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COSMIC MAGNETIC FIELDS

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Hydra A Taylor & Perley (1993) Lane et al. (2004) Rotation Measures in Irregular Clusters ... Hydra. Magnetic fields in IGM. B probably pervades entire Universe ... – PowerPoint PPT presentation

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Title: COSMIC MAGNETIC FIELDS


1
COSMIC MAGNETIC FIELDS
  • ElisaBete M. de Gouveia Dal Pino
  • IAG-USP
  • UFRRJ, October 2005

2
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 !
3
WHY MAGNETIC FIELDS?
Charged Particle ? Fluid immersed in B
v x B ? J x B
4
WHY MAGNETIC FIELDS?
Charged Particle ? Fluid immersed in B
v x B ? J x B
TENSION
PRESSURE
5
WHY MAGNETIC FIELDS?
Charged Particle ? Fluid immersed in B
v x B ? J x B
6
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.

7
Measuring magnetic fields
  • Polarization by aligned dust grains with B of
    ISM

B
Magalhães 2005
8
Measuring Magnetic fields
  • Zeeman effect (within galaxy)
  • ?? e B/2? me
  • Polarized synchrotron emission (Beck and Krause
    2005)
  • I ? ? nCR B-1a dl
  • Faraday rotation of the diffuse polarized
    emission
  • RM ? ? ne B dl

9
Some Radio Telescopes
VLA
Effelsberg
ATCA
10
Outline
  1. Magnetic Fields in Stars and Compact Objects
  2. Magnetic Fields in the ISM Star Formation
  3. Magnetic Fields in the Milky Way
  4. Magnetic Fields in Galaxies, Clusters and
    IGM
  5. Primordial Magnetic Fields
  6. Future Needs and Perspectives

11
PART IMagnetic Fields in Stars and Compact
Objetcs
12
Solar Magnetic Fields
In corona (2 x 106 K) Magnetic arcs (30-100 x
104 km) Sunspots (B 100-2000 G)
13
Solar Magnetic Fields
Silva, 2005
Magnetic arcs rise by buoyancy due to convective
motions (Parker-Rayleigh-Taylor instability)
sunspot
14
Solar Flares
Silva 2005
Sudden release of 1030-1032 erg (seconds to hours)
15
Solar Flares
CMEs
Shibata et al.
  • Flares energized by magnetic reconnection
  • EB released heating, particle acceleration,
    coronal mass ejections (CMEs)

16
Solar Flares
CMEs
Shibata et al.
  • Flares energized by magnetic reconnection
  • EB released heating, particle acceleration,
    coronal mass ejections (CMEs)

17
Solar Magnetic Fields
What is the origin of solar magnetic activity?
Dynamo action ? Conductive ionized flow ?
Convective and turbulent motions ? Differential
rotation
Conversion of kinetic energy of these motions
into EB
18
Magnetic Field Evolution
Fluid-B freezing
diffusion
?diff 4?? L2 gtgt 1
? ? BA constant
19
Dynamo Mechanism
Responsible for conversion of Ec ? EB
? 1/4?? magnetic diffusivity ? field
dissipation due to turbulent motion
?-effect vo?r differential rotation (Bp ? BT)
?-effect turbulent/convection motions (BT ? Bp)
20
Dynamo Mechanism
Bp
?-effect
BT
?-effect
21
Dynamo Mechanism
?-effect
?-effect
22
Magnetic Fields in other stars
Similar magnetic processes in many stars (cool
stars)
Shibata 2005
STARS
23
Magnetic Fields in Jets
ASTROPHYSICAL JETS
Jet from Active Galactic Nuclei (AGN)
  • EXTRAGALACTIC ? 106 l.y., velocities ? c,
    source mass ?108 M?, L 1043 - 1048 erg/s

24
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

25
Magnetic Fields in Jets
GALACTIC 1 l.y., velocities ? c, source mass
?10 M?, L 1039 erg/s
26
Jets What are they?
Supersonic collimated outflows carry mass,
momentum, energy and magnetic flux from stellar,
galactic and extragalactic objects to the outer
medium
EXTRAGALACTIC
GALACTIC
27
WHAT IS THE JET ORIGIN ?
Magneto-centrifugal acceleration out off
accretion disk around the source (Blandford
Payne)
28
  • Accretion Disks

