Supernova Remnants (SNRs) Seminars on X-ray Astronomy Physics 8.971 November 1, 2007 Claude R. Canizares The remnants of supernovae are THE major sources of chemical enrichment in the universe and significant sources of energy in galaxies Supernovae also produce all the stellar-mass compact objects (neutron stars & black holes) http://imagine.gsfc.nasa.gov/docs/science/know_l1/supernovae.html And, they are beautiful to look at! Chandra X-ray image of Cas A Credit: NASA/CXC/MIT/UMass Amherst/M.D.Stage et al. Some facts about Supernovae and Supernova Remnants • ~ 1 supernova explodes every 30-50 years in our Galaxy • ~ 1 supernova explosion occurs every second somewhere in the universe • Remnants of supernovae are visible for up to 100,000 yrs (primarily in radio and X-ray bands) • Roughly ~200 SNRs identified in our Galaxy • ~100,000,000 supernovae in Galaxy’s history • Supernovae are sources of – Most heavy element enrichment of the universe – Heating of galaxy interstellar medium – Many (most) cosmic rays – All neutron stars and stellar-mass black holes – Triggered star formation e.g. see Burrows, 2000 Nature 403, 727 Supernova Explosions • Triggered by the collapse of ~ Msun object, either • degenerate Fe-rich core of a massive (>8 Msun) YOUNG star • “core collapse” supernova • bounce ejects most of the mass • forms neutron star or black hole • accreting C-O white dwarf in binary system (OLD star) • massive thermonuclear “deflagration” (“slow” explosion) • total “incineration” of star with no remnant • Classified in two “types” based on optical spectrum • Type 1 - No hydrogen lines --> Absence of H-rich outer layers in progenitor star • Type 1a -- accreting WD progenitor • Type 1b -- core progenitor that lost it’s outer envelope • Type 2 - Yes hydrogen lines --> core collapse Gravitational energy released during core collapse: GM 2 GM 2 GM 2 E " # " ,R2 << R1 R1 R2 R2 33 M " Msun = 2x10 gm R "10km =105cm $ E ~ 1053erg U.C. Berkeley This is 1000x what the sun would radiate over the entire ! age of the universe! Most energy comes out as neutrinos, but ~10% percent 9 emerges as kinetic energy of ejecta: ~10-20 Msun x (10 cm s-1) => 1052 erg Type 2, core collapse supernova Core collapses, bounces, emits huge neutrino pulse Layers from Si shell outward ejected at 5,000-10,000 km s-1 providing most of the heavy elements in the universe Type 1a supernova: a “standard candle” Relatively ~uniform conditions make this as close to a universal “standard candle” as we have in cosmology. Used to measure the acceleration of the universe! http://csep10.phys.utk.edu/astr162/lect/supernovae/type1.html Three Phases of SNR Evolution 1. “Free” Expansion Phase • Mass of ejecta >> Swept-up mass • Energy losses are negligible • Lasts few hundreds to thousands yrs 2. Adiabatic Phase • Swept up mass dominates • Energy losses still small • Lasts tens of thousands of yrs 3. Radiative Phase • Radiative losses important Eventually SNR dissipates, mixes and merges with interstellar medium Shock-heating of circum-stellar material Expanding stellar ejecta is like a piston moving at supersonic velocities 1/2 e.g. v >> vsound~ (kT/mp) www.eng.vt.edu Supersonic shock front vsound vplane >> vsound www.lightandmatter.com/.../ 3vw/ch03/ch03.html Physics of a strong shocks (highly supersonic) “piston” shocked gas shock front unshocked gas "s,vs,Ts "0,v0,T0 vshock >> vsound ; need only use conservation of energy, momentum (pressure equilibrium) and mass flow to derive “jump” conditions across shock front " v = " v Mass conservation ! o o s s ! 