Supernova Explosions and Remnants Stellar Structure

Supernova Explosions and Remnants stellar structure

For a 25 solar mass star, the duration of each stage is stellar corpses: the core

When the central iron core continues to grow and approaches Mch , two processes begin: nuclear photodisintegration and neutronization.

Nuclear photodisintegration: The temperature is high enough for energetic photons to be abundant and get absorbed in the endothermic reaction:

with an energy consumption of 124 MeV. The Helium nuclei are further unbound:

consuming 28.3 MeV(the binding energy of a He nucleus). The total energy of the star is reduced per nucleon by

With about 10 57 protons in a Chandrasekhar mass, this corresponds to a total energy loss of stellar corpses: the core

Neutronization: The large densities in the core lead to a large increase in the rates of processes such as

This neutronization depletes the core of electrons and their supporting degeneracy pressure, as well as energy, which is carried off by neutrinos. The two processes lead, in principle, to an almost total loss of thermal pressure support and to an unrestrained collapse of the core of a star on a free-fall timescale:

In practice, at these high densities, the mean free path for neutrino scattering becomes of order the core radius. This slows down the energy loss, and hence the collapse time to a few seconds. core collapse supernovae

As the collapse proceeds and the density and the temperature increase, the reaction

becomes common, and is infrequently offset by

leading to a equilibrium ratio of densities

Thus most nucleons become neutrons review article

type Ia supernovae. If it were not for radioactive heating, adiabatic radius of ϳ109 km; however, it was dimmer than a typical type II expansion of the debris would cool it to near invisibility in less than and early relied on 56Ni to power its muted optical light curve. Yet an hour. Type Ia supernovae are about ten times less prevalent than there is no reason to suspect that the explosion itself was not of the core-collapse supernovae, but yield about ten times as much iron, common core-collapse variety. The light curve and spectrum of a are often more than ten times brighter at peak light, and are supernova reflect more its progenitor’s radius, chemical makeup, spectacular sources of nuclear g-ray lines and continuum8. It is and expansion velocities than the mechanism by which it exploded. with these bright supernovae that observers are now obtaining the To the theorist, the achievement of the critical Chandrasekhar mass best and, perhaps, the most provocative information about the unites the types; the supernova mechanism is either by implosion to geometry of the Universe. nuclear densities and subsequent hydrodynamic ejection, or by Astronomers use observational, not theoretical, criteria to type thermonuclear runaway and explosive incineration. supernovae. A type I supernova (such as a type Ia) is one with no There is approximately one supernova explosion in the Universe hydrogen in its spectrum, while the spectrum of a type II supernova every second. In our galaxy, there is one supernova every ϳ30–50 has prominent hydrogen lines. The epochal supernova in the Large years and one type Ia supernova every ϳ300 years. Supernova Magellanic Cloud (LMC), SN1987A, was a core-collapse supernova, hunters, peering deeply with only modest-aperture telescopes, can because it exploded as a ϳ15–20M᭪ blue supergiant with a radius of now capture a dozen or so extragalactic supernovae per night, ϳ4 ϫ 107 km (ref. 9) and not as the canonical red supergiant with