Neutron Stars GlitchesEmilie Parent

EPSC 510 Presentation

November 10th

Outline

1. What is a neutron star2. Observations of neutron stars3. Interior of neutron stars4. Glitches

1. What is a neutron star

1. What is a neutron star

Forms when a massive star dies in a supernova explosion

1. What is a neutron starSupernova remnants seen by NASA’s telescopes

1. What is a neutron starSupernova remnants seen by NASA’s telescopes

Enormous amount of energy released The core collapses Neutron star is born

Energy stored in angular momentum

1. What is a neutron star

A neutron star is ..

VERY hotVERY denseVERY magnetized VERY stable rotationally

..and VERY cool

2. Observations of Neutron Stars

2. Observations of Neutron Stars

A Pulsar is ..

A rotating neutron star emitting beams of radiation A cosmic lighthouse

..and VERY cool

As the star rotates, we receive a periodic signal.

The beams can be x-rays from a hot spot a the surface, or radio light emitted at the magnetic caps of the neutron star,

2. Observations of Neutron Stars

2. Observations of Neutron Stars

Radio pulsars : Need a misalignment of the magnetic axis with respect to rotation axis to be able to detect it

2. Observations of Neutron Stars

Toys to observe radio pulsars

Big toys to observe radio pulsars2. Observations of Neutron Stars

As the star rotates, we receive a periodic signal from the it.

The beams can be radio light emitted at the magnetic caps of the neutron star, or x-rays from a hot spot a the surface

2. Observations of Neutron Stars

2. Observations of Neutron Stars

Extremely precise clocks

Spins down due to dipole radiation (plus GW, plus cooling, plus wind, sometimes)

218.8118438547254 ±0.0000000000009 Hz

3. Interior of Neutron Stars

3. Interior of Neutron Stars

Nuclear saturation

Fermi energy dominates over thermal energy: behaves as a cool body

3. Interior of Neutron Stars

Structure

Atmosphere : ~0.000001 m thick

Crust: 1-2 km thickCrystalline lattice of ions, which a sea of free electrons and neutronsElastic solidSuper duper smoothRotation can reach few % of the speed of light

3. Interior of Neutron Stars

Structure

Inner-crust / outer core :Density increases, more and more neutronsZero viscosityPasta phase

3. Interior of Neutron Stars

Pasta phase : Nuclei are no longer spherical

3. Interior of Neutron Stars

Outer core: superfluid of neutronsInner core : superconductor ?

3. Interior of Neutron Stars

Outer core: superfluid of neutronsInner core : superconductor ? Take away point:

We don’t know the equation of state of neutron star's interior.

We can’t reproduce these extreme environments in

laboratories

4. Glitches

4. Glitches

Sudden increase in spin frequency

Changes in frequency of the order of 10-5 to 10-12

~10% of observed pulsars have glitch every few years

L.M. Gonzalez-Romero, J.L. Blazquez-Salcedo 2009

4. Glitches

Sudden increase in spin frequency

Changes in frequency of the order of 10-5 to 10-12

~10% of observed pulsars have glitch every few years

4. Glitches

2 proposed models for glitches:

1. Star Quakes

2. Unpinned vortices

4. Glitches Model 1 : Star Quakes

Gravity wants the star to be spherical

Fast rotation of elastic crust makes the star oblate

4. Glitches Model 1 : Star Quakes

Stress builds up on the crust as the star spins down.Reaches eventually critical strain : need to readjust its

shape

4. Glitches Model 1 : Star Quakes

L = ѡ x I : if I goes down suddenly, ѡ goes up, hence the glitch

4. Glitches Model 1 : Star Quakes

Haskell & Melatos 2015

Oblateness

Total Energy, must be minimized while keeping L constant

Stress released in a crust quake

Waiting time until the next glitch

4. Glitches Model 1 : Star QuakesObservation : Vela pulsar

Chandra + HST

4. Glitches

2 proposed models for glitches:

1. Star Quakes

2. Unpinned vortices

Model 2 : Unpinned Vortices4. Glitches

Superfluid is irrotational

Boson condensate → quantum vortices

Quantum vortices carry quantized angular momentum

Model 2 : Unpinned Vortices4. Glitches

In superfluid, can change configuration of vortices and make vortices disappear

When nuclei are arounds, can’t reconfigure easily : vortices are pinned to nuclei

Glitch video

Summary

1. Figuring out the state of the matter in the interior of neutron stars is still a huge challenge

2. Pulsars glitch, and we are still not sure how this is happening

3. One of the model for glitches is crust quakes, but this model fails badly to explain some observations

ReferencesAndreas Reisenegger 2013, Magnetic fields of neutron stars , ApJ

http://www.cv.nrao.edu/course/astr534/PulsarTiming.html

Brynmor Haskell & Andrew Melatos, 2015 Models of Pulsar Glitches, ApJ

Vanessa Graber, Nils Andersson, Michael Hogg, 2016, Neutron Stars in the Laboratory, arXiv:1610.06882

Lorimer and Kramer, 2005, Handbook of pulsar astronomy, Cambridge University Press

William G. Newton, 2013, A Taste of Pasta?, Nature arXiv:0912.0628v1 [gr-qc] 3 Dec 2009L. M. Gonz ́alez-Romero and J. L. Bl ́azquez-Salcedo, 2009, Core-crust transition pressure evolution in post-glitch epoch for a Vela-type pulsar, arxiv.org/abs/0912.0628

http://chandra.harvard.edu

C. Reichhardt, 2001, Commensurate and Incommensurate Vortex Lattice Melting in Periodic Pinning Arrays, Physical Review B 64, 144509

3. Interior of Neutron Stars

Outer core: superfluid of neutronsInner core : superconductor ? What we need to pin down

EOS?:

More exotic pulsars (in terms of mass and/or binary system), or to see pulsars doing crazy

things

2. Observations of Neutron Stars

Pulsar timing: predicting the time of arrival of pulses

time

Period

2. Observations of Neutron Stars

Pulsar timing: predicting the time of arrival of pulses

time

Period

2. Observations of Neutron Stars

Pulsar timing:

Use phase coherence instead

Observe pulsar at regular interval

Measure precisely at what time the pulses arrive

Model arrival times of future pulses

Need to barycenter the data