An Introduction to Supernovae. Ewald Müller Max-Planck Institut für Astrophysik

Transcription

1 An Introduction to Supernovae Ewald Müller Max-Planck Institut für Astrophysik

2 E S O -V LT Crab nebula with pulsar (constellation Orion) Remnant of a supernova observed in the year 1054

3 A New Star, as bright and as red as Mars, was discovered on October , close to the position where another astrologically significant event was taking place, the conjunction of Mars and Jupiter. The New Star created a stir throughout Europe. At Padua the new star was observed by Galileo, while in Prague Kepler made careful observations and the Supernova now carries his name. Galileo gave 3 public lectures that were attended by a large audience in which he demonstrated that the new star was much further than the moon. This had important astronomical consequences since it showed that change occurrs in the sky, contrary to the theory of Aristotle and his followers.

4 SN 1604 composite image: X-ray (Chandra, green-blue) optical (HST, yellow) IR (SST, red) Last observed galactic supernova! Note: first use of a telescope for astronomical purpose by Galileo Galilei in 1609!

5 Cassiopeia A: Remnant of a supernova exploded around 1680 C h a n d ra : X -ra y c o m p o s ite im a g e central X-ray point source found in 2000 by Chandra: a neutron star? X-ray images in different lines (Si, Ca & FeK)

6 Cas A composite image: X-ray (Chandra, green-blue), optical (HST, yellow) & IR (SST, red)

7 Supernovae in the Milky Way during the last millenium date visible for 1006 some years 1054 about 2 years months ~1300? months 1604 about 1 year ~1680? >18 years 1 distance observed in/by far east, Arabia, St.Gallen far east, Arabia China, Japan? (RX J ) Tycho Brahe Johannes Kepler Flamsted? (Cas A) Ian Shelton Number of observed extragalactic supernovae: > 3100 (since 1885)

8 30 Doradus region in the Large Magellanic Cloud (d ~ light years) - Blue Supergiant Sandulek Supernova 1987A 7:35 UT

9 - Supernova 1987A environment & ring system

10 Supernova 1987A: Blast wave encountering the inner ring -

11 ROSAT X-ray image of Vela (d ~500pc) & Puppis (d~2kpc) SNR Age of Vela SNR ~11000 yrs angular size: ~ 8o (ie. ~16 x size of moon) credit: Aschenbach et.al 1995, Nature 373, 587

12 ROSAT X-ray observations at low energy & high energy reveal three (!) partially overlapping SNRs: Vela, Puppis A & Vela Jr. (RX J ) (Aschenbach 1998, Nature 396, 141)

13 credit: W.P.Blair (John Hopkins Univ., Baltimore, USA)

14 CANDRA X-ray image of immediate neighbourhood of Vela pulsar ROSAT X-ray picture with labeled protrusions credit: Aschenbach et.al 1995, Nature 373, 587 (region would be barely visible on neigbouring ROSAT image!)

15 ESO-VLT: NGC 6118 & SN2004dk ( d ~ 25 Mpc, Ib/c)

16 SN 1993J in M81: Evolution of the radio remnant (MERLIN)

17 SN 1993J in M81 (d = 3.7 Mpc) Evolution of the radio remnant (MERLIN) * March 28, 1997 red supergiant progenitor identified (2nd time in history!) ejecta too rich in He & bizarre light curve --> binary system?

18 HST ACS/HRC INT, LaPalma Site of SN 1993J HST WFPC2 credit: ESA & J.R.Maund

19 blue companion star discovered 10 years after explosion by HST light echo Close-up of SN 1993J explosion site (credit: ESA & J.R.Maund)

20 SN 1993J exploding (artist's impression) [ credit: ESA & J.R.Maund ]

21 T y p e Ia s u p e rn o va a t z =

22 Supernova botanics according to spectra & light curves

23 Supernova light curves pronounced maximum after 2-3 weeks exponential tail (radioactive decay of 56 Ni 56Co 56Fe) maximum brightness largest for SNe Ia only SNe Ia form a (quite) homogeneous class standard candles!? possibility to measure expansion of universe

24 Supernova spectra discriminate types (no spectrum no type!!) provide information about - stellar & explosive nucleosynthesis - abundances and chemical stratification (tomography) - stellar environment & progenitor star

25 Number of supernovae per year as function of survey distance Milky way: 2.4 supernovae/century (70% CCSN) (Arnaud etal '04) (none in Milky way since 1680 & none in Andromeda since 1885)

