COSMIC MAGNETIC FIELDS ElisaBete M. de Gouveia Dal Pino IAG-USP UFRRJ, October 2005.

COSMIC MAGNETIC FIELDSCOSMIC MAGNETIC FIELDS

ElisaBete M. de Gouveia

Dal Pino

IAG-USP

UFRRJ, October 2005

PREAMBLE

Most of visible matter in the Universe is in plasma state:

composed of ionized or partially ionized gas permeated by magnetic

fields

Alfvén, Biermann, Chandrasekhar and Parker knew that decades ago !

WHY MAGNETIC FIELDS?

Charged Particle Fluid immersed in B

v x B J x B



v x B J x B

TENSION PRESSURE



v x B J x B

MAGNETIC FIELDS

Crucial in: star formation, solar and stellar activity, pulsars, accretion disks, formation and stability of jets, formation and propagation of cosmic rays, galaxy structure.

Probably crucial in: ISM, molecular clouds, supernova remnants, proto-planetary disks, and planetary nebulae, GRBs.

Importance not well understood in: stellar evolution, halos of galaxies, galaxy evolution, and structure formation in the early Universe.

Measuring magnetic fields

• Polarization: by aligned dust grains with B of ISM

Magalhães 2005

B

Measuring Magnetic fields• Zeeman effect (within galaxy):

= e B║/2 me

• Polarized synchrotron emission (Beck and Krause 2005):

I ∫ nCR B┴1+α dl

• Faraday rotation of the diffuse polarized emission:

RM ∫ ne B║ dl

Effelsberg

VLA

ATCA

Some Radio Telescopes

Outline

I. Magnetic Fields in Stars and Compact Objects

II. Magnetic Fields in the ISM & Star Formation

III. Magnetic Fields in the Milky Way

IV. Magnetic Fields in Galaxies, Clusters and IGM

V. Primordial Magnetic Fields

VI. Future Needs and Perspectives

PART I:

Magnetic Fields in Stars and Compact Objetcs

Solar Magnetic Fields

In corona (2 x 106 K):

Magnetic arcs (30-100 x 104 km)

Sunspots (B = 100-2000 G)


Magnetic arcs: rise by buoyancy due to convective motions (Parker-Rayleigh-Taylor instability)

Silva, 2005

sunspot

Solar Flares

Sudden release of 1030-1032 erg (seconds to hours)

Silva 2005

Solar Flares

Flares energized by magnetic reconnection

EB released: heating, particle acceleration, coronal mass

ejections (CMEs)

Shibata et al.

CMEs


Dynamo action:

Conductive ionized flow

Convective and turbulent motions

Differential rotation

What is the origin of solar magnetic activity?

Conversion of kinetic energy of

these motions into EB

Magnetic Field Evolution

Fluid-B freezing diffusion

diff = 4 L2 >> 1 BA = constant

Dynamo MechanismResponsible for conversion of Ec EB

-effect:

turbulent/convection motions (BT Bp)

-effect: vo=r differential rotation (Bp BT)

= 1/4: magnetic diffusivity

: field dissipation due to turbulent motion

Dynamo Mechanism

-effect

-effect

Bp

BT

Dynamo Mechanism

-effect -effect

Magnetic Fields in other stars

Similar magnetic processes: in many stars (cool stars)

Shibata 2005

STARS

ASTROPHYSICAL JETS

EXTRAGALACTIC: 106 l.y., velocities c, source mass 108 M, L ~ 1043 - 1048 erg/s

Magnetic Fields in Jets

Jet from Active Galactic Nuclei (AGN)

EXTRAGALACTIC: 106 l.y., velocities c, source mass 108 M, L ~ 1043 - 1048 erg/s


Jet from Active Galactic Nuclei (AGN)


GALACTIC:

~ 1 l.y., velocities c, source mass 10 M, L ~ 1039 erg/s

Jets: What are they?

EXTRAGALACTIC

GALACTIC

Supersonic collimated outflows carry:

mass, momentum, energy and magnetic flux from stellar, galactic and extragalactic objects to the outer medium

WHAT IS THE JET ORIGIN ?

