Compact%20Stars%20as%20Sources%20of%20Gravitational%20Waves

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Compact Stars as Sources of Gravitational Waves

• Y. Kojima (Hiroshima Univ.)

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?3?TAMA???????(?)2003?2?6-7?
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Available Energy Sources

• Rotational Energy
• ( Instabilities)
• -gt Continuous GW
• Binding Energy(Externally driven
  deformation)(Formation /Phase transition)
• -gt Burst-like GW
• (cf. Elastic Energy in Crust)

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Brief Review of R-Mode Instability

• Unstable for all rotating stars
• Importance of coupling
• evolution of amplitude

unstable growth
mode coupling
Non-linear Saturation
Magnetic field Rezzolla et al (1999)
Hydrodynamical Cascade Gressman et
al(2002),Arras et al (2002)
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Decaying R-mode Scenario?
Gressman et al(2002) Cascade decay of
unstable mode
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Implications

• Various (unknown) instabilities on rotating stars
• -gt Non-axially symmetric deformation
• -gt Gravitational radiation
• Weakly growing mode has a small amplitude
• -gt Less important for first detection
• Sources for 2nd generation detector

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A New Type of Compact Stars?

• RX J185635-3754 nearby NS? D100pc
• 1996 Discovered at X-ray/Optical
• 2002 Drake et al(ApJ.572, 996)
• radiation radius3.8-8.2 km -gt Quark
  star?
• Not yet confirmed
• 2002 Walter Lattimer (ApJ.576,L145)
• 15 (D/117pc)km Two-components blackbody
• 2002 Burwitz et al (astro/ph0211536)
• 12(D/120pc)km

Neutron star
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Whats a quark star?

• Bare quark star
• Bodmer-Wittens Conjecture
• Strange matter (u,d, s-quarks) is the ground
  state
• simple description (MIT bag model
• B is bag constant)
• (cf.) Hybrid quark star (quark core)

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Neutron Stars vs. Quark Stars

• Static properties
• (mass M, radius R)
• -gtCompact!
• -gt Strange star as rapidly rotating pulsar with
  P0.5ms

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Mass and Radius of Compact Star
gravitationally bound star
Lattimer Prakash(2001)
self-bound star
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Dynamical Property of a Star- Characteristic
Frequency -

• Wave form of damped sine curve
• (frequency and damping time)
• e.g. Black hole ringing
• (Chandrasekhar Detweiler)
• Neutron stars
• (Lindblom Detweiler)
• However, excitation is unclear.

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Complex Frequency
Kojima Sakata(2002)
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Frequency and Damping Time
Kojima Sakata(2002)
average density
relativistic factor
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Results

• Two parameters from
• frequency( average density) and
• damping time (relativistic factor)
• -gt M, R are inferred.
• Important information for EOS
• Discriminating quark star from neutron star

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Optimistic Estimate

• Marranghello et al (2002)
• Phase transitions in neutron stars and GW
  emission
• Typical binding energy

Matched Filter S/N 2
Fraction of energy to non-radial oscillation is
not clear.
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Summary

• Simple system (BH/NS binary) for
• 1st detection
• Complicated system as future targets
• should be studied
• theoretically (or experimentally).