HELIOSEISMOLOGY (I) STRUCTURE OF THE

• The Sun is the only for which we can measure internal properties → test of theory • acoustic mode Composition (heavy elements) from meteorites in the Sun • (p mode Density, internal rotation from n=14, l -20) • Central conditions from

HELIOSEISMOLOGY • The Sun acts as a resonant cavity, oscillating in mil- lions of (acoustic, ) modes (like a bell) → can be used to reconstruct the internal density struc- ture (like earthquakes on Earth) full-disk • oscillation modes are excited by convective eddies Dopplergram • periods of typical modes: 1.5 min to 20 min • velocity amplitudes: ∼ 0.1 m/s • need to measure Doppler shifts in spectral lines rela- tive to their width to an accuracy of 1:106 . possible with good spectrometers and long integra- tion times (to average out noise) Results • density structure, sound speed

• depth of outer convective zone: ∼ 0.28 R¯ velocity (km/s) • rotation in the core is slow (almost like a solid-body) → the core must have been spun-down with the enve- lope (efficient core–envelope coupling) rotation rate (nHz) r/R HELIOSEISMOLOGY (II) SOLAR The • • • • • • • • •

→ Sun tons H-burning lo tank sho -emitting rate Neutrinos, c they neutrino some The ev

ave e Homestak . . w ery + dir difficult the trinos reaction ergetic wn er ats 37 and of of can (exp Davis 7 NEUTRINOS e 1 neutrinos Cl than Be 2 H ct that exp absorption Chlorine mon → + carry + b pr can dete ected 1 e neutrinos erimen 8 reactions e e exp predicted ob H 37 B in generated − exp the observ ths Ar exp e ctor: b the → → → erimen e a of eriment n react + w e erimen neutrino detected (C um ach t a 8 7 2 e reactions the Sun) Be Li D ∼ y ed − 2 is underground b − Cl 2 3 + + in er: → t, with + 37 in only solar − × 0 in e

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neutrino n er e around ed energy filter pp um out = = to esc = 37 n exp 0 0 fluid) Cl filled c b 14 um . . hains) 86 the 42 ap e er a d (only eriments . atom 0 e b factor Mev released Mev of 1970) out pr Mev er: most from with the oblem 17) of minor neu- of 600 has the the en- in 3 The Davis Neutrino Experiment Proposed Solutions to the Problem

• dozens of solutions have been proposed

Model Predictions 1) Astrophysical solutions . require a reduction in central temperature of about 5 % (standard model: 15.6 × 106 K) . can be achieved if the solar core is mixed (due to convection, rotational mixing, etc.) . if there are no nuclear reactions in the centre (in- ert core: e.g. central black hole, iron core, degen- erate core) . if there are additional energy transport mecha- Homestake Mine nisms (e.g. by WIMPS = weakly interacting par- (with Cl tank) ticles) . most of these astrophysical solutions also change the density structure in the Sun → can now be ruled out by helioseismology 2) Nuclear physics . errors in nuclear cross sections (cross sections sometimes need to be revised by factors up to ∼ 100) . improved experiments have confirmed the nuclear cross sections for the key nuclear reactions Results 3) Particle physics Solar Neutrinos . all neutrinos generated in the Sun are electron neu- 12 10 trinos 1011 Solar Neutrino Spectrum pp Bahcall-Pinsonneault SSM 1010 . if neutrinos have a small mass (actually mass dif- 7Be 109 13 ferences), neutrinos may change type on their path N 108

/s/MeV) 15 between the centre of the Sun and Earth: 2 O 107 pep 17 neutrino oscillations, i.e. change from electron 106 F /s or /cm /s or 2 5 7 ¡ neutrino to or neutrinos, and then cannot be 10 Be 8B 104 detected by the Davis experiment Flux (/cm Flux 103 . vacuum oscillations: occur in vacuum hep 102 1 . 10 matter oscillations (MSW [Mikheyev-Smirnov-- 0.1 1.0 10.0 Neutrino Energy (MeV) Wolfenstein] effect): occur only in matter (i.e. as neutrinos pass through the Sun)

100 SNU RECENT EXPERIMENTS << Experiments >> SAGE GALLEX Combined • resolution of the neutrino puzzle requires more sensi- << SSM >> SSM Bahcall-Pinsonneault SSM tive detectors that can also detect neutrinos from the Turck-Chieze-Lopes SSM << NonSSM >> main pp-reaction S17 = Kam 18 TC = Kam 18 TC = Kam (S17 = 1.3) S34 = Kam 1) The Kamiokande experiment Dar-Shaviv Model Low Opacity (-20%)

Large S11 (Kam = 0.39) (also super-Kamiokande)

Large S11 (Kam = 0.57) Mixing Model (Kam = 0.44) Mixing Model (Kam = 0.53) MSW (Kam+Cl) I . uses 3000 tons of ultra-pure water (680 tons active

0 20 40 60 80 100 120 140 medium) for Gallium Rate (SNU) − −

+ e → + e (inelastic scattering)

. about six times more likely for e than and ¡

. observed flux: half the predicted flux (energy de- pendence of neutrino interactions?) The Sudbury Neutrino Observatory

2) The Gallium experiments (GALLEX, SAGE) . uses Gallium to measure low-energy pp neutrinos 1000 tons of heavy water directly 71 71 − e + Ga → Ge + e − 0.23 Mev . results: about 80 § 10 SNU vs. predicted 132 § 7 SNU (1 SNU: 10−36 interactions per target atom/s) 3) The Sudbury Neutrino Observatory (SNO) . located in a deep mine (2070 m underground)

. 1000 tons of pure, heavy water (D2O) . in acrylic plastic vessel with 9456 light sensors/photo- multiplier tubes . detect Cerenkov radiation of electrons and pho- tons from weak interactions and neutrino-electron scattering . results (June 2001): confirmation of neutrino os- cillations (MSW effect)?