Showing papers by "Jeremiah P. Ostriker published in 1971"

Do Pulsars Make Supernovae

Abstract: The hypothesis, that pulsars can produce supernova explosions of type II, is explored with the aid of detailed hydrodynamical calculations. Preliminary calculations performed with Gunn (1971) indicated that the electromagnetic energy radiated by a newly formed rotating, magnetic, neutron star could drive off the remaining envelope of a red giant star for stars having initial masses in the range 3–8 M ⊙. Here we present theoretical light curves obtained from hydrodynamic calculations with radiative diffusion and compare them with observations of supernovae. For the case of a star of original mass 4.5 M ⊙,light maximum is calculated to occur when the envelope, now in the form of a thin shell, has reached a radius of 9 × 1015 cm, a velocity of 7650 km s−1 and an effective temperature of 8000 K, at which point its optical thickness approaches unity. The early part of the light curve can be strongly affected by the presence or absence of a dust-laden circumstellar envelope. The temperature, luminosity, decay rate, and envelope velocity observed in the latter phases of type II supernovae are simulated with fair accuracy by the present model.

On the motion and radiation of charged particles in strong electromagnetic waves. I - Motion in plane and spherical waves

Abstract: Charge particle motion and radiation in strong plane and spherical electromagnetic waves with nonthermal astrophysical applications

Recent Developments in the Theory of Degenerate Dwarfs

Abstract: Stars exist by virtue of a stable balance between the forces of gravity and pressure. Of all the conceivable stars which might be represented by points on the mass-radius plane, only those occurring in four relatively small islands of stability arc known (or thought) to exist. The corresponding objects are supported by the pressure provided by the motions of four kinds of particles. Cold nucleon pressure allows neutron stars (d Wheeler 1966), cold electron pressure allows degenerate dwarfs, the subject of the present re­ view, thermal ion and electron pressure supports the ordinary stars, and photon radiation pressure the supermassive stars (d Wagoner 1969). While the radius increases by ",102 from class to class, the typical mass in each is­ land (excepting supermassive star.s which may not exist) is near one solar mass. Thus ordinary (",1 M0) stars can pass to either of the two condensed states without losing their identity, and their real (vs possible) existence might have been anticipated. Neutron stars were predicted in just this way, but degenerate dwarfs were discovered before our knowledge of physics was advanced enough to understand them. The original explanation (Chandrasekhar 1931a, b, 1935) of these very common stars has withstood the test of time. From the observed radii (",1O-2R0) and masses (�1M0)' the internal pressure ("",CM2/R4) greatly exceeds that available from thermal motions (for Tint.rior < 10s.o0K). How­ ever, the number density of electrons no is so high that the zero-point momen­ tum (P. "'" tm.l/3) provides enough pressure to support the stars at radii in the observed range. So long as the electron velocities are nonrelativistic, the degenerate pressure Pe ""Pe2neme-l depends on the density to the (5/3) power or on Mo/3R-5. Comparing this with the pressure required to support the star against self-gravitation ( oc M2R-4) we see that degenerate dwarfs supported by nonrelativistic electron motions have a mass-radius relation of the form Roc M-l/3. For sufficiently high mass, the electrons become relativistic, and the electron pressure Pe "" p.em. depends on the density to the (4/3) power or on M4/3R-4; it is no longer certain that a small enough radius can be found to bring the pressure and gravitational forces in balance. The maximum mass allowed for a spherical star-the Chandrasekhar mass limit-can b( seen

Runaway stars in the Gum Nebula

Abstract: It is proposed that the two pulsars PSR 0833-45 (the Vela pulsar) and MP 0835 are runaways from a common binary system originally located in the B association around gamma Velorum. Arguments are presented for a simple model of the Gum nebula in which two distinct ionized regions are present. The first consists of the Stromgren spheres of gamma Velorum and zeta Puppis, while the second is a larger, more filamentary region ionized by the supernova explosion associated with PSR 0833-45. Using this model and the available dispersion measures, the distances to the two pulsars were estimated and found to be compatible with a runaway origin. The position angle of the rotation axis of PSR 0833-45 is also compatible with this origin. The masses of the parent stars of the two pulsars can be deduced from the runaway star dynamics and an assumed age for MP 0835. It is concluded that the masses were in excess of 10 solar masses. The dynamically-determined parent star masses are in agreement with the values expected for evolved members of the B association around gamma Velorum.