a mostly the bright type Ias. Approximately 200 supernova remnant shells are known in the Milky Way and these are radio, optical, and X-ray echoes of only the most recent galactic supernova explosions. review article Within the last millennium, humans have witnessed and recorded six supernovae in our galaxy (Table 1). nito oge r St 9 type Ia supernovae. If it were not for radioactive heating, adiabatPicr radiusaor f ϳ10 km; however, it was dimmer than a typical type II expansion of the debris would cool it to near invisibility in less than and early relied on 56Ni to power itsSmuupteedrnoopvtiaceal flrigohmt cmuraves.sYievte stars an hour. Type Ia supernovae are about ten times less prevalent than there is no reason to suspect that theAexsptlaors’isonfiirtsstelfthwearsmnootnoufctlheear stage is the fusion of hydrogen into core-collapse supernovae, but yield about ten times a8s much ironH, FceomO m- Soi n core-collapse variety. The light curve and spectrum of a 6x10 km He helium in its hot core. With the exhaustion of core hydrogen, most are often more than ten times brighter at peak light, and are supernova reflect more its progenitostra’srsratdhiuesn, cphreomcieceadl mtoakesuhpe,ll hydrogen burning, and then to core spectacular sources of nuclear g-ray lines and continuum8. It is and expansion velocities than the mechanism by which it exploded. with these bright supernovae that observers are now obtaining the To the theorist, the achievement of thheecliruitmicalbCuhrannindrga.seTkhhearamshaess of the latter are predominantly carbon best and, perhaps, the most provocative information about the unites the types; the supernova mechanidsmoxisyegitehnerabnydimlopwlo-smionastso stars do not proceed beyond this stage. C geometry of the Universe. Ironnuocrleear densities and subsequent hHydorwodeyvnear,msticaresjewctiitohnm, oarssbeys from ϳ8M᭪ to ϳ60–100M᭪ (the upper review article Astronomers use observational, not theoretical, criteria to type thermonuclear runaway and explosivlieminitcidneepraetniodni.ng upon the heavy-element fraction at birth) proceed supernovae. A type I supernova (such as a type Ia) is one with no There is approximately one supernova explosion in the Universe 3 to carbon burning, with mostly oxygen, neon, and magnesium as hydrogen in its spectrum, while the spectrum of a typ6xe1I0I skumpernova every second. In our galaxy, there is one s1u,2pernova every ϳ30–50 9 ashes . For stars more massive than ϳ9–10M᭪, the ashes of carbon type Ia supernovae. If it were not for rhaadsiporaocmtiivneenhtehaytdinrogg,eandliianbesa.tTiche eproadchiualssuopfeϳrn1o0va kinmth; ehLoawrgeever,yietarws aasndimonme etryptehaIan sauptyerpniocaval teyvpeeryIIϳ300 years. Supernova 56 burning achieve sufficient temperatures to ignite and they burn expansion of the debris would cool it tMo angeeallraninicvCisliobuildit(yLMinCl)e,sSsNth19a8n7A, wanasdaecaorrley-croellaiepdseosunperNnoivtao, pohwunerteirtss, pmeeurtinedg doepetpilcyawl iltihghotnclyumrvoed.eYset-taperture telescopes, can predominantly to silicon, sulphur, calcium, and argon. Finally, these an hour. Type Ia supernovae are aboutbteecnautsiemiteesxlpelsosdpedreavsaalϳen1t5t–h2a0nM᭪ btlhuerseupiserngioanrtewasiothnatroadsiuuspoefct tnhoawt tchaepteuxrpe loa sdioonzenitsoerlf swoaesxntroatgaolafctthice supernovae per night, 7 ~ products ignite to produce iron and its congener isotopes near the core-collapse supernovae, but yield abϳo4uϫt t1e0n ktimm(ersefa.s9)manudchnoitroasnt,he cacnoomnimcaol nredcosurpe-ecrgoilalnatpwseithvaariet1 my.oTsthlyethliegbhrtigchutrtvyepeanIads. sAppepcrtorxuimatoeflya200 supernova remnant

