A POSSIBLE EVOLUTIONARY SCENARIO OF HIGHLY MAGNETIZED SUPER-CHANDRASEKHAR WHITE DWARFS: PROGENITORS OF PECULIAR TYPE Ia SUPERNOVAE

Abstract

Several recently discovered peculiar Type Ia supernovae seem to demand an altogether new formation theory that might help explain the puzzling dissimilarities between them and the standard Type Ia supernovae. The most striking aspect of the observational analysis is the necessity of invoking super-Chandrasekhar white dwarfs having masses ∼2.1-2.8 M , M being the mass of Sun, as their most probable progenitors. Strongly magnetized white dwarfs having super-Chandrasekhar masses have already been established as potential candidates for the progenitors of peculiar Type Ia supernovae. Owing to the Landau quantization of the underlying electron degenerate gas, theoretical results yielded the observationally inferred mass range. Here, we sketch a possible evolutionary scenario by which super-Chandrasekhar white dwarfs could be formed by accretion on to a commonly observed magnetized white dwarf, invoking the phenomenon of flux freezing. This opens multiple possible evolution scenarios ending in supernova explosions of super-Chandrasekhar white dwarfs having masses within the range stated above. We point out that our proposal has observational support, such as the recent discovery of a large number of magnetized white dwarfs by the Sloan Digital Sky Survey.

Revisiting some physics issues related to the new mass limit for magnetized white dwarfs

“…This is maintained as long as B surf is several orders of magnitude lower than B cent , such that the surface magnetic pressure is much less compared to the central magnetic pressure. If this is true, which indeed we have always argued for in our works [1,2,3,4,5,6], then one can easily see that B avg ≈ B cent /2. Thus, for the super-Chandrasekhar white dwarf having mass 2.58M ⊙ and B cent = 8.8 × 10…”

“…17 G, we obtain B avg = 4.4 × 10 17 G. Note that, although a large B brings in anisotropy in the system, which may lead the star to become a spheroid, making a general relativistic treatment indispensable, in our works [1,2,3,4,5,6] we stuck to the Newtonian framework assuming the star to be spherical. Therefore, in that case, the overall isotropic magnetic pressure would be P B = B 2 /24π.…”

“…Models have also been proposed which invoke the merger of two white dwarfs, known as the double degenerate scenario [20]. On a fundamentally different ground, the strongly magnetized super-Chandrasekhar white dwarfs proposed by Das & Mukhopadhyay [2,4] and Das, Mukhopadhyay & Rao [5] can explain these supernova explosions, which is the indirect evidence for the existence of super-Chandrasekhar white dwarfs. However, there has been no direct detection of such white dwarfs so far.…”

“…G (see, e.g., Figure 1 of [5]), B equi = 5.77 × 10 16 G ≫ 10 12 G. Now this B equi has to be compared with the average field (B avg ), as obtained by us, for the white dwarf under consideration. In order to estimate B avg , we define B avg ≈ (B cent + B surf )/2, where B surf denotes the surface magnetic field.…”

Revised density of magnetized nuclear matter at the neutron drip line

“…The significant change in the drip density arises only in the linear regime. For instance, the drip density for the ionic system increases by an order, compared to that of the nonmagnetic gas, for a field ∼ 6.4 × 10 17 G. Apart from the various applications to neutron stars, the present findings may have interesting consequences to the recently proposed high density ( 10 11 gm/cc), high magnetic field ( 10 15 G) white dwarfs [4,12,13,15,16]. The inner region of white dwarfs, in particular for B int 10 17 G, would have been neutronized if the drip density had not been changed with the field.…”