neutron star normal modes lsc meeting, baton rouge, march 2004 ligo-g040141-00-z

Neutron Star Normal ModesNeutron Star Normal ModesLSC Meeting, Baton Rouge, March 2004

LIGO-G040141-00-Z

B.S. Sathyaprakash and Bernard Schutz

Cardiff University and AEI

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Neutron Stars

• Great interest in detecting radiation: physics of such stars is poorly understood.

– After 35 years we still don’t know what makes pulsars pulse or glitch.

– Interior properties not understood: equation of state, superfluidity, superconductivity, solid core, source of magnetic field.

– May not even be neutron stars: could be made of strange matter!

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Gravitational Waves from Pulsating Neutron Stars

NS Formation

Dimmelmeier, Font & Mueller (2002)

Secular Instabilities

Andersson, Jones & KK (2002)

NS merger

Shibata & Uryu (2002)

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Stellar Modes

• G-modes or gravity-modes: buoyancy is the main restoring force

• P-modes or pressure-modes: main restoring force is the pressure

• F-mode or fundamental-mode: (surface waves) has an intermediate character of p- and g-mode

• W-modes: pure space-time modes (only in GR, space-time curvature is the restoring agent)

• Inertial modes (r-mode) : main restoring force is the Coriolis force (σ~2Ω/3)

• Superfluid modes: Deviation from chemical equilibrium provides the main restoring agent

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AsteroseismologyNormal mode frequencies and damping times have the same dependence on

R and M

10

4.14

10

34.1 65.1485.22(sec)

1

R

M

R

M

f

Andersson-Kokkotas (1996-98)

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AsteroseismologyUnique estimation of Mass and Radius and EoS

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Signal Strengths of Normal Modes

• Glitch the energy– Crab/Vela glitches could deposit energy in normal

modes as high as 10–12 Msun

• Energy in normal modes when a neutron star forms could be as high as 10–8 Msun

• Normal modes excited due to glitches in Vela will have an amplitude of 10–24

• It is possible that a newly born NS can be observed in normal modes in our own Galaxy

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F- and W- modes in Interferometers

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Analysis Plan

• Make a catalogue of potential sources of normal modes (T. Regimbau)– Glitches in radio pulsars, especially Crab and Vela

• Set up collaborations with Radio, Gamma and X-ray Astronomers to set up time-windows to search for normal modes

– Accretion onto neutron stars could produce seismic disturbances that could lead to intermittent emission of normal modes.

• Should coordinate with X-ray/Gamma-ray observations

• Use existing LAL codes to set up a search pipeline (R. Balasubramanian)– Add a piece to carry out triggered searches for NS modes

– Explore if we can use the existing triggered search codes

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Coordinated Searches with Radio Data

• Why pulsars glitch– 3 decades after pulsars are discovered we don’t fully

understand why pulsars pulse or glitch

– Observing normal modes in neutron stars, combined with radio observations, could teach us about glitches, equation-of-state of high-density neutrons (or other matter)

• Collaborate with Jodrell Bank– Jodrell and can provide glitch data on PSR B0833-45, The

Vela Pulsar and PSR B0531+21, The Crab Pulsar

– Jodrell also has unpublished data on pulsars showing peculiarities in pulse periods – could be looked in coincidence with GW data

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Benefits from the study

• Independent (maybe unique) estimation of stellar parameters (mass, radius, EOS, rotation)

• Understanding of the microphysics in the early stages of NS formation

• Discovering exotic EOS