Magnetic Field Effects on the Thermonuclear Combustion Front of Chandrasekhar Mass White Dwarfs

Ghezzi, Cristian R.; Pino, E. M. de Gouveia Dal; Horvath, J. E.

doi:10.1086/319091

Cited by 14 publications

(21 citation statements)

References 36 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As in the case of chemical laboratory flames (Gostintsev, Istratov & Shulenin 1988), thermonuclear flames probably develop a self‐similar behaviour due to the action of the hydrodynamic instabilities. Under this hypothesis of a self‐similar deflagration regime, the effective flame speed is well described by a fractal scaling law, as previously proposed by several authors (Woosley 1990; Timmes & Woosley 1992; Niemeyer & Hillebrandt 1995; Niemeyer & Woosley 1997; see also Ghezzi et al 2001, hereafter Paper I), namely Here, v lam is the laminar velocity (as obtained, for example, in Timmes & Woosley 1992), L max and l min are the maximum and minimum R–T wavelength perturbations, respectively (see Chandrasekhar 1981) and d is the fractal dimension, which may assume a range of values, 2 ≤ d < 3 (Woosley 1990; see also Paper I).…”

Section: Introductionsupporting

confidence: 73%

Asymmetric explosions of thermonuclear supernovae

Ghezzi

Pino

Horvath

2004

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

A Type Ia supernova explosion starts in a white dwarf as a laminar deflagration at the centre of the star and soon several hydrodynamic instabilities -in particular, the Rayleigh-Taylor (R-T) instability -begin to act. In previous work, we addressed the propagation of an initially laminar thermonuclear flame in the presence of a magnetic field assumed to be dipolar. We were able to show that, within the framework of a fractal model for the flame velocity, the front is affected by the field through the quenching of the R-T instability growth in the direction perpendicular to the field lines. As a consequence, an asymmetry develops between the magnetic polar and the equatorial axis that gives a prolate shape to the burning front. We have here computed numerically the total integrated asymmetry as the flame front propagates outward through the expanding shells of decreasing density of the magnetized white dwarf progenitor, for several chemical compositions. We have found that a total asymmetry of about 50 per cent is produced between the polar and equatorial directions for progenitors with a surface magnetic field B ∼ 5 × 10 7 G, and a composition 12 C = 0.2 and 16 O = 0.8 (in this case, the R-T instability saturates at scales ∼20 times the width of the flame front). This asymmetry is in good agreement with the inferred asymmetries from spectropolarimetric observations of very young supernova remnants, which have recently revealed intrinsic linear polarization interpreted as evidence of an asymmetric explosion in several objects, such as SN1999by, SN1996X and SN1997dt. Larger magnetic field strengths will produce even larger asymmetries. We have also found that for lighter progenitors (i.e. progenitors with smaller concentrations of 16 O and larger concentrations of 12 C) the total asymmetry is larger.

show abstract

Section: Introductionsupporting

confidence: 73%

Asymmetric explosions of thermonuclear supernovae

Ghezzi

Pino

Horvath

2004

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

show abstract

“…In the absence of a B-field n RT = (1/2π) gk∆ρ/2ρ and so l = 4πρv 2 lam /g∆ρ. However, in the equatorial direction, the presence of B is essential in modifying the dispersion relation for the RT instability which reads n RT B = 1/2π gk(∆ρ/2ρ − kB 2 /4πgρ) where k = 2π/λ , λ is the wavelength of the perturbation, and ∆ρ = ρ u − ρ d is the density difference between the upstream and downstream parts of the flame front [47]. Taking into account the velocity of the flame, the minimum cut-off length is given by the condition l e n RT B (l e ) = v lam , from which we derive the minimum scale in the equatorial direction l e = 8π(B 2 /8π + ρv 2 lam /2)/g∆ρ.…”

Section: Flames Instabilities and Asymmetriesmentioning

confidence: 99%

“…Notice that although this is based solely on a linear analysis, 3D numerical simulations of the development of the magnetic RT instability [49] reinforce the results of asymmetry here reported and also reveals a tendency for its amplification in the non-linear regime. This has interesting effects for thermonuclear supernovae [47,48] and neutron stars [43,57].…”