s Collapse of Core e peak of the nuclear binding energy curve. Fusion is exothermic only c shells(~1a.r5eMkn) own in the Milky Way and these are radio, optical, and are often more than ten times brighter at peak light, and are supernova reflect more its p. rogenitor’s radius, chemical makeup, spectacular sources of nuclear g-ray lines and continuum8. It is and expansion velocities thanXt-hreaymecehcoheasnoifsomnlbyythwehmicohst irteceexnptlfgooadrlaetcdhti.ec sauspsermnobvlayeoxfplloigsihotnesr. elements into elements up to the iron SuWpeirtnhin the last millennium, humansgrhoauvep,wnitonetsbseedyoanndd.reHcoerndcede, at the end of a massive star’s thermo- with these bright supernovae that observers are now obtaining the To the theorist, the achievrleyment oovf the critical Chandrasekhar mass Ea a 00 kmsi/xs supernovae in our galaxy (Table 1). ,0 Bo nuclear life, it has an ‘onion-skin’ structure in which an iron or best and, perhaps, the most provocative information about the guennitiotreSs the types; the supe60rnova meuchanism is either by implosion to o t a - n Pr r c 0 e oxygen–neon–magnesium core is nested within shells comprised of 0 geometry of the Universe. nuclear densities and0 subseqSuupenertnohS vyaderofrdoymnammasicsiveejescttaiorsn, or by , 3 h 0 o elements of progressively lower atomic weight at progressively 2x10 km 3 Astronomers use observational, not theoretical, criteria to type thermonuclear runaway and Aexsptlaor’ssivc fiersitntchienremraotniuocnle.ar stage is the fusion of hydrogen into 8 H Fe O - Si k supernovae. A type I supernova (such as a type Ia) is o6xn1e0 wkmith no He There is approximately onehesluiupmerinnoivtsaheoxtpcloorsei.oWnitihntthheeexUhnaluiovswetireosrne odfecnosrietiheysdraongedn,tmemospt eratures. The outer zone consists of hydrogen in its spectrum, while the spectrum of a type II supernova every second. In our galaxy, tshtaerrsethisenonperoscuepedertnoosvhaelelvheyrdyroϳge3un0n–b5uu0rrnninedg, haynddrothgeenntoancdor‘eprimordial’ helium. A typical nesting is has prominent hydrogen lines. The epochal supernova in the Large years and one type Ia supehrneloiuvma beuvrenriyng. T3h0e0asyheeasros.f tShueplaetFrtneroavraeSipredoOminaHntely carHbo. nThe oxygen in the ‘oxygen’ zone is the ν ν ϳ → → → → M and oxygen and low-mass stars do nmotajporrocseoeudrbceyoofnodxtyhgisenstaigne.the Universe, for little oxygen survives in Magellanic Cloud (LMC), SN1987A, was a core-collapse supernova, hnuCno ters, peering deeply with only modest-aperture telescopes, can Iro re ν Howeverν, stars with masses from ϳ8Mth᭪eteojeϳc6ta0–o1f0t0hMe ᭪ra(rthere utypppeerIa supernovae. These shells are not pure, because it exploded as a ϳ15–20M᭪ bluecoresupergian tcollapsewith a radius of supernovaenow capture a dozen or solimexitrdaegpaeMlnadcitnicg uspuopnerthneohveaaevyp-elremneingthftr,action at birth) proceed 7 Hot, e xtended ϳ4 ϫ 10 km (ref. 9) and not as the canonical red supergiant 3with a mostly the bright tνype Ias. Amanpttolepcraorxbiomnabtνeulryni2n0g0, wsuithpemrnoostvlya orxeymgenna,nnteon, and magnesium as 6x10 km DENSE 1,2 shells are kn2 own in the MilkyasWheasy a. nFodrtshtaerssemaorreermadasisoi,veotphtaincaϳl,9a–n1d0M᭪, the ashes of carbon 2x10 km M C ORE X-ray echoes of onνly the mostbruercneinngt gaachlνaiecvteicssuuffipceirennot vteamepxeprlaotsuiroens st.o ignite and they burn predominantly to silicon, sulphur, caTlcaiubmle, a1ndSuaprgeorn.oFvianealtlyh,atthehsaeve exploded in our Galaxy and the Large Within the last millennium, humans Mhave witnessed and recMoradgedllanic Cloud within the last millennium

~ ν products ignite to produce iron and its congener isotopes near the si1 x supernovae in our galaxy (Table 1ν ). s Collapse of Core e peak of the nuclear binding energy cuSupernovarve. Fusion is exothermYearic o(ADn)ly Distance (kpc) Peak visual magnitude enitor c (~1.5 M ) ν ν g S . ro t a Ea r ...... P r rly for the taassembly of lighter elements into elements up to the iron Prot ron S SN1006 1006 2.0 −9.0 Suup pernovae from massiveonsetuat rs ly S erno group, not beyond. Hence, at the end of a massive star’s thermo- ar v ~ Crab 1054 2.2 −4.0 E km/ a 0 0 s . ,00 A stBar’s ﬁrst thermonuclear n1 sutacgleearislifteh, eit fhuassioann ‘oofnihoynd-srkoing’ensSN1181triuncttoure in which an ir1181on or 8.0 ? 0 o - 8 Fe u 1