29
Magnetic Fields in Accretion Disks
Similar magnetic processes in stars in
accretion disks, galactic disks
Wind/Jet
Shibata 2005
STARS
DISKS
30
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)
31
PART IIMagnetic Fields in the ISM Star
Formation
32
ISM Interstellar Medium
33
ISM 21cm Emission from Perseus - Auriga
b4
b-4
l150
l166
Polarized emission
Effelsberg 21cm (Reich et al 2003)
34
ISM 21cm Emission from Perseus - Auriga
b4
  • ISM diffuse polarized emission traces B
    structures of pc and sub-pc sizes
  • Carries information about the turbulent ISM

b-4
l150
l166
Polarized emission
Effelsberg 21cm (Reich et al 2003)
35
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

36
Magnetic Fields in Molecular Clouds
L1544 Core
n(H2) ? 5 ? 105 cm-3, N(H2) ? 4 ? 1022, ?? ? 13?,
Bpos ? 140 ?G (Crutcher et al. 2004)

Regular B and disk-like morphology
37
Magnetic Fields in Molecular Clouds
DR21OH core
L183 core
Blos 0.4, 0.7 mG
Bpos ? 0.7 mG
n(H2) ? 3 ? 105, N(H2) ? 3 ? 1022, ?? ? 13?,
Bpos?80 µG (Crutcher et al. 2004)
n(H2) ? 2 ? 106, N(H2) ? 3 ? 1023, Bpos ? 0.7 mG
(Lai et al. 2001)
38
Magnetic Fields in Diffuse and Molecular Clouds
  • H I Clouds Molecular Clouds
  • Btotal (?G) 6.0?1.8 10 3,000
  • M/(BA) lt0.25 1
  • B ? ?? 0 1/2
  • Pthermal/PB 0.29 0.04
  • Pturbulent/PB 1.3 0.7

Crutcher 2005
39
Magnetic Fields in Diffuse and Molecular Clouds
  • Diffuse ISM and HI clouds dominated by turbulence

Parker 1972
Molecular clouds formed by HI clouds
accumulation along field lines
Crutcher 2005
40
Star Formation in Molecular Clouds
  • Observations consistent with approximate magnetic
    support in molecular cores (?g??PB)
  • 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!)
41
Phases of Star Formation
(a) Formation of cores in giant molecular clouds
by ambipolar diffusion and decay of turbulence
?t 1 3 Myr
(b) Rotating, magnetized gravitational collapse
?t ?
(c) Strong jets bipolar outflows reversal of
gravitational infall ?t 0.1 0.4 Myr
  • (d) Star and protoplanetary disk with lifetime
  • ?t 1 5 Myr

Shu, Adams, Lizano 1987
42
PART IIIMagnetic Fields in the Milky Way
43
The Milky Way
44
Magnetic fields in our Galaxy
?
Han et al. 2001
45
Magnetic fields in our Galaxy
Cosmic-ray energy density radio synchrotron
ltBgt ?6 ?G and in inner region ltBgt ?10 ?G
Equipartition fields in the Galaxy (Berkhuijsen,
priv. comm.)
46
PART IVMagnetic Fields in Galaxies, Clusters
and IGM
47
Magnetic fields in Galaxies
  • B2 Bt2 Br2

Polarized synchrotron measures Br
M51
48
Magnetic fields in Galaxies
  • Spiral patterns of regular B
  • observed in grand-design, flocculent and even in
    some irregular galaxies.

49
Magnetic fields in Galaxies
  • Spiral patterns of regular B observed in
  • Grand-design galaxies

M51
50
  • Flocculent galaxies
  • spiral field without
  • spiral arms !

NGC4414 (Soida et al. 2002)
51
  • Large
  • Irregulars
  • some
  • traces of
  • spiral field

NGC4449 (Chyzy et al. 2000)
52
  • Barred Spiral galaxies
  • Regular fields follow the shearing gas
    flowaround massive bars

NGC1097 (Beck et al. 2004)
53
Magnetic fields in Galaxies
M31
Organized B inside and outside of the
circumnuclear ring !
54
Magnetic fields in Galaxies
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
55
Magnetic fields in Galaxies
  • Survey of 74 S galaxies (Niklas)
  • ltBtotgt 9 µG
  • Starburst galaxies
  • B 30 - 50µG
  • Nuclear starburst regions
  • B 100µG!