Section: Flames Instabilities and Asymmetriesmentioning

confidence: 99%

Magnetic Fields in High-Density Stellar Matter

Lugones¹

2005

AIP Conference Proceedings

View full text Add to dashboard Cite

Abstract. I briefly review some aspects of the effect of magnetic fields in the high density regime relevant to neutron stars, focusing mainly on compact star structure and composition, superconductivity, combustion processes, and gamma ray bursts. THE "MAGNETIC FIELD" OF "NEUTRON STARS"A large body of evidence now identifies the presence of strong magnetic fields at (or very near) the surface of neutron stars. Except for a few cases, all the estimations of the magnetic fields of these objects come from the timing measurements of pulsar slowdown. The pulsar is usually modelled as a rapidly rotating neutron star with a dipolar magnetic field configuration in which the rotation axis is not aligned with the dipole axis. Since the period of the pulsed emission is associated with the rotation period P, accurate observations of P and its time derivativesṖ,P, and even the third derivative of P, have been used to shed light on pulsar dynamics. Within this framework the dynamic equation readsΩ = KΩ 3 , with K ≡ (R 6 B 2 p sin 2 α)/(6c 3 I), and Ω = 2π/P. Therefore, some properties of pulsars are plausible of interpretation in terms of timing data, e.g.:• the component of the B-field at the magnetic pole along the rotation axis(1)• the pulsar age t (or alternatively the rotational period at birth P i ),where τ ≡ −P/2Ṗ is the so called characteristic age, I is the moment of inertia of the neutron star, R its radius, and α is the angle between the rotation axis and the dipole axis. Note that, for determining B ⊥ the values of I and R must be assumed based mostly on theoretical arguments. A test of the reliability of these estimates, can be obtained from an independent determination of the age of the pulsar, which is possible for pulsars associated with supernova remnants (SNRs). Assuming that a given pulsar and a given SNR were born together, we can identify t SNR (the SNR age) with the pulsar age t in Eq. (2). Since within the dipole model τ is an upper limit for t, a comparison of t SNR with τ provides a relevant

show abstract

“…An important problem is to understand the role played by such an amplified magnetic field in the approach to and evolution after ignition of a type Ia supernova. For example, Ghezzi et al (2001), recently pointed out that a large‐scale magnetic field of 10 8 –10 9 G can generate asymmetries in the thermonuclear flame front that engulfs the white dwarf during the supernova. Our results show that the prior evolution of the field during accretion should be taken into account.…”

Section: Implications For Observed Systemsmentioning

confidence: 99%

Magnetic field evolution in accreting white dwarfs

Cumming

2002

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

We discuss the evolution of the magnetic field of an accreting white dwarf. We calculate the ohmic decay modes for accreting white dwarfs, the interiors of which are maintained in a liquid state by compressional heating. We show that the lowest‐order ohmic decay time is (8–12)×109 yr for a dipole field, and (4–6)×109 yr for a quadrupole field. We then compare the time‐scales for ohmic diffusion and accretion at different depths in the star, and for a simplified field structure and assuming spherical accretion, study the time‐dependent evolution of the global magnetic field at different accretion rates. We neglect mass loss by classical nova explosions and assume that the white dwarf mass increases with time. In this case, the field structure in the outer layers of the white dwarf is modified significantly for accretion rates above the critical rate M˙c≈(1–5)×10‐10 M⊙ yr‐1. We consider the implications of our results for observed systems. We propose that accretion‐induced magnetic field changes are the missing evolutionary link between AM Her systems and intermediate polars. The shorter ohmic decay time for accreting white dwarfs provides a partial explanation of the lack of accreting systems with ≈109 G fields. In rapidly accreting systems such as supersoft X‐ray sources, amplification of internal fields by compression may be important for type Ia supernova ignition and explosion. Finally, spreading matter in the polar cap may induce complexity in the surface magnetic field, and explain why the more strongly accreting pole in AM Her systems has a weaker field. We conclude with speculations concerning the field evolution when classical nova explosions cause the white dwarf mass to decrease with time.

show abstract

Magnetic Field Effects on the Thermonuclear Combustion Front of Chandrasekhar Mass White Dwarfs

Cited by 14 publications

References 36 publications

Asymmetric explosions of thermonuclear supernovae

Asymmetric explosions of thermonuclear supernovae

Magnetic Fields in High-Density Stellar Matter

Magnetic field evolution in accreting white dwarfs

Contact Info

Product

Resources

About