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Stellar Collapse R STELLAR COLLAPSE R. Canal To cite this version: R. Canal. STELLAR COLLAPSE. Journal de Physique Colloques, 1980, 41 (C2), pp.C2-105-C2-110. 10.1051/jphyscol:1980218. jpa-00219810 HAL Id: jpa-00219810 https://hal.archives-ouvertes.fr/jpa-00219810 Submitted on 1 Jan 1980 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. JOURNAL DE PHYSIQUE Colloque C2, supplément au n° 3, Tome 41, mars 1980, page C2-105 STELLAR COLLAPSE R . Canal Depar-tamento de Fisica de la Tierra y del Cosmos Univevsidad de Barcelona Spain Résumé .- On considère le problème de l'effondrement des étoiles à la fin de leur évolution . Las étoiles à grande masse (M ~ 10 M„) vont vers leur effondrement ayant épuisé (dans leurs couches centrales au moins) leurs combustibles thermonu­ cléaires . L'explosion de leurs couches extérieures doit se produire par transfert de 1'énergie gravitationnelle du noyau . On examine les différents mécanismes qui ont été proposés, ainsi que les incertitudes qui s'y rattachent. Les étoiles aux masses plus petites (sauf celles qui finissent comme naines blanches) rencontrent des instabilités explosives par suite de la formation, dans leur intérieur, de noyauKdont la composante électronique est fortement dégénérée. Là, l'issue dépend de la compétition des captures électroniques avec les. réactions thermonucléaires . Les conditions les plus favorables à l'effondrement ont lieu dans les systèmes doubles. La solution du problème posé par l'effondrement des étoiles passe par une meilleure connaissance de l'équation d'état aux grandes densités, des taux des réactions nucléaires, de l'opacité de la matière aux neutrinos, des régimes de combustion, des séparations de phase, de l'évolution des étoiles isolées et de celle des systèmes doubles rapprochés . Stellar collapse is a physical process that r his means stars that form very massive he­ is expected to account for : lium cores following hydrogen burning and -Neutron star formation, which comprises encounter instability due to pair formation-, the coming into being of radio pulsars -*• + (single neutron stars, mainly) and of X-ray Y *• e + e pulsars and bursters (neutron stars in clo­ se binary systems) . leading to r E (-1IIL-E-) g < 4/3 just before -Supernovae . central oxygen ignition (Barkat, Rakavy, -The bulk of the nucleosynthesis in the Ga­ and Sack 1967 ; Fraley 1968) . Dynamical stu­ laxy . dies of this case (Arnett 1978a) give an im­ -The origin of the galactic cosmic rays. plosion-explosion behaviour, both with and Stellar collapse might also produce black without remnant left, depending on the assu­ holes, gravitational waves, and neutrino, med mass of the helium core . The relevance •y-ray, X-ray, UV and IR "supernovae" . In of this mass range is doubtful, however. most cases mass ejection is needed, in Dearborn (1977), extrapolating the observed addition to the collapse, to explain the main-sequence mass-loss rates, concludes observed objects and phenomena. Energy that the masses of such stars, if they are emission must always occur, since stellar formed at all, will be reduced below the li­ collapse means forming a more gravitational mit for the occurrence of pair instability, ly bound object from' a less bound one . already during hydrogen burning . r he dynamic We will review the different types of stars process of star formation itself can also which are collapse candidates, stressing set the maximum mass of a star around the unsolved problems concerning their ul­ 60 - 100 M@ (Larson and Starrfield 19-71) . timate fates . We consider first single b) Massive stars : stars . Later we will discuss the supplemen­ 8 + ( 2 to 3) M. < M< M . tary possibilities related with close bina­ ® ~ paxr ry evolution . Those stars are able to go through all the 1- Single stars . - thermonuclear burning stages, from hydrogen a) Very massive stars : to silicon burning . rhey develop the classi­ cal onionring structure (Arnett 1973), with M>M . - 100 + 30M.- ~ paxr - © succesive burning shells corresponding, from Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980218 JOURNAL DE PHYSIQUE the center outwards, to Si, 0, Ne, C, He, cussing in this same volume different as- and H . One must have in mind, however, that pects of the physics of the collapse of most calculations stalt from helium cores, massive stars, I will only briefly indicate neglecting the hydrogen envelopes .The the main steps leading to our present view treatment of convection is doubtful, as are of the situation. mass loss effects. Further uncertainties are Two energy sources are available for produ- associated with the Si burning phase (Arnett cing a "mass cut" and obtaining an explo- 1977a). Anyway, Fe-Kki cores developat the sion : the thermonuclear energy of the