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

March 10, 2004 2Neutron Star Normal Modes Sathyaprakash and Schutz

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!

March 10, 2004 3Neutron Star Normal Modes Sathyaprakash and Schutz

Gravitational Waves from Pulsating Neutron Stars

NS Formation

Dimmelmeier, Font & Mueller (2002)

Secular Instabilities

Andersson, Jones & KK (2002)

NS merger

Shibata & Uryu (2002)

March 10, 2004 4Neutron Star Normal Modes Sathyaprakash and Schutz

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

March 10, 2004 5Neutron Star Normal Modes Sathyaprakash and Schutz

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)

March 10, 2004 6Neutron Star Normal Modes Sathyaprakash and Schutz

AsteroseismologyUnique estimation of Mass and Radius and EoS

March 10, 2004 7Neutron Star Normal Modes Sathyaprakash and Schutz

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

March 10, 2004 8Neutron Star Normal Modes Sathyaprakash and Schutz

F- and W- modes in Interferometers

March 10, 2004 9Neutron Star Normal Modes Sathyaprakash and Schutz

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

March 10, 2004 10Neutron Star Normal Modes Sathyaprakash and Schutz

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

March 10, 2004 11Neutron Star Normal Modes Sathyaprakash and Schutz

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