H O - Si 6 n - s c 6x10 km He 0 e e RX J0852-4642 ϳ1300 ϳ0.2 ?

helium in its hot core. With toc hxeygeexnh–anuesotino–nmoafgnceosriuemhycdoreoigsenne,stmedowstithin shells comprised of 0 0 S , 3 h Tycho 1572 7.0 4.0 0 − o elements of progressively lower atomic weight at progressively 2x10 km 3

stars thc en proceed to shell hydrogen burning, and then to core k lower densities and temperatures.KeplerThe outer zone consi1604sts of 10.0 −3.0 helium burning. The ashes of the latter are predominantly cCasarbAon ϳ1680 3.4 ϳ6.0? unburned hydrogen and ‘primordial’ helium. A typical nesting is and oxygen and lo3w0 k-mmass sDtEaNrSEs do not proceed beyond thisSN1987Astage. 1987 50 Ϯ 5 3.0 C OFReE Si O He H. The oxyge..n.....i..n.....t..h...e.....‘.o...x..y...g..e...n...’...z...o...n...e....i..s....t..h...e...... ron Core ν Howν ever, stars with maL sses from→ϳ8M→᭪ to→ϳ60→–100M᭪ (the Theseuppe‘historical’r supernovae are only a fraction of the total, because the majority were shrouded I M a r t major soa urce of oxygen in the Universe, for little oxygen survives in e t from view by the dust that pervades the Milky Way. Thus, it is estimated that this historical cohort ν limit deνpending upon the heavy-eleS ment fraction at birth) proceed P r the ejnecta of the rarer type Ia supernorepresentsvae. Theonlyse sabouthells 20%are nofothet pugalacticre, supernovae that exploded since AD1000. Included are M ot oneutro 3 Hot,teoxtendcedarbon burning, with mostly oxygen, neon, and magnesiuSN1987A,m as which exploded not in the Milky Way but in the Large Magellanic Cloud (one of its 6x10 km ν mantle 1,2 ν nearby satellite galaxies), RX J0852-4642 (ref. 77, ref. 11), a supernova remnant whose recent 2 aDsENhSEes . For stars more massive than 9–10M , the ashes of carbon ϳ ᭪ (ϳAD1300) and very nearby birth went unrecorded, perhaps because it resides in the Southern 2x10 km FMigure 1 TheCsOeREquence of events in the collapse of a stellar core to a nascent neutron star. ν burning aνchieve sufﬁcient temperatures to ignite and theyHemisphereburn (but in fact for reasons that are as yet unknown), and Cas A, a supernova remnant that It begins with a massive star with an ‘onion-skin’ strTucatbulree,1goSeusptherronuogvhaewhtihtea-tdwhaavrfecoerxeplodewasd ibornn ouinr historicalGalaxy times,and tbuthe whoseLargeﬁery birth was accompanied by a muted visual display that M predominantly to silicon, sulpMhaugre,llcaanilcciCulomud, awnitdhinarthgeolnas.tFminillaelnlnyimay,utmhehavese been recorded only in the ambiguous notes of the seventeenth-century astronomer John imploνsion, to core bouνnce and shock-wave formation, to the protoneutron-star stage

~ products ignite to produce iron and its congener isotopes neFlamsteedar the (ref. 78). The distances and peak visual magnitudes quoted are guesses at best, except

1 Supernova Year (AD) Distance (kpc) Peak visual magnitude ν ν s Collapse of Core befEore explosion, and ﬁnally to the cooling and iso.l..a..t..e..d...-..n...e...u...t.r..o...n..-...s..t..a..r....s..t..a...g..e.....a..f..t..e..r...... for...... SN1987A...... Astronomical...... magnitudes...... are logarithmic and are given by the formula M V ¼ e ar peak of tahr e nuclear binding energy curve. Fusion is exothermic only c (~1.5 M ) ly P S t SN1006 1006 Ϫ2.02:5log ðbrightnessÞ þ constant.9.0 Hence, every factor of ten increase in brightness represents a . rot oneutron 10 − explosion. This ﬁgure is not to scale. The wavy arrows depict escaping neutrinos and the decrease in magnitude by 2.5. For comparison, the Moon is near 12 magnitudes, Venus at peak is

fo~ r the assembly of lighter elCrabements into eleme1054nts up to the2.2iron −4.0 −