man- centers of such stars, with masses in the tle and the gravitational potential of the 2 Mg F hey are ne- core.The last gives rise, by core contrac- range 1 -2 Mg <- Mcore -< -5 arly isothermal, with temperatures tion, to neutrino emission, infall kinetic r % 5 x 10' OK, and are supported by the de- energy, increase of rotation and of the ma- generate pressure of highly relativistic gnetic fields. electrons, so r 2 4/3. Core contraction Compression and heating of the mantle was leads to electron captures and pressure de- first proposed by Hoyle and Fowler (1960) : crease. Rising temperature (due to compres- the explosive thermonuclear burning of this sion and to the captures) induces endoergic material would release enough energy to photodisintegration of the nuclei. Both pro- eject a fraction of it and the whole enve- cesses start dynamical collapse. lope. Hydrodynamic calculations by Colgate At first sight, pure collapse of the massive and White (1966) showed that the compres- stars would be a natural outcome of their sed material is in fact "swallowed" by the evolution, when in their cores there is no neutronized core .The same authors sugges- more nuclear potential energy 1eft.rhe pro- ted energy transport by the neutrinos pro- blem is that such stars should also explode duced in the accretion shock front, at the as supernovae, ejecting their mantles and boundary of the core, to the zone corres- envelopes and leaving condensed remnants ponding to their last mean free path before (neutron stars and perhaps, in some cases, escape -the "neutrino photospherew-, as an ejection mechanism. Later work concentrated black holes) . A few reasons for that are : -The existence of at least two associations on the problem of neutrino transport and its neutron star-supernova remnant (Crab and coupling with the hydrodynamics, both newto- Vela) .The Crab nebula is very helium-rich nian and general-relativistic (Arnett 1968 ; and its mass could be as high as 8 - 10 Ma. Wilson 1971) . Experimental results in 1973, -Cas A, a supernova remnant, shows evidence indicating the presence of a neutral current for nucleosynthesis of the heavy elements. in the weak interaction, opened up new pos- -The onion-ring structure developed by tho- sibilities for mass ejection during collapse se stars appears to be the ideal site for (see, Freedman, Schramm, and Tubbs 1977) . the synthesis of the heavy elements, both Coherent scattering by the heavy nuclei in explosively and non-explosively (Arnett and the outer core and in the mantle, of the neutrinos produced in the inner core, would Schramm 1973 ; Arnett 197833) . -For a 1.4M Fe-IS core collapsing to a neu- mainly transfer momentum to those layers and 0 tron star, the gravitational energy release perhaps reverse their motion. In addition to this, the change of r from is % 10~~er~.So, only about 1 % of this energy would suffice, if transferred to the lower to higher than 4/3, at or above nu- mantle and envelope, to blow them off with clear densities, was known to cause a "boun- energies typical for supernova events. ce" of the inner core and then a reflected -'Type 11 supernovae are concentrated to- shock wave. In this way, a fraction of the wards the spiral arms in spiral galaxies kinetic energy of the collapsing core can be (Maza and Van den Bergh 1976), where the transferred to the overlying and less gravi- youngest stellar population is also found" tationally bound material (Bruenn 1975) . Since Arnett, Buchler, and Livio are dis- Bruenn, Arnett, and Schramm (1977) have ana- lyzed the detailed calculations of Wilson (1974, 1976), Chechetkin et a1 . (1977), and This mass range would correspond to stars several others, to clarify the interplay that burn their carbon in non-degenerate between neutrino energy and momentum deposit conditions (Barkat, Reiss, and Rakavy 1974) tion and core bounce. but where carbon burning resultsin the for-, Continued improvements in the calculation of mation of an electron-degenerate 0-*-Mg neutrino opacities (Sato 1975, Nadyozhin core.The evolution of such a core, sur- 1977, Arnett 1977b) have led to the impor- rounded by a carbon burning shell, has been tant conclusion that neutrinos are trapped studied by Miyaji et a1 . (1979) . Electron during collapse for densities p > lo1 2g ~m-~.captures compete with explosive oxygen bur- Adiabatic hydrodynamics thus provides a good ning and lead to core collapse, with possi- approximation to the collapse of the inner ble ejection of the envelope due to explo- core. Van Riper (1978, 1979), and Van Riper sive carbon and helium burning.The discus- and Arnett (1978), find mass ejection by a sion of this mass range is closely related reflected shock, with the appropriate ener- to'that of the intermediate-mass stars.
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