Neutrina z supernowych

Transkrypt

1 Neutrina z supernowych v Obserwacja neutrin z SN1987A - czyli spoza naszej Galaktyki! v Kolaps grawitacyjny v Czego dowiedzieliśmy się o neutrinach v Szanse przyszłych obserwacji neutrin z supernowych

2 Natural sources of neutrinos at 10 kpc i.e. Galaxy center

3

4 Previous Supernovae observed in our Galaxy The most recent SN visible with the bare eye was observed by Kepler in 1604 yellow Hubble (visible) red Spitzer (infrared) green/blue Chandra (rtg)

5 Previous Supernovae observed in our Galaxy Only 8 supernovae have been observed in our Galaxy: Chinese records: 185, 386, 392 and 1006 Later: 1054, 1181, 1572, 1604 However all of them were relatively close to solar system. More distant SN are invisible hidden by interstellar gas Currently many SNs are observed in other gallaxies

6 Supernova 1987A Feb 1984 On Feb 23, 1987 a supernova was observed optically in the Large Magellanic Cloud at a distance of light years (50 kpc) At that time 2 large underground detectors searched for proton decays: Kamiokande and IMB. They inspected their data and found signals 4 hours earlier... Mar 8, 1987

7 Detector IMB

8 Observations of SN1987A IMB (Irvine-Michigan-Brookhaven) Raw data After standard analysis rejecting atmospheric muons

9 Neutrinos from Supernova 1987A in Kamiokande Universal time on Feb 23, 1987 Neutrinos arrived 3-4 hours earlier than photons because photons could not get through the outer layers of SN before they thinned enough.

10 IMB events

11 Observations of neutrinos from SN 1987A IMB Kamiokande Baksan LSD Location Ohio,US Japan Russia France (Mont Blanc) Detector type water Cerenkov liquid scintillator Detector mass (tons) Threshold(MeV) Number of events ??? Time of 1st 7:35:41 7:35:35 7:36:12 2:52:37 event (UT) Absolute time accuracy (sec) -54

12 Stellar evolution Interplanetary nebula Gravitation energy is transformed into heat; a gas-dust cocoon forms. Black Dwarf Protostar Stellar wind carries away a fraction of mass. Fusion reactions start changing H into He, a hydrostatic equilibrium sets in.. A large, dense, cool nebula (up to 10 6 M o, temp.~10 K) A gravitating matter condensation grows to ~ M o White Dwarf Star M ~ Red Giant M ~ 8M Neutron Star Energy supply is depleted, radiation pressure decreases. Stellar core contracts, its temperature grows, igniting hydrogen in the envelope. New energy supply leads to expansion of external layers. M ~ SN Red Super- Giant Increase of surface with a constant energy production rate leads to decreased power and envelope temperature. Black Hole M >> Stellar core contracts, temperature rises, making possible nuclear fusion of heavier elements.

13 Stellar Evolution

14 Stellar Dimensions 1. White dwarf 2. Red dwarf 3. Sun 4. Red Giant 5. Blue Giant The SN1987A progenitor was a blue supergiant

15 Road to gravitational collapse Main thermo-nuclear reactions: Reaction Ignition temp. (millions K) 4 1 H --> 4 He He --> 8 Be + 4 He --> 12 C C + 4 He --> 16 O 2 12 C --> 4 He + 20 Ne Ne + 4 He --> n + 23 Mg 2 16 O --> 4 He + 28 Si O --> 2 4 He + 24 Mg Si --> 56 Fe 6000 When mass of the iron core exceeds 1.4 solar masses the gravitation wins. SN produce much of the material in the universe. Heavy elements are only produced in supernovae, so all of us carry the remnants of these distant explosions within our own bodies. gravitational collapse

16 Gravitational Collapse

17 Neutrinos from Supernovae 56 Fe has maximum binding energy no more fusion and no more heat production When a core of iron reaches a Chandrasekhar mass of the gravitation wins and the core collapses Electrons of iron atoms are absorbed by protons: e + p ν + n prompt neutrinos e e Z νe + e e Z νµ + νµ e e Z ντ + e ν ν e τ neutron star 1.4 M Heat gives rise to gammas which produce e + e - pairs and then: thermal neutrinos

18 Expected SN neutrino properties Neutrino luminosity vs time E 53 B = 3 10 ergs Beacom and Vogel ν 17%, e ν 17%, e ν µ, ν µ, ντ, ντ 66% Thermal spectra (Fermi-Dirac distribution) Tν e = 3. 5MeV Tν e = 5MeV T 8. 0MeV " " = ν µ

19 Dane z IMB i Kamiokande: E vs czas Na wykresie przesunięto czas przyp. Kamiokande (w granicach błędu), tak aby pierwszy przyp. miał ten sam czas co w IMB. W wodzie najbardziej prawdop. oddziaływania to: + ν e + p e + n Progi detektorów: Kamiokande 7.5 MeV IMB 19 MeV Energia anty-ν równa się energii pozytronów ( energia widzialna Widać stygnięcie gwiazdy protoneutronowej

20 Dane z IMB i Kamiokande E vs kąt Distribution of the angle with respect to the direction from SN Isotropic distribution indicates mostly: + ν e + p e + n ν + e ν + e x rather than: (cross section smaller by orders of magnitude.) x However some anisotropy remains puzzling.