0 . 1 SN1181 1181 4.48.0 magnitudes, and good?eyes can see down to about +6 magnitudes. straight arrow- s depict mass motion. − Supe 1 y rn grs oup, not beyond. Hence, at the end of a massive star’s thermo- rl o e RX J0852-4642 ϳ1300 ϳ0.2 ?

v c Ea a 00 km/s Tycho 1572 7.0 4.0 ,0 Bo nuclear life, it has an ‘onion-skin’ structure in which an iron or − 60 u - n Kepler 1604 10.0 −3.0 c 728 © 2000 Macmillan Magazines Ltd NATURE | VOL 403 | 17 FEBRUARY 2000 | www.nature.com 0 e oxygen–neon–magnesium core is nested within shells comprised of 0 Cas A ϳ1680 3.4 ϳ6.0? 0 S , 3 h DEN 0 SE SN1987A 1987 50 Ϯ 5 3.0 o 30 km elements of progressively lower atomic weight at progressively 2x10 km 3

c C ORE ...... k L These ‘historical’ supernovae are only a fraction of the total, because the majority were shrouded a lower dr ensities and temperatures. The outer zone consists of t a e t from view by the dust that pervades the Milky Way. Thus, it is estimated that this historical cohort S P unburned hydrogen and ‘prirepresentsmordiaonlyl’ habouteliu20%m.of Athe tgalacticypicasupernovael nestinthatg explodedis since AD1000. Included are rot ro n oneut SN1987A, which exploded not in the Milky Way but in the Large Magellanic Cloud (one of its Fe Si O He H. Thnearbye oxsatelliteygen galaxies),in theRX‘oJ0852-4642xygen’ (ref.zo77,neref.is11),thaesupernova remnant whose recent ν ν → → → → M major source of oxygen in the(ϳUAD1300)niveandrsevery, fonearbyr littbirthle owentxygunrecorded,en surviperhapsves inbecause it resides in the Southern Figure 1 The sequence of events in the collapse of a stellar core to a nascent neutron star. Hemisphere (but in fact for reasons that are as yet unknown), and Cas A, a supernova remnant that ν ν It begins with a massive star with an ‘onion-skin’ sttrhucetuerej,egcoteas tohrfoutghhewhriater-edwratrfycporee Ia wassupbornerninohistoricalvae. Ttimes,hesbute swhosehellsfieryarbirthe nwasot accompaniedpure, by a muted visual display that M may have been recorded only in the ambiguous notes of the seventeenth-century astronomer John Hot, eixmtenpdleodsion, to core bounce and shock-wave formation, to the protoneutron-star stage Flamsteed (ref. 78). The distances and peak visual magnitudes quoted are guesses at best, except ν mantle ν before explosion, and finally to the cooling and isolated-neutron-star stage after for SN1987A. Astronomical magnitudes are logarithmic and are given by the formula M V ¼ 2 DENSE Ϫ 2:5log10 ðbrightnessÞ þ constant. Hence, every factor of ten increase in brightness represents a 2x10 km M CeOxplosion. This figure is not to scale. The wavy arrows depict escaping neutrinos and the RE decrease in magnitude by 2.5. For comparison, the Moon is near −12 magnitudes, Venus at peak is ν straight arrows dνepict mass motion. −4.4 magnitudes, and good eyes can see down to about +6 magnitudes. Table 1 Supernovae that have exploded in our Galaxy and the Large M Magellanic Cloud within the last millennium ν 728 ν © 2000 Macmillan Magazines Ltd NATURE | VOL 403 | 17 FEBRUARY 2000 | www.nature.com Supernova Year (AD) Distance (kpc) Peak visual magnitude E ν ν ...... ar ar ly S t Prot oneutron SN1006 1006 2.0 −9.0

~ Crab 1054 2.2 −4.0

0 .