2 2 P0 + "0v0 = Ps + "svs Momentum/pressure conservation 1 2 5 1 2 5 2 v0 + 3 P0 = 2 vs + 3 Ps Energy conservation ! (e.g. see McKee & Hollenback 1980 Ann Rev Astron Ap 18, 219) Physics of a strong shocks (highly supersonic) Analyze in frame moving with shock front “piston” shocked gas shock front unshocked gas “flowing” toward shock front "0,v0,T0 vshock >> vsound ; need only use conservation of energy, momentum and mass flow to derive “jump” conditions across shock front " v = " v Mass conservation o o s s ! 2 2 P0 + "0v0 = Ps + "svs Momentum/pressure conservation 1 2 5 1 2 5 2 v0 + 3 P0 = 2 vs + 3 Ps Energy conservation -1 then (for perfect gas) For vs ~ 1-5000 kms T ~ 107 - 108 K "s = 4"0 s ! 3 2 => X-rays dominate! kTs = 16 µvs , where µ = mean particle mass (e.g. see McKee & Hollenback 1980 Ann Rev Astron Ap 18, 219) ! Deceleration of ejecta drives a second shock “backwards” heating the ejecta (“reverse shock” in the moving frame) “gaseous piston” “reverse” shock front primary shock front unshocked gas Shocked stellar ejecta: Shocked circum-stellar matter: cooler, denser, hotter, less dense rich in heavy elements Shocks in ionized gas with magnetic fields also accelerate protons and and electrons to relativistic energies giving synchrotron radiation and “cosmic rays” (high energy particles) Tycho’s SNR (1572) Colors related to temperature and composition PrimaryShock front (hottest region) Mix of circumstellar matter and stellar ejecta heated by “reverse shock” Distance ~2.4 kpc Dia ~ 8.5 arcmin ~ 6 pc = 2 1019 cm Mean expansion velocity ~ 7700 km s-1 Mass ~few Msun Mean density ~few particles cm-2 SN observed in 1572, probably Type 1a, no collapsed remnant has been seen X-ray Image: Chandra Observatory Cas A: Remnant of core collapse (Type 2 or 1b) SN shock Primary ~25 Msun Rich in Heavy Elements Dist: 3 kpc Age: ~300 yr Dia: 5’ = 5 pc Ejecta heated Colors related to by “reverse” temperature and shhock composition Cas A Collapsed stellar Remnant (Neutron star or Black Hole?) Chandra X-ray spectrum of Cas A Hwang et al. 2000 ApJ An Older Core Collapse SNR SNR E 0102-72 Dist = 60 kpc (in SMC) Age ~ 1000 yr; Dia ~ 10pc; M ~ 15-25 Msun Chandra Grating Spectrometer of SNR E0102-72 Flanagan et al. 2004 E0102-72 O VIII (O+7) Ly α E0102-72 O VII O VIII (O+6) (O+7) More ionized atoms on outside: evidence for “reverse” shock propagating into expanding ejecta Flanagan et al. 2004 Doppler Shifts 1800 kms-1 900 kms-1 -900 kms-1 -1800 kms-1 Flanagan et al. 2004 Pulsar-powered SNRs • Young core-collapse SNRs with active radio and/or X-ray pulsar at center • Relativistic particles and waves dominate emission (synchrotron) from radio to X-ray • Called “plerions” or center-filled SNRs (vs. “shell” SNRs) [Greek: pleres = “full”] The Crab Nebula Optical SN 1054 Crab Pulsar: 33 msec period Dist ~ 3 kpc Dia ~ 5 arcmin ~ 3 pc Crab Nebula & Pulsar X-ray pulsar Optical (Credits: X-ray: NASA/CXC/ASU/J. Hester et al.; Optical: NASA/HST/ASU/J. Hester et al.) Crab Nebula is powered by rotational energy I ~ Mr2 moment of inertia of neutron star 1 2 E = 2 I" rotational energy dE d" = I" energy loss dt dt for M = Msun,r =10 km, " = 2# /33 msec 1 d" and =10$11s$1 (observed slow down rate) " dt dE then ~ 1038erg s-1 or 100,000 x L dt sun vs. observed Crab luminosity = 5 1037 erg s-1 A cosmic, relativistic dynamo! ! SN1987A in the Large Magellanic Cloud Before After SN1987a ~20 years later Optical (Hubble) X-ray (Credit: X-ray: NASA/CXC/PSU/S.Park & D.Burrows.; Optical: NASA/STScI/CfA/P.Challis) Antenna Galaxy: Colliding galaxies trigger a “starburst” leading to thousands of supernovae Optical (stars) X-ray (hot, enriched gas) (Digitized Sky Survey) (Chandra: NASA,CXC, SAO) SNR G11.2-0.3 Thank you Questions? Credit: NASA/CXC/Eureka Scientific/M.Roberts et al..