Supernova Explosions and Remnants

Transcription

1 Supernova Explosions and Remnants

2 stellar structure For a 25 solar mass star, the duration of each stage is

3 stellar corpses: the core When the central iron core continues to grow and approaches M, two ch 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 energy loss of 57 protons in a Chandrasekhar mass, this corresponds to a total

4 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.

5 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

6 hydrogen lines. The epochal supernova in the Large ud (LMC), SN1987A, was a core-collapse supernova, ded as a!15 20M! blue supergiant with a radius of ref. 9) and not as the canonical red supergiant with a helium burning. The as years and one type Ia supernova every!300 y oxygen and low-ma and M hunters, peering deeply with However, only modest-apertur C n o stars with mas r o e Ir now capture a dozen or solimit extragalactic supern M depending upon th Hot, e xtende d mostly the bright type Ias. Approximately 200 with sup mantle to carbon burning, 2 ashes. For these stars more m shells are known inm the MilkyDENSE Way1,2and are ra 2x10 km C ORE achieve sufficie X-ray echoes of only recent galactic super the mostburning predominantly silicon M Within the last millennium, humans have towitness products ignite to produ six Csupernovae in our galaxy (Table 1). ollapse of C ore core collapse supernovae 3 6x10 km Core 30,00 La Ir o n h o ck es 3 2x10 km te 3 2 2x10 km ~1 sec ,0 0 k m /s B a ou h o ck es 30,00 y S u p er n o v nc 3 6 C ollapse of C ore (~1.5 M ) DENSE C ORE ~0.1-1 sec rl Ea 2x10 km t on eutr M to carbon burning, with mostly oxygen, neon, an ashes1,2. For stars more massive than!9 10M!, th M Figure 1 Theburning sequence of events in sufficient the collapse oftemperatures a stellar core to a nascent ne achieve to ignit Table 1goes Supernovae that It begins withpredominantly a massive Mstar with to an onion-skin structure, through white-d silicon, sulphur, calcium, Magellanic Cloud and withinarg th implosion, toproducts core bounce and shock-wave formation, to the protoneutron-sta ignite to produce iron and its congener Supernova Year (A and finally to the cooling and isolated-neutron-star before explosion, stage af... Ea peak of the nuclear binding energy curve. Fusion is ar rly t Pr o t o n e u t r o n S SN explosion. This not to scale.ofthelighter wavy arrows depict escaping neutrino forfigure the isassembly elements into elemen Crab 105 straight arrows depict mass motion. SN group, not beyond. Hence, atrxthe end of a massi J !130 Tycho nuclear life, it has an onion-skin structure in157w Kepler oxygen neon magnesium core is nested within sh Cas A!168 SN1987A 198 elements of progressively lower atomic weight 30 km... Hot, e xtended mantle 6x10 km ar 0- O - Si Ea nc Fe Fe He H peak of the nuclear bind ar rly for the assembly of ligh Pr o t o n e u t r o n S t Supernovae from massive stars S u p er n o group, not beyond. Hen rly va a E 0 0A k m /sstar s first thermonuclear nuclear stage islife, theit fusion has an o Bo,0 u 60 oxygen neon magnesiu helium in its hot core. With the exhaustion of core elements ofburning, progressive stars then proceed to shell hydrogen a lower densities and te helium burning. The ashes of the latter are predo unburned hydrogen and DENSE and oxygen and low-mass stars do not proceed b 30 km C ORE Fe Si O He H However, stars with masses from!8 M! toof!60 1 major source oxygen M limit depending upon the fraction P r heavy-element of the rarer ty o the ejecta on (~1.5 M ) St nit or St ar ~0.1-1 sec 8 6x10 km ~1 sec. ge Pr o DENSE C ORE

7 core collapse supernovae

8 sn 1987a Table 1 Supernovae that have exploded in our Galaxy and the Large Magellanic Cloud within the last millennium Supernova Year (AD) Distance (kpc) Peak visual magnitude... SN Crab SN ? RX J ? Tycho Kepler Cas A ? SN1987A These historical supernovae are only a fraction of the total, because the majority were shrouded

9 sn 1987a: neutinos

10 stellar corpses: neutron stars 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 collapse we have a neutron star with a similar mass but with a radius of about 10 km: U g GM 2 R = 3 M NS 1046 M 2 10 km R NS J

11 neutron star kicks!

12 core collapse supernovae

13 supernova remnants

14 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

15 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

16 supernova remnants