Magneto-centrifugal acceleration out off accretion disk around the source (Blandford & Payne)

Accretion Disks

Magnetic Fields in Accretion Disks

Similar magnetic processes in stars: in accretion disks, galactic disks

Shibata 2005STARS DISKS

Wind/Jet

Magnetic Fields in Accretion Disks

X-ray and radio flares: ejections accelerated during violent magnetic reconnection (de Gouveia Dal Pino & Lazarian 2001, 2005; de Gouveia Dal Pino 2006)

PART II:

Magnetic Fields in the ISM & Star Formation

ISM: Interstellar Medium

Effelsberg 21cm (Reich et al 2003)

ISM 21cm Emission from Perseus - Auriga

Polarized emissionl=166° l=150°

b=-4°

b=+4°

Effelsberg 21cm (Reich et al 2003)

ISM 21cm Emission from Perseus - Auriga

Polarized emission

• ISM diffuse polarized emission: traces B structures of pc and sub-pc sizes

• Carries information about the turbulent ISM

l=166° l=150°

b=-4°

b=+4°

Magnetic fields in the ISM

• MHD turbulence distributes energy from SN explosions, jets and winds within the ISM

• Magnetic fields control density and distribution of cosmic rays in the ISM and halo

• EB Eturb ECR

Magnetic Fields in Molecular Clouds

n(H2) 5 105 cm-3, N(H2) 4 1022, 13, Bpos 140 G (Crutcher et al. 2004)

Regular B and disk-like morphology

L1544 Core

Magnetic Fields in Molecular Clouds

L183 coreDR21OH core

n(H2) 2 106, N(H2) 3 1023, Bpos 0.7 mG (Lai et al. 2001)

Blos = 0.4, 0.7 mG

Bpos 0.7 mG

n(H2) 3 105, N(H2) 3 1022, 13, Bpos80 µG (Crutcher et al. 2004)

Magnetic Fields in Diffuse and Molecular Clouds

H I Clouds Molecular Clouds

Btotal (G) 6.01.8 10 –

3,000

M/(BA) <0.25 ~1

[B ] ~0 ~1/2

Pthermal/PB 0.29 0.04

Pturbulent/PB 1.3 0.7

Crutcher 2005

Magnetic Fields in Diffuse and Molecular Clouds

• Diffuse ISM and HI clouds: dominated by turbulence

Molecular clouds: formed by HI clouds accumulation along field lines

Parker 1972

Crutcher 2005

Star Formation in Molecular Clouds

• Observations consistent with approximate magnetic support in molecular cores

(gPB)

• Ambipolar diffusion driving star formation on a fast (~few free-fall times) timescale

Li & Shu (1996)

Magnetic fields also essential for removal of angular momentum from protostellar cloud (magnetic braking!)

Phases of Star Formation

(d) Star and protoplanetary disk with lifetime:

Δt = 1 – 5 Myr

(a) Formation of cores in giant molecular clouds by ambipolar diffusion and decay of turbulence:

Δt = 1 – 3 Myr

(b) Rotating, magnetized gravitational collapse:

Δt = ?

(c) Strong jets & bipolar outflows; reversal of gravitational infall:

Δt = 0.1 – 0.4 Myr

Shu, Adams, & Lizano 1987

PART III:

Magnetic Fields in the Milky Way

The Milky Way

Magnetic fields in our Galaxy

Han et al. 2001

?

Equipartition fields in the Galaxy (Berkhuijsen, priv. comm.)

Cosmic-ray energy density + radio synchrotron:

<B> 6 G

and in inner region:

<B> 10 G

Magnetic fields in our Galaxy

PART IV:

Magnetic Fields in Galaxies, Clusters and

IGM

Magnetic fields in Galaxies

B2 = Bt2 + Br

2

Polarized synchrotron: measures Br

M51

Spiral patterns of regular B:

observed in grand-design, flocculent and even in some irregular galaxies.


