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

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Presentation on theme: "COSMIC MAGNETIC FIELDS ElisaBete M. de Gouveia Dal Pino IAG-USP UFRRJ, October 2005."— Presentation transcript:

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 Magalhães 2005 B

8 Measuring Magnetic fields Zeeman effect (within galaxy): = e B /2 m e Polarized synchrotron emission (Beck and Krause 2005): I n CR B 1+α dl Faraday rotation of the diffuse polarized emission: RM n e B dl

9 Effelsberg VLA ATCA Some Radio Telescopes

10 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

11 PART I: Magnetic Fields in Stars and Compact Objetcs

12 Solar Magnetic Fields In corona (2 x 10 6 K): Magnetic arcs ( x 10 4 km) Sunspots (B = G)

13 Solar Magnetic Fields Magnetic arcs: rise by buoyancy due to convective motions (Parker-Rayleigh- Taylor instability) Silva, 2005 sunspot

14 Solar Flares Sudden release of erg (seconds to hours) Silva 2005

15 Solar Flares Flares energized by magnetic reconnection è E B released: heating, particle acceleration, coronal mass ejections (CMEs) Shibata et al. CMEs

16 Solar Flares Flares energized by magnetic reconnection è E B released: heating, particle acceleration, coronal mass ejections (CMEs) Shibata et al. CMEs

17 Solar Magnetic Fields 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 E B

18 Magnetic Field Evolution Fluid-B freezing diffusion diff = 4 L 2 >> 1 BA = constant

19 Dynamo Mechanism Responsible for conversion of E c E B -effect: turbulent/convection motions (B T B p ) -effect: v o =r differential rotation (B p B T ) = 1/4: magnetic diffusivity : field dissipation due to turbulent motion

20 Dynamo Mechanism -effect BpBp BTBT

21 Dynamo Mechanism -effect

22 Magnetic Fields in other stars Similar magnetic processes: in many stars (cool stars) Shibata 2005 STARS

23 ASTROPHYSICAL JETS EXTRAGALACTIC: 10 6 l.y., velocities c, source mass 10 8 M, L ~ erg/s Magnetic Fields in Jets Jet from Active Galactic Nuclei (AGN)

24 EXTRAGALACTIC: 10 6 l.y., velocities c, source mass 10 8 M, L ~ erg/s Magnetic Fields in Jets Jet from Active Galactic Nuclei (AGN)

25 Magnetic Fields in Jets GALACTIC: ~ 1 l.y., velocities c, source mass 10 M, L ~ erg/s

26 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

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 Shibata 2005 STARSDISKS Wind/Jet

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 II: Magnetic Fields in the ISM & Star Formation

32 ISM: Interstellar Medium

33 Effelsberg 21cm (Reich et al 2003) ISM 21cm Emission from Perseus - Auriga Polarized emission l=166° l=150° b=-4° b=+4°

34 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°

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 E B E turb E CR

36 Magnetic Fields in Molecular Clouds n(H 2 ) cm -3, N(H 2 ) , 13, B pos 140 G (Crutcher et al. 2004) Regular B and disk-like morphology L1544 Core

37 Magnetic Fields in Molecular Clouds L183 core DR21OH core n(H 2 ) , N(H 2 ) , B pos 0.7 mG (Lai et al. 2001) B los = 0.4, 0.7 mG B pos 0.7 mG n(H 2 ) , N(H 2 ) , 13, B pos 80 µG (Crutcher et al. 2004)

38 Magnetic Fields in Diffuse and Molecular Clouds H I Clouds Molecular Clouds B total ( G) – 3,000 M/(BA) <0.25 ~1 [B ] ~0 ~1/2 P thermal /P B P turbulent /P B Crutcher 2005

39 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

40 Star Formation in Molecular Clouds Observations consistent with approximate magnetic support in molecular cores ( g P B ) 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 (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

42 PART III: Magnetic Fields in the Milky Way

43 The Milky Way

44 Magnetic fields in our Galaxy Han et al ?

45 Equipartition fields in the Galaxy (Berkhuijsen, priv. comm.) Cosmic-ray energy density + radio synchrotron: 6 G and in inner region: 10 G Magnetic fields in our Galaxy

46 PART IV: Magnetic Fields in Galaxies, Clusters and IGM

47 Magnetic fields in Galaxies B 2 = B t 2 + B r 2 Polarized synchrotron: measures B r M51

48 Spiral patterns of regular B: observed in grand- design, flocculent and even in some irregular galaxies. Magnetic fields in Galaxies

49 Spiral patterns of regular B observed in Grand-design galaxies Magnetic fields in 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 flow around massive bars NGC1097 (Beck et al. 2004)

53 Organized B inside and outside of the circumnuclear ring ! Magnetic fields in Galaxies M31

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): = 9 μG Starburst galaxies: B μG Nuclear starburst regions: B 100μG! NGC1067: nuclear SB region Correlation B and SF!

56 Magnetic fields in Galaxies consistent with dynamo! E B E turb Outer regions: E B > E therm : B affects gas rotation curve !? (Battaner & Florido 2000)

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 z=5 kpc) Several halos: v / z < 0 contribute to excitation of dynamo! NGC5775 (Dettmar 2005)

59 Magnetic fields in Galaxy Halos B filaments and loops coupled with charged dust in halo! NGC891 (Rossa et al. 2005)

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 Rad/m/m+5000 Rad/m/m Hydra A Taylor & Perley (1993) Lane et al. (2004)

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 P B > P therm !

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! Numerical simulation (Kato et al 2005) Hydra

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 z=2.5): B IGM G, for L 1 Mpc

70 PART V: Primordial Magnetic Fields

71 Magnetic fields in Early Universe Universe History

72 Magnetic fields in Early Universe RMs of distant quasars (z>1) B in the past (Kronberg et al. 1992) 3C191 (z=1.945): B G in L 15 kpc (galaxy size!) B G Young spiral galaxy (z=0.395): What is the origin of these B fields in early Universe ?

73 B prim,o 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 L 2 >> t o BA = constant Alternative to dynamo: If B is primordial B gal G results from compression of primordial B:

74 Primordial Magnetic fields? Constraints: CMBR: Primordial B would influence CMBR via: breaking spatial isotropy MHD effects temperature and polarization fluctuations CMBR CMB spectrum B o ( 50 Mpc ) < –10 -9 G BB Nucleosynthesis: Primordial B could change expansion rate of the Universe and 4 He abundance BBN B(100pc, T=10 9 K) < G B o (1Mpc)< G

75 Primordial Magnetic fields? CMBR and BBB constraints: Imply B strengths the required by IGM today diff >> t o : diffusion length l o < 10 9 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): B o (1Mpc) G! Too small to seed galactic dynamo QCD Phase transition (quarks combine to form hadrons, T= K): B o (100kpc) G (under extreme conditions! Sigl et al.) Biermann Batery ( px n0): B o G (pre-galactic seed field is exponentially amplified by dynamo) Harrison effect: B o 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 Km 2 (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 (>10000) 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 -effect BpBp BTBT

84 Magnetic fields at Early Universe RMs of distant quasars (z>1) B in the past (Kronberg et al. 1992) 3C191 (z=1.945): B G in L 15 kpc (galaxy size!) B G Young spiral galaxy (z=0.395): What is the origin of these B fields in early Universe ?

85 Athreya et al 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.


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