Precessing BH NS Binaries: Upper Limits on Black Hole Spins Richard O’Shaughnessy
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Transcript Precessing BH NS Binaries: Upper Limits on Black Hole Spins Richard O’Shaughnessy
Precessing BH NS Binaries:
Upper Limits on Black Hole Spins
Jeff Kaplan
Richard O’Shaughnessy
Vicky Kalogera
Department of Physics and Astronomy
Motivation
Precession:
Important for BH NS
systems
GW signal dependant on
BH spin and tilts
Spin tilts result from
companion SN
Effect of Precession
Spin tilts for
BH-NS systems:
Already studied
(Apostolatos et al; Grandclement et al;
Buonanno et al)
o
Critical for > 30
Fitting Factor: Function of Tilt
Spin Magnitudes for
BH-NS systems:
???
Rate Reduction:
Function of Magnitude
Spin Magnitudes From
Population Synthesis
StarTrack code for BH – NS formation
(Belczynski et al. 2004)
Stable & unstable mass transfer
Stellar winds
Supernovae & natal kicks
GR & tidal evolution
Isolate populations of coalescing BH-NS
systems for wide range of StarTrack models
Examine spin evolution and mass transfer
history of BH
How do Black Holes get spun up?
Core collapse processes not well understood
Birth spins?
Estimate from observed NS spins
Birth NS spins: 10-20 ms.
Birth NS a: 0.019 - 0.038
Assumption: Initial BH spins negligible.
Accretion Spin up
Thin Disk
Common Envelope (CE)
Assume angular momentum at
innermost orbit accreted
onto BH (Bardeen 1974)
Dynamically unstable
mass transfer that leads
to spiral in and envelope
mass ejection
Results on Mass Transfer
Thin disk Accretion
log10(Δm/m)
F(Δm/m)
Common Envelope Accretion
Δm/m
96%: a < 0.01
Minimal spin-up due to thin-disk accretion
Most of mass is accreted in CE phase!
Common Envelope Accretion
Bad: CE accretion not well understood
Complex 3-D accretion
Non-adiabatic hydrodynamical process
Hypercritical accretion reaches
highly Super-Eddington rates
Good: Assuming disk accretion – Upper Limit
Why?
– Disks carry large angular momentum
Common Envelope Spin Up Results
Two possibilities
BH enters CE phase:
BH
Accretion Induced Collapse (AIC): NS
BH
BH
Observations show NS spin up in CE inefficient
Known Recycled Pulsar Spins that are
thought to have been spun up in CEs:
B1913+16:
B1534+12:
J0737-3039:
CE
a = 0.0033
a = 0.0057
a = 0.0096
In AIC cases, expect BH birth spin to be very small
Common Envelope Spin Up Results
F(a) from Common Envelope Accretion
Probability per 0.1 spin
BH spin - a
This is an Upper Limit! Thin disk model assumed
Precessing BH-NS and GW searches
Astrophysical average <FF3> if
non-precessing templates are
used:
Plot Thanks to Mia Ihm
Precessing BH-NS and GW searches
Astrophysical average <FF3> if
non-precessing templates are
used:
Effect of Spin Magnitude
on GW signal:
∫ f(a) • FF3(a) da = <FF3>
Plot Thanks to Mia Ihm
<FF3> = 0.84
Conclusions and Future Work
BH-NS Binaries:
Negligible BH accretion and spin-up in thin-disk phases
Significant BH accretion in CE phases
Upper limit on average reduction of BH-NS in-spiral
event rate: 0.84
Future Work
Explore CE physical conditions and reduce upper limits on
BH spin-up
Better constrain BH birth spin using population models and
observed systems