[PPT] - Neutron Star Merger with Tabulated EOS and Spin Wolfgang Kastaun PowerPoint Presentation

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Neutron Star Merger with Tabulated EOS and Spin

Wolfgang Kastaun MICRA, Stockholm, Aug. 2015

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Topics

Part 1: A recent merger simulation

◮ Gauge independent measures ◮ Structure of post-merger fluid flow ◮ Nature of hot spots ◮ Structure of merger remnant ◮ Matter ejection

Part 2: Influence of initial NS spin on

◮ Inspiral ◮ GW signal ◮ Matter ejection

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Measuring Deformations

◮ Spatial gauge used in evolution bad for analysis of HMNS ◮ Define better coordinates

◮ Consider the equatorial plane ◮ Meaningful coordinate distances

grr = 1, gφφ,φ = 0

◮ Prevent spirals

π

−π

grφ dφ = 0

◮ Fix global rotation

βφ → 0 for r → ∞

◮ Choice of origin: use π-symmetry axis

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Measuring Deformations

◮ Spatial gauge used in evolution bad for analysis of HMNS ◮ Define better coordinates

20 10 10 20 x [km] 20 10 10 20 y [km]

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Measuring Compactness

Problem

◮ Want to quantify density profile and compactness ◮ Compactness should not be sensitive to low density parts ◮ Should not require symmetries or preferred coordinates

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Measuring Compactness

Problem

◮ Want to quantify density profile and compactness ◮ Compactness should not be sensitive to low density parts ◮ Should not require symmetries or preferred coordinates

Solution

◮ Consider shells of constant (rest frame) mass density ◮ Each shell contains proper volume V and baryonic mass Mb

⇒ Unambiguous baryonic mass versus proper volume relations

◮ Compute “volumetric” radius Rv of Euklidian sphere with

same volume

◮ Define compactness C = Mb/Rv ◮ Define the “bulk” as shell with maximum compactness

⇒ bulk mass, bulk volume, bulk entropy..

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Initial data

◮ Irrotational, equal mass ◮ No magnetic field ◮ Zero temperature, β equilibrium ◮ EOS: G. Shen, Horowitz, Teige ◮ Baryonic mass 2 × 1.513 M⊙ ◮ Bulk mass 98% total mass ◮ Grav. mass of single star 1.4 M⊙ ◮ Initial proper separation 57.6 km ⇒ 4 Orbits ◮ Maximum TOV baryonic mass 3.33 M⊙

⇒ Remnant is stable !

◮ Corner case, probably not realistic

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Merger dynamics

Computed isodensity surfaces that contain 1

4 of total mass.

Cut in xy+t:

Inspiral Merger Ringdown

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Merger dynamics

Computed isodensity surfaces that contain 1

4 of total mass.

Cut in xy+t:

Collision: very compact, rapid rotation

1. Bounce

Double core phase Fully merged

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Merger dynamics

Computed isodensity surfaces that contain 1

4 of total mass.

Cut in xy+t:

Angular momentum re-arranges Pattern velocity decouples from fluid velocity

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Merger dynamics

◮ Quantify mass in double core ◮ Total mass of matter with density > central density

5 10 15 20 25 t [ms] 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Mb [M ⊙]

Separate cores Bulk

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GW signal

3 2 1 1 2 3 h at 100 MPc 1e 22

h +

q

h 2

+ +h 2 ×

5 10 15 20 (t−r) [ms] 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 f [kHz]

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GW signal

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 ˜ hf at 100 MPc 1e 24 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 f [khz] 0.0 0.5 1.0 1.5 2.0 2.5 3.0 |h| at 100 MPc 1e 22

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Thermal evolution

◮ Bulk entropy produced at merger, then constant ◮ Matter outside bulk hotter, ongoing heating

5 10 15 20 25 30 t [ms] 1 2 3 4 5 s [kB/Baryon]

Total S/N Bulk Sblk/Nblk Disk Sd/Nd

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