Effects of mirror dark matter on neutron starsnautilus.fis.uc.pt/compstar/_inc/download_lectures.php...FREDRIK SANDIN IFPA, Département AGO, Université de Liège Talk given at the

FREDRIK SANDIN

IFPA, Département AGO, Université de Liège

Talk given at the second workshop of CompStar, Coimbra, Feb 2009

Effects of mirror dark matter on neutron stars

F.S. & P. Ciarcelluti [arXiv:0809.2942]

Fredrik Sandin Efects of mirror dark matter on neutron stars

Motivation

Dark matter apparently is thedominating form of matter in galaxies

How does it affect neutron stars – dowe need to be concerned?


Main potential effects of dark matter

Accretion → heating / collapse

Lower critical mass for core collapse

Non-uniqueness of equilibrium sequence


Outline

Introduction

Mirror-matter hypothesis

Mass-radius relation

Critical mass

Heating


Dark matter – a few reminders

Motivated by rotation of galaxies, lensingand cosmological concordance (CMB, large-scalestructure, BBN, .)

CDM: 4% atoms 22% dark matter 74% dark energy

Cannot be explained with standard-model particles

Popular hypothesis: WIMPs, e.g., supersymmetry→ neutralinos with m ~ 100 GeV … TeV

For each boson there is a corresponding fermion, and vice versa

Symmetry is broken, s-particles must be massive

DM should accumulate in stellar objects (?)


Effects of WIMPs on NS

Bertone & Fairbairn PRD 77, 043515 (2008)

See also Gould, Draine, Romani & Nussinov PLB 238, 337 (1990) Goldman & Nussinov, PRD 40, 3221 (1989)

Captured WIMPs should not collapse NS


Effects of WIMPs on NS

Kouvaris PRD 77, 023006 (2008)c

Heating from annihilation of WIMPs Steady state surface temperature ~104 K or less

Mass of WIMP-core too low to affect structure of NS WIMPs either self-annihilate at sufficient rate

or collapses the star (Mmax

~ Mplanet

)


What about other dark-matter candidates?

WIMP-picture of dark matter could be oversimplified For a recent review see Perivolaropoulos, “Six Puzzles

for LCDM Cosmology” [arXiv: 0811.4684]

Stable fermionic dark-matter particles predictedby some “hidden-sector” theories

Such particles could affect NS significantly


Mirror-matter hypothesis Consequence of parity-symmetry restoration

Lee & Yang (1956); Foot, Lew & Volkas, PLB 272 (1991)History & refs: Okun, Phys. Usp. 50 (2007); hep-ph/0606202

G → GO⊗G

M → two sectors: ordinary (O) and mirror (M)

Space-time is common to both sectors

Lagrangians identical in the two sectors

Mirror and ordinary particles interact by gravity

Feasible dark-matter candidate, studied in some detail

Cosmology requires different T and B in the two sectors

Helium dominated → different structure, evolution and stellar propert.

Some effects on neutron stars discussed in literatureKhlopov et al., Sov. Astron. 35, 21 (1991)


Hydrostatic equilibrium – a reminder

Ideal fluid in static isotropic spacetime

Einstein equation simplifies to

Tolman–Oppenheimer–Volkoff equation


Hydrostatic equilibrium

Ideal fluid in static isotropic spacetime

Einstein equation simplifies to

“Inertia”

Gravity, common to both sectors

Separation of hydrostatic equation


Mass-radius relation

Minimal parity-symmetric extension of SM

ℒM

= ℒO

→ Identical

EoS in the two sectors

DD2F EoS by S. Typelused here

Structure affected byfew % mirror baryons


Radii of typical NS and maximum mass

Accretion from mirror interstellar medium too slow to affect structure

Mirror baryons mustoriginate from the progenitor star or a binary companion


Critical mass for core collapse

Chandrasekhar mass is lowered Result for equal electron

fractions in the two sectors

For 50% mirror matterwe confirm estimate by

Kolb, Seckel & Turner,Nature 314, 415 (1985)

Effect on lightcurve?


Accretion of mirror matter: energy budget

1.4 Msun

, DO ~ 26 km

1% mirror baryons

DM ~ 10 km

1 mirror baryon falls from “infinity”

“long time”

Q ~ ?

Equilibriumconfiguration

NO

Equilibriumconfiguration

NO, N

M+1

NM



m=m0g00~940 eRM MeV~650MeV

m

Mirror baryon has kinetic energy 940 - 650 ~290 MeVon impact, which is emitted in the mirror sector

The mass-energy difference between initial and final configurations is

Gravitational binding energy in ordinary sectorpractically unchanged → no significant heating

The ordinary sector can be heated by weak interactions between the sectors (-' etc). If this heating is of order MeV, which seems optimistic, accretion from the mirror interstellar medium gives a steady-state surface temperature of at most 105 K

m0

1.4 Msun

, DO ~ 26 km

1% mirror baryons

DM ~ 10 km

∂M∂N M

~ 650MeVN O


Concluding remarks

Nature of dark matter is unknownExciting time! DAMA, XENON10, CDMS II, CRESST, Pamela, …

Mirror matter is a feasible dark-matter candidatethat could have significant effects on neutron stars

M-R relation & Chandrasekhar mass depend on Ndm

/ NO

Heating by dark-matter accretion seems irrelevant

Future work Effect of dark-matter core on SN lightcurve?

Dynamical effects of dark-matter core?


Density profiles for fixed NO



m

m0

1.4 Msun

, DO ~ 26 km

1% mirror baryons

DM ~ 10 km

Caution!

E=M c2=4c2∫0

Rdr r2 [O r M r ]

∂ EO∂N M

~−290MeV ,∂EM∂N M

~940MeV

E= EOEM“ “

N O N O


Cooling calculation

Simple homogenous cooling model

Steady-state surfacetemperature < 105 K

1.4 Msun

star with 1% mirror baryons

Shapiro & Teukolsky:

Estimate of maximum accretion rate for an NS in a dense mirror molecular cloud~106 kg/s

From Kouvaris PRD 77, 023006 (2008)

Documents

Effects of mirror dark matter on neutron starsnautilus.fis.uc.pt/compstar/_inc/download_lectures.php...FREDRIK SANDIN IFPA, Département AGO, Université de Liège Talk given at the