Spiral patterns of regular B observed in

Grand-design galaxies


M51

Flocculent galaxies:spiral field without

spiral arms !

NGC4414NGC4414(Soida et al. 2002)

Large

Irregulars:

some

traces of

spiral field

NGC4449NGC4449(Chyzy et al. 2000)

Barred Spiral galaxies:

Regular fields follow the shearing gas flowaround massive bars

NGC1097(Beck et al. 2004)

Organized B inside and outside of the circumnuclear “ring” !


M31


Turbulent fields are strongest in spiral arms (20 G): due to intense star formation, SN shocks.

Regular fields are strongest in interarm regions (15 G)

M51

Magnetic fields in Galaxies• Survey of 74 S galaxies (Niklas):

<Btot> = 9 μG

• Starburst galaxies:

B ≥ 30 - 50μG

• Nuclear starburst regions:

B ≥ 100μG!

NGC1067: nuclear SB

region Correlation B and SF!


consistent with dynamo!EB ≈ Eturb

Outer regions:

EB > Etherm :

B affects gas rotation curve !?

(Battaner & Florido 2000)

M31: very regular (coherent) field revealed by Faraday rotation

The coherent

magnetic field

in M31 is the

best evidence

so far for

dynamo action !

Fletcher et al. 2004

Magnetic fields in Galaxy Halos

B in Halos of galaxies with high SFR:correlated to diffuse ionized gas and X-rays (up to z=5 kpc)

Several halos:

v/z < 0

contribute to excitation of dynamo!

NGC5775 (Dettmar 2005)

Magnetic fields in Galaxy Halos

B filaments and loops coupled with charged dust in halo!

NGC891 (Rossa et al. 2005)

Do dynamos work in galaxies ?

YES:+ Spiral fields occur almost everywhere, even in

irregular galaxies and central rings

++ Magnetic arms occur between gas arms

++ Large-scale coherent fields exist

++ There is at least one case of a dominating axisymmetric mode (M31)

Do dynamos work in galaxies ?

NO:

- Single dominating modes are rare (nonlinear multiple dynamos? – Subramanian 1988)

- Coherent fields surprisingly weak in galaxies with strong density waves (M51) (strong compression and/or shear?)

- Spiral fields extend well into the centers - Fields are still strong in outer regions of galaxies

(magneto-rotational instability?)

Dynamo in Galaxies

Beck 2005

Magnetic fields in Clusters

A 2029 Coma

Rotation Measures in Clusters

RMs of polarized synchrotron radiation from background or embedded radio galaxies

Rotation Measures in Regular Clusters

-12000 Rad/m/m +5000 Rad/m/m

Hydra A Hydra A Taylor & Perley (1993)Taylor & Perley (1993)

Lane et al. (2004)Lane et al. (2004)

Rotation Measures in Irregular Clusters A400 (3C75) A400 (3C75) Eilek & Owen (2002)Eilek & Owen (2002)

-170 Rad/m/m +170 Rad/m/m

Magnetic fields in Clusters

• X-rays observations Abel clusters (e.g., Grasso & Rubinstein 2001):

• Coma cluster: B 8.3 G ! (tangled in L ~1 kpc)

• Clusters central regions with radio sources (Govoni et al. 2005):

B 5-30 G PB > Ptherm!

Origin of B in Clusters ?

B fields powered by jets from radio sources (Colgate & Li 2003, Kato et al. 2005).

But: pre-existing B may be required!

Numerical simulation (Kato et al 2005)

Hydra

Magnetic fields in IGM

• B probably pervades entire Universe

• IGM: rarefied ionized gas and coherence L of B poorly known

• Faraday rotation of polarized emission from distant quasars (up to z=2.5):

BIGM 10-9 G, for L 1 Mpc

PART V:

Primordial Magnetic Fields

Magnetic fields in Early Universe

Universe History

Magnetic fields in Early Universe

RMs of distant quasars (z>1) B in the past (Kronberg et al. 1992)

• 3C191 (z=1.945):

B 0.4 - 4 G in L 15 kpc (galaxy size!)

