Significantly super-Chandrasekhar limiting mass white dwarfs and their consequences (original) (raw)
Related papers
New Mass Limit for White Dwarfs: Super-Chandrasekhar Type Ia Supernova as a New Standard Candle
Physical Review Letters, 2013
Type Ia supernovae, sparked off by exploding white dwarfs of mass close to Chandrasekhar limit, play the key role to understand the expansion rate of universe. However, recent observations of several peculiar type Ia supernovae argue for its progenitor mass to be significantly super-Chandrasekhar. We show that strongly magnetized white dwarfs not only can violate the Chandrasekhar mass limit significantly, but exhibit a different mass limit. We establish from foundational level that the generic mass limit of white dwarfs is 2.58 solar mass. This explains the origin of over-luminous peculiar type Ia supernovae. Our finding further argues for a possible second standard candle, which has many far reaching implications, including a possible reconsideration of the expansion history of the universe.
2015
Since 2012, we have initiated developing systematically the simplistic to rigorous models to prove that highly super-Chandrasekhar, as well as highly sub-Chandrasekhar, limiting mass white dwarfs are possible to exist. We show that the mass of highly magnetized or modified Einstein's gravity induced white dwarfs could be significantly super-Chandrasekhar and such white dwarfs could altogether have a different mass-limit. On the other hand, type Ia supernovae (SNeIa), a key to unravel the evolutionary history of the universe, are believed to be triggered in white dwarfs having mass close to the Chandrasekhar-limit. However, observations of several peculiar, over-and under-luminous SNeIa argue for exploding masses widely different from this limit. We argue that explosions of super-Chandrasekhar limiting mass white dwarfs result in over-luminous SNeIa. We arrive at this revelation, first by considering simplistic, spherical, Newtonian white dwarfs with constant magnetic fields. Then we relax the Newtonian assumption and consider the varying fields, however obtain similar results. Finally, we consider a full scale general relativistic magnetohydrodynamic description of white dwarfs allowing their self-consistent departure from a sphere to ellipsoid. Subsequently, we also explore the effects of modified Einstein's gravity. Our finding questions the uniqueness of the Chandrasekhar-limit. It further argues for a possible second standard candle, which has many far reaching implications.
Violation of Chandrasekhar Mass Limit: The Exciting Potential of Strongly Magnetized White Dwarfs
International Journal of Modern Physics D, 2012
We consider a relativistic, degenerate, electron gas under the influence of a strong magnetic field, which describes magnetized white dwarfs. Landau quantization changes the density of states available to the electrons, thus modifying the underlying equation of state. In the presence of very strong magnetic fields a maximum of either one, two or three Landau level(s) is/are occupied. We obtain the mass–radius relations for such white dwarfs and their detailed investigation leads us to propose the existence of white dwarfs having a mass ~2.3M⊙, which overwhelmingly exceeds the Chandrasekhar mass limit.
Strong constraints on magnetized white dwarfs surpassing the Chandrasekhar mass limit
Physical Review D, 2014
We show that recently proposed white dwarf models with masses well in excess of the Chandrasekhar limit, based on modifying the equation of state by a super-strong magnetic field in the centre, are very far from equilibrium because of the neglect of Lorentz forces. An upper bound on the central magnetic fields, from a spherically averaged hydrostatic equation, is much smaller than the values assumed. Robust estimates of the Lorentz forces are also made without assuming spherical averaging. These again bear out the results obtained from a spherically averaged model. In our assessment, these estimates rule out the possibility that magnetic tension could change the situation in favor of larger magnetic fields. We conclude that such super-Chandrasekhar models are unphysical and exploration of their astrophysical consequences is premature.
Revisiting some physics issues related to the new mass limit for magnetized white dwarfs
Modern Physics Letters A, 2014
We clarify important physics issues related to the recently established new mass limit for magnetized white dwarfs which is significantly super-Chandrasekhar. The issues include, justification of high magnetic field and the corresponding formation of stable white dwarfs, contribution of the magnetic field to the total density and pressure, flux freezing, variation of magnetic field and related currents therein. We also attempt to address the observational connection of such highly magnetized white dwarfs.
