double compact objects: detection expectations vicky kalogera physics & astronomy dept...
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Double Compact Objects: Double Compact Objects: Detection ExpectationsDetection Expectations
Vicky KalogeraPhysics & Astronomy DeptNorthwestern University
with
Chunglee Kim (NU)Duncan Lorimer (Manchester)Philippe Grandclement (NU)
Mia Ihm (NU)
In this talkIn this talk : :
• Gravitational Waves, Gravitational Waves,
Ground Based Interferometers and Ground Based Interferometers and
Astrophysical SourcesAstrophysical Sources
• Double Compact ObjectsDouble Compact Objects
NS-NS, BH-NS, BH-BHNS-NS, BH-NS, BH-BH o Event RatesEvent Rates : : newly discovered NS-NS !newly discovered NS-NS !
o Physical PropertiesPhysical Properties : : what will we learn ?what will we learn ?o Data AnalysisData Analysis : : challenges … challenges …
The strongest sources of gravitational waves are massive compact objects moving at relativistic speeds
GW amplitude: GW amplitude: h ~h ~
Still their effect is very weak :10 M10 M
oo BH at the Galactic center: BH at the Galactic center: h ~ 10 h ~ 10 -17-17
10 M10 Moo BH at the Virgo cluster: BH at the Virgo cluster: h ~ 10 h ~ 10 -20-20
1r
GM
c2
äc
2
h ~ 10 -20
L ~ 4 km l ~ 0.01 fm
LIGO :
'
~~ '
IFO Noise Level and Astrophysical Sources
Seismic at low freq. Thermal at intermediate freq. Laser shot noise at high freq.
Double Compact Objects Inspiral and Coalescence
Compact Object FormationCore collapse-Supernovae
Spinning Compact Objects Asymmetries-Instabilities
Early UniverseFluctuations-Phase Transitions
Binary Compact Object Inspiral
Do they exist ? YES!Prototype NS -NS: binary radio pulsar PSR B1913+16
What kind of signal ?
inspiral chirp
GW emission causes orbital shrinkage leading to higher GW frequency and amplitude
orbitaldecay
PSR B1913+16
Weisberg &Taylor 03
Sensitivity to coalescing binaries
What is the expecteddetection rate out to
Dmax ? Scaling up from
the Galactic rate
strength ~ 1/r
detection rate ~ r3
Dmax for each signal sets limits on the possible detection rate
Inspiral Rates for the Milky Way
Theoretical Estimates
Based on models of binary evolution until binary compact objects form.
for NS -NS, BH -NS, and BH -BH
Empirical Estimates
Based on radio pulsar evolution and survey selection effects.
for NS -NS only
Population synthesis models: follow evolution of primordial binaries until
double compact objects form involve: physical properties of primordial binaries mass exchange between binary components mass and angular momentum loss from binary asymmetric core collapse events
Theoretical Rate Estimates
Large number of possible evolutionary phases result in a large number of formation channels with different relative efficiencies and different physical properties for double compact objects
Rate predictions: sensitive to model assumptions estimates are uncertain by 3-4 orders of magnitude !
Detected NS -NS binaries: binary pulsars
One of the two NS One of the two NS emits radio pulsesemits radio pulses
Prototype NS -NS: Prototype NS -NS: Hulse -Taylor pulsarHulse -Taylor pulsarPSR B1913+16PSR B1913+16
Also: Also: B1534+12 and B1534+12 and J0737-3039 J0737-3039 (Burgay et al. 2003)(Burgay et al. 2003)
pulsar as a`lighthouse'
Radio pulsar surveys have strong selection effects and most of the pulsars remain undetected
QuickTime™ and aGIF decompressorare needed to see this picture.
Radio Pulsarsin
NS-NS binaries
NS-NSMerger
Rate Estimates
Use of observed sample and models for PSR survey selection effects: estimates of total NS- NS number combined with lifetime estimates
(Narayan et al. '91; Phinney '91)
Dominant sources of rate estimate uncertainties identified: (VK, Narayan, Spergel, Taylor
'01)
small - number observed sample (2 NS - NS in Galactic field)
PSR population dominated by faint objects
Robust lower limit for the MW: 10-6 per yr
Upward correction factor for faint PSRs: ~ 1 - 500
X3
small-N sample is: > assumed to be representative of the Galactic population > dominated by bright pulsars, detectable to large distances total pulsar number is underestimated
pulsar luminosity function:
~ L-2
i.e., dominated by faint, hard-to-detect pulsars
NG
Nest
median
25%
(VK, Narayan, Spergel, Taylor '01)
Radio Pulsarsin
NS-NS binaries
NS-NSMerger
Rate Estimates
(Kim, VK, Lorimer '02)
It is possible to assign statistical significance
to NS-NS rate estimates with Monte Carlo simulationsBayesian analysis used to derive the
probability density of NS-NS inspiral rate
Probability Distribution of NS-NS Inspiral Rate
Choose PSR space & luminosity distribution
power-law constrained from radio pulsar obs.