B 1 - 4 G

• Young spiral galaxy (z=0.395):

What is the origin of these B fields in early Universe ?

Bprim,o 10-9 G !

Primordial Magnetic fields?

Strong B in galaxy clusters and in galaxies at high redshifts:

Are the magnetic fields primordial ?

Pros:

Large conductivity of plasma in Universe:

diff = 4 L2 >> to BA = constant

Alternative to dynamo: If B is primordial Bgal 10-6 G results from compression of primordial B:


Constraints:

• CMBR: Primordial B would influence CMBR via:

breaking spatial isotropy

MHD effects temperature and polarization fluctuations CMBR

CMB spectrum Bo(50 Mpc) < 10-8 –10-9 G

• BB Nucleosynthesis: Primordial B could change expansion rate of the Universe and 4He abundance

BBN B(100pc, T=109K) < 1011 G

Bo(1Mpc)<10-10 G


CMBR and BBB constraints:

Imply B strengths the required by IGM today

diff >> to: diffusion length lo < 109 cm:

Small scale fields produced in early Universe survived and left no significant imprints on BBN or CMB (perhaps!)

Models for Primordial Magnetic fields

• Inflation (breaking conformal invariance of

electromagnetic field): Bo(1Mpc) 10-62 G! Too small to seed galactic dynamo

• QCD Phase transition (quarks combine to form

hadrons, T= 1.5 1012 K): Bo(100kpc) 10-9 G (under extreme conditions! Sigl et al.)

• Biermann Batery (pxn≠0): Bo 10-21 G (pre-galactic seed field is exponentially amplified by dynamo)

• Harrison effect: Bo 10-19 G (pre-galactic

seed field is amplified by dynamo)

• SN-driven turbulence (may amplify seed B-fields in 10 Myr only; Kim 2005)

Future Needs & Perspectives

• Higher radio polarization sensitivity

• Higher angular resolution (to map wealth of magnetic structures in galaxies)

Beck 2005

Square Kilometer Array (SKA)

• Total effective collecting area: 1 Km2 (100 MHz to 25 GHz)

• Stations of ~100 m diameter 150 stations – accounting for half the SKA area – will be distributed across continental distances (~3000 km).

• Remaining area will be concentrated within a central region of 5 km diameter (2020).

Square Kilometer Array (SKA) Map nearby galaxies 10x better angular resolution of present radio telescopes

10x more distant galaxies with similar spatial resolution as today

detect synchrotron emission from galaxies and structures in the earliest stage of evolution

search for the earliest magnetic fields and their origin

proto-planets

black-holes

pulsars (>10000)

Cordes 2001

Square Kilometer Array (SQA)

Magnetic Fields in the Universe: from Laboratory and Stars to

primordial Structures

American Inst. Phys., Conf. Procs., AIP, vol. 784

Square Kilometer Array (SQA)

Thank you !

Origin of B in Clusters ?

B fields powered by jets from radio sources (Colgate & Li 2003, Kato et al. 2005). But pre-existing B may be required!

Kato et al 2005

Dynamo Mechanism

-effect

-effect

Bp

BT

Magnetic fields at Early Universe

RMs of distant quasars (z>1)

B in the past (Kronberg et al. 1992)

• 3C191 (z=1.945):

B 0.4 - 4 G in L 15 kpc (galaxy size!)

B 1 - 4 G

• Young spiral galaxy (z=0.395):

What is the origin of these B fields in early Universe ?

Athreya et al. 1998

•VLA observations of 15 radio galaxies with z>2•Four gals show intrinsic RMs in excess of 1000 rad m-2

•The environs of the gals at z>2 have B-fields with micro-G strength• Kim 2005.

COSMIC MAGNETIC FIELDS ElisaBete M. de Gouveia Dal Pino IAG-USP UFRRJ, October 2005.

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Transcript of COSMIC MAGNETIC FIELDS ElisaBete M. de Gouveia Dal Pino IAG-USP UFRRJ, October 2005.