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Compact Binaries Cole Miller, University of Maryland

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Compact Binaries. Cole Miller, University of Maryland. Outline. Overview of amplitudes and frequencies Neutron stars and black holes Benefits of detection at ~1 Hz The most massive white dwarfs Long lead times for telescopes Nonzero eccentricities? - PowerPoint PPT Presentation

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Page 1: Compact Binaries

Compact BinariesCole Miller, University of Maryland

Page 2: Compact Binaries

Outline

• Overview of amplitudes and frequencies

• Neutron stars and black holes

• Benefits of detection at ~1 Hz The most massive white dwarfs Long lead times for telescopes Nonzero eccentricities?

• Intermediate-mass black holes

Page 3: Compact Binaries

Amplitude of Gravitational Waves

Binary of reduced mass , total mass M.At luminosity distance d, frequency fGW,dimensionless strain amplitude is h=2x10-22 (fGW/10Hz)2/3(Mch/10 Msun)5/3(100Mpc/d)

where Mch5/3=M2/3 defines the “chirp mass”.

Page 4: Compact Binaries

Frequency of WavesThe frequency at the innermost stablecircular orbit (ISCO) for a nonrotating hole is fGW(ISCO)=4.4x103 Hz (Msun/M)For rotating, up to fGW(ISCO)~2x104 Hz (Msun/M)

More generally, object of average density has maximum frequency ~(G)1/2

Neutron star: ~2000 Hz White dwarf: up to ~1 Hz

Page 5: Compact Binaries

NS-NS Binary Formation• Observation of NS-NS

binaries calibrates models Big model uncertainties!

• Rate dominated by field binaries, not binaries in globular clusters

• Best estimate: 10-6-10-4

yr-1 MWEG-1

• Detection rates: 10s per year for next generation

http://www.astro.lu.se/Research/OTA/compactBinaryFormation.jpg

Page 6: Compact Binaries

Benefits of NS-NS/NS-BH• 10s/yr NS mass determinations, especially

accurate for asymmetric systems such as BH-NS• Radius measurements from phase; if dR/R<0.1,

goes a long way towards resolving EOS

Shibata et al. 2009

Need h<10-22

at 1-3 kHz

MBH/MNS=3Nonrotating BHDifferent NScompactnesses

Page 7: Compact Binaries

Stellar-mass BH binaries: Born• None observed (how

could they be!) Rates unclear

• Rely on theory Uncertain common envelope, kicks, etc.

• Masses, mass ratios, spins not well constrained

• AdLIGO: 10s/yr???

Page 8: Compact Binaries

Stellar-mass BH Binaries: Made

• In dense stellar env, can swap into MS bin

• Biases towards high-mass objects

• Rates depend on retention in system Easy escape from GC Tougher from nucleus

C. Miller

Page 9: Compact Binaries

Stellar-mass BH Binaries 3: Nuclear Star Clusters

• Common in centers of small galaxies Follow M- relation

• Escape speeds 150-250 km/s

• BH retained after SN• Almost all binaries

stay in center after 3-body interactions GW recoil can eject

Miller & Lauburg 2009

Page 10: Compact Binaries

Stellar-mass BH Binaries 3: Nuclear Star Clusters

• AdLIGO estimate: Tens to >100 per year

• Strong bias towards massive binaries Heavy things exchange

• Low frequencies mean num rel is especially important

Advanced LIGO noise curveGrav. physics group, Cardiff

fISCO=4400Hz/[Mtot(1+z)] =100 Hz if Mtot=30, z=0.5

Page 11: Compact Binaries

Spin Measurements

• Fe K line profile fits (Tanaka et al. 1995)

• Continuum energy spectral fits

• QPO modeling

How can we measure spins?

My candidate for most reliable is theline profile fits, but all have largesystematic issues (known unknownsand unknown unknowns!)Best estimates of spin vary, from~0.7 to >0.98 depending on source

Page 12: Compact Binaries

The Most Massive WD• ~108-9 WD binaries in Milky Way

• Even small fraction with M~1.4 Msun gives large number; new category of sources

http://cococubed.asu.edu/images/coldwd/mass_radius_web.jpg

fGW=1 Hz

Page 13: Compact Binaries

Advance Warning of Merger

• EM counterparts to mergers: lots of info! Precise localization Nature of transients

• Time to merger scales as finit

-8/3

• At 1 Hz, could be identified days in advance

• Key: how soon could GW be localized? Rotation of Earth? 1.4 Msun - 1.4 Msun binary

Page 14: Compact Binaries

Nonzero Eccentricities?

• Usually, think of binary GW as circular ~true for >10 Hz or field binaries

• Dynamical interactions can change, e.g., Kozai in dense systems

• e~1/f for e<<1• Low freq important for

inferring dynamic origin Miller & Hamilton 2002L. Wen 2003

Page 15: Compact Binaries

Intermediate-Mass Black Holes

Mass between 102 and 104 Msun

Too massive to have formed from solitary star in current universe, butsmaller than standard supermassiveblack holes.

Page 16: Compact Binaries

Context and Connections

• In z~5-30 universe, seeds for SMBH

• In local universe, probes of star cluster dynamics

• Potentially unique sources of gravitational waves (ground and space)

Wechsler et al. 2002

Page 17: Compact Binaries

Formation of IMBHs

• Problem: ~103 Msun too much for normal star!

• Population III stars Low Z; weak winds

• Collisions or mergers Needs dense clusters Young: collisions Old: three-body

Gurkan et al. 2006

Portegies Zwart & McMillan

>1 IMBH in single cluster?

Page 18: Compact Binaries

IMBH-IMBH Visibility• ~few x 1000 Msun binary visible to z>5.

• Reasonable rates: few tens per year at >1 Hz• Unique probe of dense cluster star formation

Fregeau et al. 2006

Page 19: Compact Binaries

Conclusions• Binaries are the only guaranteed

gravitational wave sources• Detection of NS-NS or NS-BH will lead to

great advances in knowledge of EOS• Nuclear star clusters are promising factories

for compact binaries• Many benefits of low frequency, including:

Possible detection of white dwarfs Long lead time for EM observations Intermediate-mass black holes

Page 20: Compact Binaries

What Can Massive WD Do For You?

• Precise maximum mass depends on composition, other properties

• Massive WD (in binaries with normal stars) thought to be Type Ia SNe progen.

• Mergers would be spectacular but short-lived EM events How much lead time do we have?

Page 21: Compact Binaries

Why Are We Not Sure?

• Stellar-mass (5-20 Msun) and supermassive (106-1010 Msun) BH are established with certainty

• Why not IMBH (102-104 Msun)?

• Lack of dynamical evidence Too rare for easy binary observations Too light for easy radius of influence obs

• Attempts being made, but settle for indirect observations in the meantime

Page 22: Compact Binaries

Low-Mass SMBH?

Greene and Ho 2006

Masses below~106 Msun areinferred indirectly,but extrapolationsuggests M~104 Msun

for numerous smallgalaxies

Central massiveblack holes

Page 23: Compact Binaries

Stellar-Mass BH Spin

• Is spin changed much by accretion? King & Kolb 1999

• Not a lot, if prograde Little mass accreted

• Current spin parameter is ~good representation of spin at birth

• Direction not so clear!

Page 24: Compact Binaries

Observing GW from IMBH

• Stellar-mass BH with IMBH? Promising at >1 Hz (Mandel et al. 2008)

• IMBH with IMBH Plausible with low freq; occur if binary fraction >10% (Fregeau et al. 2006)