Populate Galaxy with Ntot ‘‘1913+16-like’’ pulsars
same pulsar period,
pulse profile,
orbital period
Simulate PSR survey detection and produce lots of
observed samples for a given Ntot
Distribution of Nobs for a given Ntot : it is Poisson
Calculate P ( 1; Ntot )
Use Bayes’ theorem to calculate P(Ntot) --> P(Ntot x fb
Ntot x fb = rate
Repeat for each of the other two known NS-NS binaries
Current Rate Predictions
3 NS-NS : a factor of 6-7 rate increase
Initial LIGO Adv. LIGO per 1000 yr per yr
ref: peak 75 400
95% 15 - 275 80 - 1500
opt:peak 200 1000
95% 35 - 700 200 - 3700
Burgay et al. 2003VK et al. 2003(Nature embargo)
Current expectations for LIGO II (LIGO I)detection rates of inspiral events
NS -NS BH -NS BH -BHDmax 350 700 1500 (Mpc) (20) (40) (100)
Rdet 5 - 3700 1.5 -1500 15 -10,000(1/yr) (10-3 - 0.7) (3x10-4 -0.3) (4x10-3 -3) less reliable (pop - syn)
Use empirical NS-NS rates:Use empirical NS-NS rates:constrain constrain pop syn models > BH inspiral ratespop syn models > BH inspiral rates
Q: What will the detection of compact object inspiral events tell us ?
discovery of the first BH -NS or BH -BH binaries
compact object mass measurements relative ratios of binary types
more constraints on pop syn models and more constraints on pop syn models and binary evolution binary evolution
distance measurements localization (~ few degrees)
spatial distribution association with EM sources
Gravitational-Wave Astronomy
Challenges in the near future...
Technical: achieve target noise level
Data analysis: optimal methods for signal retrieval detection of inspiral signal requires: template waveforms and matched filtering techniques
Precession and Inspiral Waveforms
Compact object binaries can precess if spins are of significant magnitude and misaligned with
respect to the orbital angular momentum.
Precession can modify inspiral waveforms and decrease the detection efficiency of matched
filtering techniques.
Precession effects are more important for binaries of high mass ratios (BH-NS) and with spin tilt angles
of the massive object in excess of ~30°.(Apostolatos 95)
Q: What is the origin of spin tilt angles in compact object binaries ?
Mass transfer episodes in binaries tend to align spin and orbital angular momentum vectors.
However, asymmetric supernova explosions can tilt the orbital plane relative to the spin of the non-exploding star.
BH
BHNS
SN + NS kick SN + NS kick
Q: What are the expected spin tilt angles ?
10 Mo BH
1.4 Mo NS
Ignoring precession effects in the templatescan decrease the detection rate by a
significant factor
VK 2000
with non-precessing templates: detection rate decreasesR
det decrease depends on
spin magnitude and tilt angle:
Grandclement, VK, Vecchio 2002Grandclement & VK 2003Grandclement, Ihm, VK, Belczynski 2003see also Buonanno et al. 2003 Pan et al. 2003
cos(spin tilt angle)
Maximum BH spin
cos(spin tilt angle)
For a 10-1.4 Mo BH-NS binary
templates that can mimicthe precession effects can increase the detection rate:
Precessing inspiral binariesPrecessing inspiral binaries
3
(BH spin)
10 Mo BH
1.4 Mo NS
Rate drop expected Rate drop expected from from astrophysical predictionsastrophysical predictions for spin tilts in BH-NS binariesfor spin tilts in BH-NS binaries
Grandclement, Ihm, VK, Belczynski 2003
rate dropby 40%
In the near and distant future ... Initial LIGO 3 NS-NS ---> detection possible
BH-BH ---> possible detection too
Advanced LIGO expected to detect compact object inspiral as well as NS or BH birth events, pulsars, stochastic background past experience from EM: there will be surprises!
Laser Interferometry in space: LISA sources at lower frequencies supermassive black holes and background of wide binaries