26 Observational facts - very bright event: L ~ 1010 Lsun - fast expanding ejecta: v ~ 104 km/s - energies: electromagnetic: ~ 1049 erg ~ 1051 erg kinetic: neutrinos (SN1987A): ~ erg - progenitor star distroyed (SN 1987A, SN 1993J) - freshly synthesized 56Ni (0.07Msun in SN1987A; (not SNe Ia) Msun in SNe Ia) - neutron stars in (some) SNRs - neutron star kicks (up to 1000km/s!) (not SNe Ia)

27 energy sources for a supernova explosion thermonuclear energy (SNe Ia) conversion of ~1 solar mass of He, C or O into iron group nuclei --> E ~ 1051erg gravitational binding energy (SNe II, Ib, Ic) formation of a compact object of ~1 solar mass with a radius ~10km --> E ~ erg

28 Supernova classification according to physical processes

29 Importance of Supernovae: Universal players in - nucleosynthesis (we are star dust) 1 - star formation (including the solar system) - evolution of the ISM (energizing, mixing, ejection) - production of cosmic rays (up to 30% of SN energy)

30

31 Onion-like structure of a CCSN progenitor several million years after its birth: mass: Msun radius: Rsun O C Si He H - shells of different composition are separated by active thermonuclear burning shells - core Si-burning leads to formation of central iron core Note: figure not drawn to scale!

32 Observational evidence for large scale mixing in SN 1987A 1

33 Observational evidence for a globally anisotropic explosion SN1987A: ejecta are non-spherical (Wang et al. 2002)

34 Further evidence for non-spherical core collapse supernova explosions indirect: - large pulsar velocities - association with long GRBs - asymmetries in late-time emission-line profiles of SNe Ic direct: - spectropolarimetry of SNe Ic & SNe II-P (SN2004dj, 3.1Mpc; Leonhard et al. '06) Vela SNR: protrusions, fast pulsar progenitor: super giant in compact star cluster (Sandage's star 96), ~12 Msol (Wang et al. '05)

35 Blue Giant k (Red Giant: 100) m Fe-Ni core Observing the Surface: CCSN length scale problem km Neutron star 0k m

36 Looking into the heart of a core collapse supernova - through observations of neutrinos (up to now only SN1987A) - th ro u g h o b s e rva tio n s o f g ra vita tio n a l w a ve s (n o t y e t o c c u re d! W o u ld p ro vid e kin d o f R o s e tta s to n e!) - th ro u g h s im u la tio n s (a lre a d y a 4 0 y e a r e ffo rt ; e x tre m e ly c o m p le x & e x p e n s ive 6 D ra d ia tio n -h y d ro d y n a m ic s p ro b le m re q u irin g ~ o p e ra tio n s / s im u la tio n or ~1 C P U -y 3 0 T e ra flo p / s im u la tio n )

37 Looking into the heart of a core collapse supernova - through observations of neutrinos (up to now only SN1987A) - through observations of gravitational waves (not yet occured! Would provide kind of Rosetta stone!) - th ro u g h s im u la tio n s (a lre a d y a 4 0 y e a r e ffo rt ; e x tre m e ly c o m p le x & e x p e n s ive 6 D ra d ia tio n -h y d ro d y n a m ic s p ro b le m re q u irin g ~ o p e ra tio n s / s im u la tio n or ~1 C P U -y 3 0 T e ra flo p / s im u la tio n )

38 Looking into the heart of a core collapse supernova - through observations of neutrinos (up to now only SN1987A) - through observations of gravitational waves (not yet occured! Would provide kind of Rosetta stone!) - through simulations (already a 40 year effort ; extremely complex & expensive 6D radiation-hydrodynamics problem requiring ~1021 operations / simulation or 30 Teraflop / simulation)

39 Gravitational radiation - ripples in the fabric of spacetime (relative to smooth background) - far from strong gravitational fields (weak gravitation) g = + h h 1 Minkowski metric + small perturbation - plug into Einstein field equations --> wave equation ht Tjk = 0 ( ht Tjk is analogue of vector potential Ai in electrodynamics )

40 Gravitational radiation - leading-order EM multipole radiation from a non-relativistic charge distribution is dipole radiation 1 r A j t, x = d j t cr c (Lorentz-gauge vector potential in wave zone; r x ; dj: electric dipole moment) - leading-order GW multipole radiation from a mass-energy distribution is quadrupole radiation 2 G TT r h t, x = 4 Q jk t rc c TT jk (transverse-traceless-gauge; Qjk: mass quadrupole moment)

41 Einstein quadrupole formula (valid for slow motion v«c and weak fields Rs v 2G 1 h jk = 4 Q jk ~ R c c R «c2) 2 Q ~MR 2 /T2 ~Mv 2 Rs=1 km, v/c=0.1, R=10kpc ---> h ~ GW luminosity 2 d EGW 1 G RS 2 jk ~ LGW= = 5 Q dt 5c R v c 6