21 Neutrinos from gravitational collapse Occurs for a star heavier than 8 solar masses when its core exceeds Chandrasekar s limit of M=1.4 solar mass. A neutron star of a radius of r about 20 km is formed. The released energy is neutron star binding energy : E B = M 1 r 1 R M r = ergs (R r) 99% of this energy is carried away by neutrinos; neutrino luminosity L~ 3x10 53 ergs 1% goes into kinetic energy of the envelope particles Only 0.01% goes into light And yet it s ergs while our sun emits ergs/sec One SN shines as Suns!

22 Neutrinos from gravitational collapse Total neutrino luminosity L~ 3x10 53 ergs Prompt pulse lasts only several msec hence its total luminosity is small Almost all L is carried away by thermal neutrinos approximately obeying equipartition of energy : L( ν ) L( ν ) L( ν ) L( ν ) L( ν ) L( ν ) e e µ µ τ τ However energies of ν µ and ν τ are less degraded by interactions than that of ν e

23 Analysis of the observed signals Thermal neutrinos should be described by Fermi-Dirac distribution. Their fluence F (i.e. flux integrated over time): dφ= E = 2 const E de 3 T E 1+ exp( ) T 3.15 T T temperature E neutrino energy this spectrum was assumed for the analysis From the measurements of F on Earth one can calculate: 52 D 2 Φ L= ( ) T L in ergs Φ fluence in cm -2 T in MeV D distance in kpc

24 Neutrinos from SN 1987A- results Experiment: IMB Kamiokande Temperature (MeV) Fluence (x cm -2 ) Average energy (MeV) Total ν e energy (x10 52 ergs) Total energy released (x10 53 ergs) ± ± ± ± ± ± 1.5 Assuming :a) a distance of 49 kpc b)equipartition of energy between different flavors

25 What have we learned about neutrinos from SN1987A Lifetime τ > ( mν / ev) Mass m( ν ) < 11eV e sec For 2 neutrinos of energies E 1 (MeV) and E 2 (MeV) and the difference between their flight times δt (sec) their mass m (ev) : m 2 = 19.4 δt D 1 2 E E 2 where D (kpc) is the distance from the supernova. However one has to take into account a possibility that the time profile of the neutrino emission can mimick the pulse modulation due to the finite mass

26 What have we learned about neutrinos from SN1987A Magnetic moment 11 µν ( e) < µ B elmgt interaction would flip ν helicity into RH and ν would carry away energy without interacting - contrary to the observation that almost all the binding energy has been accounted for Q Q ν 17 Electric charge e < 1 10 a charged ν would experience an energy dependent delay due to its curved path in the intergalactic and galactic mgt field.

27 Test of equivalence principle The fact that the fermions (neutrinos) and bosons (photons) reached the Earth within 3 hours provides a unique test of the equivalence principle of general relativity. The gravitational field of our Galaxy causes a signifcant time delay, about 5 months, in the transit time of photons from the SN1987A. The observation of Feb. 23, 1987, proved that the neutrinos and the recorded photons are acted by the same gravitationally induced time delay within 0.5%

28 Actually neutrinos arrived earlier... about 3 hours earlier than light was observed. Photons had to wait until the envelope gets thin enough to pass through. Efekt OPERy : Δ υ ν c = 2, c Gdyby neutrina SN1987 były tak szybkie to przyleciałyby: δt = 2, i1, lat = 4 lata wcześniej czyli w 1983 r

29 SN1987A

30 SN 1987A Seven years later.. photos by Hubble Space Telescope

31 SN 1987A

32 Expected signals from future SN in Super-Kamiokande: Andromeda M31 Eg. for an SN in the Galactic center at 10 kpc: : : : 7300 oddz. ν e + p e + n 300 oddz. ν + e ν + e 100 oddz. ν e O e + X Hopefully other than electron antineutrinos could be studied. SN neutrinos are already flying to us

33 Expected signals from SN remnants (SNR neutrinos) Observation of a single SN relies on a very brief signal trivial separation from background but a very rare event. However the Universe is full of neutrinos from all previous SN flying around. One only needs to separate them from background of other neutrinos. The expected rate of SNR neutrinos is very model dependent but experimentally we may be close to detect them. arxiv:hep-ph/ arxiv:

34 Expected rate of gravitational collapse Estimates from: in Milky Way Historical observations: only 8 observed, however all within 5 kpc from the Sun (other obscured by dust in galactic disk). When one corrects for this and for the fact that not all observed SN resulted from core collapse one gets: one SN per 20 years Birth rate of pulsars model dependent: one SN per 10 or 100 years All pulsars result from core collapse, but not all SN leave a pulsar behind Oxygen abundance in the Galaxy: one SN per 10 years. Most of oxygen originates in core collapses.

35 Future observations of neutrinos from SN Ø Super-Kamiokande can see a few neutrinos from the near-by galaxy, M31, in the Andromeda constellation, 2.1 million light years away Ø One SN in years in our Galaxy but mostly invisible in optical spectrum Ø For a Galactic SN thousands of events in SuperKamiokande Ø Network of instant SN warning exists to point telescopes in a SN direction. Experiments should minimize their dead time. Ø Possible observation of neutrinos from cumulated SNR Unique way to learn about collapsing mechanism and about neutrinos

36 Future observations of neutrinos from SN Eta Carinae is a massive and unstable star with strong stellar winds. Perhaps a future supernova?