1 SN1181 1181 8.0 ?

1 s

e RX J0852-4642 ϳ1300 ϳ0.2 ? c Tycho 1572 7.0 −4.0 Kepler 1604 10.0 −3.0 Cas A ϳ1680 3.4 ϳ6.0? 30 km DENSE SN1987A 1987 50 Ϯ 5 3.0 C ORE ...... L These ‘historical’ supernovae are only a fraction of the total, because the majority were shrouded a r t a e t from view by the dust that pervades the Milky Way. Thus, it is estimated that this historical cohort S P represents only about 20% of the galactic supernovae that exploded since AD1000. Included are rot ro n oneut SN1987A, which exploded not in the Milky Way but in the Large Magellanic Cloud (one of its nearby satellite galaxies), RX J0852-4642 (ref. 77, ref. 11), a supernova remnant whose recent (ϳAD1300) and very nearby birth went unrecorded, perhaps because it resides in the Southern Figure 1 The sequence of events in the collapse of a stellar core to a nascent neutron star. Hemisphere (but in fact for reasons that are as yet unknown), and Cas A, a supernova remnant that It begins with a massive star with an ‘onion-skin’ structure, goes through white-dwarf core was born in historical times, but whose fiery birth was accompanied by a muted visual display that may have been recorded only in the ambiguous notes of the seventeenth-century astronomer John implosion, to core bounce and shock-wave formation, to the protoneutron-star stage Flamsteed (ref. 78). The distances and peak visual magnitudes quoted are guesses at best, except before explosion, and finally to the cooling and isolated-neutron-star stage after for SN1987A. Astronomical magnitudes are logarithmic and are given by the formula M V ¼ Ϫ 2:5log ðbrightnessÞ þ constant. Hence, every factor of ten increase in brightness represents a explosion. This figure is not to scale. The wavy arrows depict escaping neutrinos and the 10 decrease in magnitude by 2.5. For comparison, the Moon is near −12 magnitudes, Venus at peak is straight arrows depict mass motion. −4.4 magnitudes, and good eyes can see down to about +6 magnitudes.

728 © 2000 Macmillan Magazines Ltd NATURE | VOL 403 | 17 FEBRUARY 2000 | www.nature.com core collapse supernovae review article type Ia supernovae. If it were not for radioactive heating, adiabatic radius of ϳ109 km; however, it was dimmer than a typical type II expansion of the debris would cool it to near invisibility in less than and early relied on 56Ni to power its muted optical light curve. Yet an hour. Type Ia supernovae are about ten times less prevalent than there is no reason to suspect that the explosion itself was not of the core-collapse supernovae, but yield about ten times as much iron, common core-collapse variety. The light curve and spectrum of a are often more than ten times brighter at peak light, and are supernova reﬂect more its progenitor’s radius, chemical makeup, spectacular sources of nuclear g-ray lines and continuum8. It is and expansion velocities than the mechanism by which it exploded. with these bright supernovae that observers are now obtaining the To the theorist, the achievement of the critical Chandrasekhar mass best and, perhaps, the most provocative information about the unites the types; the supernova mechanism is either by implosion to geometry of the Universe. nuclear densities and subsequent hydrodynamic ejection, or by Astronomers use observational, not theoretical, criteria to type thermonuclear runaway and explosive incineration. supernovae. A type I supernova (such as a type Ia) is one with no There is approximately one supernova explosion in the Universe hydrogen in its spectrum, while the spectrum of a type II supernova every second. In our galaxy, there is one supernova every ϳ30–50 has prominent hydrogen lines. The epochal supernova in the Large years and one type Ia supernova every ϳ300 years. Supernova Magellanic Cloud (LMC), SN1987A, was a core-collapse supernova, hunters, peering deeply with only modest-aperture telescopes, can because it exploded as a ϳ15–20M᭪ blue supergiant with a radius of now capture a dozen or so extragalactic supernovae per night, ϳ4 ϫ 107 km (ref. 9) and not as the canonical red supergiant with a mostly the bright type Ias. Approximately 200 supernova remnant shells are known in the Milky Way and these are radio, optical, and X-ray echoes of only the most recent galactic supernova explosions. Within the last millennium, humans have witnessed and recorded six supernovae in our galaxy (Table 1). nito oge r St Pr ar Supernovae from massive stars A star’s ﬁrst thermonuclear stage is the fusion of hydrogen into 8 H Fe O - Si 6x10 km He helium in its hot core. With the exhaustion of core hydrogen, most stars then proceed to shell hydrogen burning, and then to core helium burning. The ashes of the latter are predominantly carbon and oxygen and low-mass stars do not proceed beyond this stage. C Iron ore However, stars with masses from ϳ8M᭪ to ϳ60–100M᭪ (the upper limit depending upon the heavy-element fraction at birth) proceed

