapidly spinning black holes at birth10ApJ 575, 996 (2002)

Pre-explosion orbital period (days) Rapidly spinning black holes at birth4U 1543-47GRO J1655-40Shafee et al. (2006)1112

Kerr parameters & Energies involvedApJ 727:29 (2011)13What if we apply the same evolution process to neutron star binaries ?Supercritical accretion in NS binariesPossibilities of `NS + high-mass NS/BH` binariesPart IIEddington Luminosity & Eddington Limit

14Supercritical Accretion onto first-born NSEddington Accretion Rate : photon pressure balances the gravitation attractionIf this limit holds, neutron star cannot be formed from the beginning (e.g. SN1987A; 108 Eddington Limit).Neutrinos can take the pressure out of the system allowing the supercritical accretion when accretion rateis bigger than 104 Eddington limit ! (T > 1 MeV : Thermal neutrinos dominates !)Q) What is the implications of supercritical accretion, if it works ?15

Giant StarOne has to understand formation of BH/NSBH or NS16

Fe core mass before collapse (Brown et al. New Aston. 6,457)Neutron StarOpen Box & Circles: in close BinariesJ1614-2230?1718

In 2007we discussed that NS masses in NS-NS binaries may be the result of evolution, not an indication of maximum NS mass.We discussed the possibility that the maximum mass of NS can be significantly higher than 1.5 solar mass.ApJ 670:741 (2007)Fresh NS mass from Fe core collapseIn close binaries (evolution without H envelope)low Fe core mass NS mass = 1.3 - 1.5 MsunThis value is independent of NS equation of state.Q) What is the fate of primary (first-born) NS in binaries ?19 Final fate of first-born NS

Evolution of Companion1st-born NSNS + accretionHeAccretionFe2nd NS/WD20

NSNSABLife timeHeHHHeCase 1 ABNo accretion : nearly equal mass NS-NS binary!21

H red giantHe red giantNSNSABLife timeHe+0.2 Msun First born NS should accrete only < 0.2 M !HCase 2AB22

H red giantHe red giantWDNS90%10%ABLife timeH He He+0.7 Msun +0.2 Msun Supercritical Accretion: First born NS can accrete up to 0.9 M !Case 3AB2324Possibilities of `typical NS` + `high-mass NS/BH` binariesHow mass & orbit change during the evolution? A few efficiencies (not calculable from first principles)

25cd=6, ce=0.2are consistent with SXT(Soft X-ray Transient)Lee,Brown,Wijers,ApJ(2002)Belczynski et al., ApJ, 572, 40726

Final mass of first-born NS with supercritical accretion observedobserved

Can we see BH-NS binaries as pulsars even if they exist ?Pulsar life time : 1/BFresh pulsar : B1012 G NS-NS if first-born NS is recycled by accretion longer pulsar life time (B108 G) larger beaming angle bigger chances to be observed BH-NS no recycled pulsar much smaller chances to be observed 27GW sources with NSNS-NS already seenNS-BH/HMNS no evidence yet can contribute to GW if exist28Consequences of supercritical accretion, if it worksdifferent class of NS binaries may exist`high mass NS/BH ( > 2 solar mass)` + `typical NS`could be hidden GW sources

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Nature 514, 202 (9 Oct. 2014)Courtesy of Hao TongMany Thanks

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Pre-explosion orbital period (days)Uncertainties [4U 1543-47]4U 1543-47Shafee et al. (2006)32arXiv:1408.7028PcurrentPreconstructed

33Evolution after BH formation

GRS 1915+105Low-spin black holes at birth34Spin-up due to conservative accretion

McClintock et al. (2006) Pre-explosion orbital period (days)GRS 1915+105a* > 0.9835