Mass of highly magnetized white dwarfs exceeding the Chandrasekhar limit: An analytical view
In recent years a number of white dwarfs has been observed with very high surface magnetic fields. We can expect that the magnetic field in the core of these stars would be much higher (~ 10^{14} G). In this paper, we analytically study the effect of high magnetic field on relativistic cold electron, and hence its effect on the stability and the mass-radius relation of a magnetic white dwarf. In strong magnetic fields, the equation of state of the Fermi gas is modified and Landau quantization comes into play. For relatively very high magnetic fields (with respect to the energy density of matter) the number of Landau levels is restricted to one or two. We analyse the equation of states for magnetized electron degenerate gas analytically and attempt to understand the conditions in which transitions from the zero-th Landau level to first Landau level occur. We also find the effect of the strong magnetic field on the star collapsing to a white dwarf, and the mass-radius relation of the resulting star. We obtain an interesting theoretical result that it is possible to have white dwarfs with mass more than the mass set by Chandrasekhar limit.
Stability of super-Chandrasekhar magnetic white dwarfs
Physical Review D, 2013
It has been recently proposed that very massive white dwarfs endowed with strongly quantizing magnetic fields might be the progenitors of overluminous type Ia supernovae like SN 2006gz and SN 2009dc. In this work, we show that the onset of electron captures and pycnonuclear reactions in these putative super-Chandrasekhar white dwarfs may severely limit their stability. On the other hand, we find that general relativity does not lead to global instabilities.
Journal of Cosmology and Astroparticle Physics, 2015
We explore the effect of modification to Einstein's gravity in white dwarfs for the first time in the literature, to the best of our knowledge. This leads to significantly suband super-Chandrasekhar limiting masses of white dwarfs, determined by a single model parameter. On the other hand, type Ia supernovae (SNeIa), a key to unravel the evolutionary history of the universe, are believed to be triggered in white dwarfs having mass close to the Chandrasekhar limit. However, observations of several peculiar, under-and over-luminous SNeIa argue for exploding masses widely different from this limit. We argue that explosions of the modified gravity induced sub-and super-Chandrasekhar limiting mass white dwarfs result in under-and over-luminous SNeIa respectively, thus unifying these two apparently disjoint sub-classes and, hence, serving as a missing link. Our discovery raises two fundamental questions. Is the Chandrasekhar limit unique? Is Einstein's gravity the ultimate theory for understanding astronomical phenomena? Both the answers appear to be no!
Imprint of modified Einstein’s gravity on white dwarfs: Unifying Type Ia supernovae
International Journal of Modern Physics D, 2015
We establish the importance of modified Einstein’s gravity (MG) in white dwarfs (WDs) for the first time in the literature. We show that MG leads to significantly sub- and super-Chandrasekhar limiting mass WDs, depending on a single model parameter. However, conventional WDs on approaching Chandrasekhar’s limit are expected to trigger Type Ia supernovae (SNeIa), a key to unravel the evolutionary history of the universe. Nevertheless, observations of several peculiar, under- and over-luminous SNeIa argue for the limiting mass widely different from Chandrasekhar’s limit. Explosions of MG induced sub- and super-Chandrasekhar limiting mass WDs explain under- and over-luminous SNeIa respectively, thus unifying these two apparently disjoint sub-classes. Our discovery questions both the global validity of Einstein’s gravity and the uniqueness of Chandrasekhar’s limit.
Highly magnetized white dwarfs: implications and current status
arXiv: High Energy Astrophysical Phenomena, 2021
Over the last decade or so, we have been developing the possible existence of highly magnetized white dwarfs with analytical stellar structure models. While the primary aim was to explain the nature of the peculiar overluminous type Ia supernovae, later on, these magnetized stars were found to have even wider ranging implications including those for white dwarf pulsars, soft gamma-ray repeaters and anomalous X-ray pulsars, as well as gravitational radiation. In particular, we have explored in detail the massradius relations for these magnetized stars and showed that they can be significantly different from the Chandrasekhar predictions which essentially leads to a new super-Chandrasekhar mass-limit. Recently, using the stellar evolution code STARS, we have successfully modelled their formation and cooling evolution directly from the magnetized main sequence progenitor stars. Here we briefly discuss all these findings and conclude with their current status in the scientific community.