3 to carbon burning, with mostly oxygen, neon, and magnesium as 6x10 km 1,2 sn 1987a ashes . For stars more massive than ϳ9–10M᭪, the ashes of carbon burning achieve sufﬁcient temperatures to ignite and they burn predominantly to silicon, sulphur, calcium, and argon. Finally, these

~ products ignite to produce iron and its congener isotopes near the 1 s Collapse of Core e peak of the nuclear binding energy curve. Fusion is exothermic only c (~1.5 M ) . for the assembly of lighter elements into elements up to the iron Supern group, not beyond. Hence, at the end of a massive star’s thermo- rly ov Ea a 00 km/s ,0 Bo nuclear life, it has an ‘onion-skin’ structure in which an iron or 60 u - n c 0 e oxygen–neon–magnesium core is nested within shells comprised of 0 0 S , 3 h 0 o elements of progressively lower atomic weight at progressively

2x10 km 3 c k lower densities and temperatures. The outer zone consists of unburned hydrogen and ‘primordial’ helium. A typical nesting is Fe Si O He H. The oxygen in the ‘oxygen’ zone is the ν ν → → → → M major source of oxygen in the Universe, for little oxygen survives in ν ν the ejecta of the rarer type Ia supernovae. These shells are not pure, M Hot, e xtended ν mantle ν 2 DENSE 2x10 km M C ORE ν ν Table 1 Supernovae that have exploded in our Galaxy and the Large M Magellanic Cloud within the last millennium ν ν Supernova Year (AD) Distance (kpc) Peak visual magnitude E ν ν ...... ar ar ly S t Prot oneutron SN1006 1006 2.0 −9.0

~ Crab 1054 2.2 −4.0

0 .

1 SN1181 1181 8.0 ?

1 s

728 © 2000 Macmillan Magazines Ltd NATURE | VOL 403 | 17 FEBRUARY 2000 | www.nature.com sn 1987a: neutinos Dead Stars and Black Holes a.k.a. Astronomy 15 Winter Quarter 2008 stellarGravit ycorpses:Triumphan neutront: Key Co ncestarspts

The energy of formation of a neutron star is largely determined by the change in the gravitational binding caused by core-collapse. Just before collapse we have a core with mass comparable to the sun and radius of about 1000km. After the ET = EK + Ug (1) collapse we have a neutron star with a similar mass but with a radius of about 10 km:

2 2 GM 46 MNS 10 km Ug = 3 10 J (2) ⇤ R ⇥ M RNS ⇥ ⇥

3 B = G (3) 5 AM 5/3 E = (4) K R2

MOV = 1.5 2.5M (5)

MOV = 4MC (6)

R M 1/3 NS = 0.00001 NS (7) R M ⇥

1 GMm mv2 + = 0 + 0 (8) 2 esc r 2GM v = c = (9) esc R ⇤ S neutron star kicks! core collapse supernovae supernova remnants supernova remnants

As it propagates, a SNR causes a strong shock to occur since the ejecta is moving highly supersonically compared to the surrounding mass supernova remnants

Detection of 1keV photons from SNRs suggest:

10 pc How much energy does it take to ionize this much gas?

where does the energy comes from?

but the sound speed supernova remnants