Correlation B and SF!
NGC1067 nuclear SB region
56
Magnetic fields in Galaxies
Outer regions EB gt Etherm B affects gas
rotation curve !? (Battaner Florido 2000)
? consistent with dynamo!
EB Eturb
57
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
58
Magnetic fields in Galaxy Halos
B in Halos of galaxies with high SFR correlated
to diffuse ionized gas and X-rays (up to z5
kpc) Several halos ?v?/?z lt 0 ?contribute to
excitation of dynamo!
NGC5775 (Dettmar 2005)
59
Magnetic fields in Galaxy Halos
NGC891 (Rossa et al. 2005)
B filaments and loops coupled with charged dust
in halo!
60
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)

61
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?)

62
Dynamo in Galaxies
Beck 2005
63
Magnetic fields in Clusters
A 2029 Coma
64
Rotation Measures in Clusters
RMs of polarized synchrotron radiation from
background or embedded radio galaxies
65
Rotation Measures in Regular Clusters
Hydra A Taylor Perley (1993)
Lane et al. (2004)
-12000 Rad/m/m
5000 Rad/m/m
66
Rotation Measures in Irregular Clusters
A400 (3C75) Eilek Owen (2002)
-170 Rad/m/m
170 Rad/m/m
67
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 gt Ptherm!
68
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!
Hydra
Numerical simulation (Kato et al 2005)
69
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 z2.5)

BIGM ? 10-9 G, for L ? 1 Mpc
70
PART VPrimordial Magnetic Fields
71
Magnetic fields in Early Universe
Universe History

72
Magnetic fields in Early Universe
  • RMs of distant quasars (zgt1) ? B in the past
    (Kronberg et al. 1992)
  • 3C191 (z1.945)

B ? 0.4 - 4 ?G in L ? 15 kpc (galaxy size!)
  • Young spiral galaxy (z0.395)

B ? 1 - 4 ?G
What is the origin of these B fields in early
Universe ?
73
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 gtgt to ? ? ? BA constant
  • Alternative to dynamo If B is primordial ? Bgal
    ?10-6 G results from compression of primordial
    B


Bprim,o ? 10-9 G !
74
Primordial Magnetic fields?
  • Constraints
  • CMBR Primordial B would influence CMBR via
  • ? breaking spatial isotropy
  • ? MHD effects temperature and
    polarization fluctuations CMBR

CMB spectrum ? Bo(50 Mpc) lt 10-8 10-9 G
  • BB Nucleosynthesis Primordial B could change
    expansion rate of the Universe and 4He abundance

BBN ? B(100pc, T109K) lt 1011 G ?
Bo(1Mpc)lt10-10 G
75
Primordial Magnetic fields?
  • CMBR and BBB constraints
  • Imply B strengths ? the required by IGM today
  • ?diff gtgt to diffusion length lo lt 109 cm
  • Small scale fields produced in early Universe
    survived and left no significant imprints on BBN
    or CMB (perhaps!)

76
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 (?px?n?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)

77
Future Needs Perspectives
  • Higher radio polarization sensitivity
  • Higher angular resolution (to map wealth of
    magnetic structures in galaxies)

Beck 2005
78
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).

79
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 (gt10000)

Cordes 2001
80
Square Kilometer Array (SQA)
Magnetic Fields in the Universe from Laboratory
and Stars to primordial Structures
American Inst. Phys., Conf. Procs., AIP, vol. 784
81
Square Kilometer Array (SQA)
Thank you !
82
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
83
Dynamo Mechanism
Bp
?-effect
BT
?-effect
84
Magnetic fields at Early Universe
  • RMs of distant quasars (zgt1)
  • ? B in the past (Kronberg et al. 1992)
  • 3C191 (z1.945)

B ? 0.4 - 4 ?G in L ? 15 kpc (galaxy size!)
  • Young spiral galaxy (z0.395)

B ? 1 - 4 ?G
What is the origin of these B fields in early
Universe ?
85
Athreya et al. 1998
  • VLA observations of 15 radio galaxies with zgt2
  • Four gals show intrinsic RMs in excess of 1000
    rad m-2
  • The environs of the gals at zgt2 have B-fields
    with micro-G strength
  • Kim 2005.
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