Banibrata Mukhopadhyay

The Inter-University Centre for Astronomy and Astrophysics, Poona, Mahārāshtra, India

Are you Banibrata Mukhopadhyay?

Claim your profile

Publications (71)224.21 Total impact

  • Upasana Das, Banibrata Mukhopadhyay
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
  • Source
    Sujit Kumar Nath, Banibrata Mukhopadhyay
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate the evolution of hydromagnetic perturbations in a small section of accretion disks. It is known that molecular viscosity is negligible in accretion disks. Hence, it has been argued that a mechanism, known as Magnetorotational Instability (MRI), is responsible for transporting matter in the presence of weak magnetic field. However, there are some shortcomings, which question effectiveness of MRI. Now the question arises, whether other hydromagnetic effects, e.g. transient growth (TG), can play important role to bring nonlinearity in the system, even at weak magnetic fields. Otherwise, whether MRI or TG, which is primarily responsible to reveal nonlinearity to make the flow turbulent? Our results prove explicitly that the flows with high Reynolds number (Re), which is the case of realistic astrophysical accretion disks, exhibit nonlinearity by TG of perturbation modes faster than that by modes producing MRI. For a fixed wavevector, MRI dominates over transient effects, only at low Re, lower than its value expected to be in astrophysical accretion disks, and low magnetic fields. This seriously questions (overall) suasiveness of MRI in astrophysical accretion disks.
  • Upasana Das, Banibrata Mukhopadhyay
    Physical Review D 01/2015; 91(2). DOI:10.1103/PhysRevD.91.029905 · 4.86 Impact Factor
  • Upasana Das, Banibrata Mukhopadhyay
    [Show abstract] [Hide abstract]
    ABSTRACT: We show that the upper bound for the central magnetic field of a super-Chandrasekhar white dwarf calculated by Nityananda and Konar [Phys. Rev. D 89, 103017 (2014)] and in the concerned comment, by the same authors, against our work [U. Das and B. Mukhopadhyay, Phys. Rev. D 86, 042001 (2012)] is erroneous. This in turn strengthens the argument in favor of the stability of the recently proposed magnetized super-Chandrasekhar white dwarfs. We also point out several other numerical errors in their work. Overall we conclude that the arguments put forth by Nityananda and Konar are misleading.
    Physical Review D 01/2015; 91(2). DOI:10.1103/PhysRevD.91.028302 · 4.86 Impact Factor
  • Source
    Upasana Das, Banibrata Mukhopadhyay
    [Show abstract] [Hide abstract]
    ABSTRACT: The topic of magnetized super-Chandrasekhar white dwarfs is in the limelight, particularly in the last few years, since our proposal of their existence. By full-scale general relativistic magnetohydrodynamic (GRMHD) numerical analysis, we confirm in this work the existence of stable, highly magnetized, significantly super-Chandrasekhar white dwarfs with mass more than 3 solar mass. While a poloidal field geometry renders the white dwarfs oblate, a toroidal field makes them prolate retaining an overall quasi-spherical shape, as speculated in our earlier work. These white dwarfs are expected to serve as the progenitors of over-luminous type Ia supernovae.
    Journal of Cosmology and Astroparticle Physics 11/2014; 2015(05). DOI:10.1088/1475-7516/2015/05/016 · 5.88 Impact Factor
  • Source
    Upasana Das, Banibrata Mukhopadhyay
    [Show abstract] [Hide abstract]
    ABSTRACT: 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 show that modification of Einstein's gravity leads to significantly sub- and super-Chandrasekhar limiting masses, determined by a single model parameter. Explosions of these sub- and super-Chandrasekhar limiting mass white dwarfs explain under- and over-luminous SNeIa respectively, thus unifying these two apparently disjoint sub-classes. Our discovery raises two fundamental questions. Is the Chandrasekhar limit unique? Is Einstein's gravity the ultimate theory for understanding astronomical phenomena? Both answers appear to be no!
    Journal of Cosmology and Astroparticle Physics 11/2014; 2015(05). DOI:10.1088/1475-7516/2015/05/045 · 5.88 Impact Factor
  • Banibrata Mukhopadhyay
    [Show abstract] [Hide abstract]
    ABSTRACT: A Comment on the Letter by F. Iocco and M. Pato, Phys. Rev. Lett. 109, 021102 (2012). The authors of the Letter offer a Reply.
    Physical Review Letters 06/2014; 112(22):229001. DOI:10.1103/PhysRevLett.112.229001 · 7.73 Impact Factor
  • Source
    Upasana Das, Banibrata Mukhopadhyay
    [Show abstract] [Hide abstract]
    ABSTRACT: We show that the upper bound for the central magnetic field of a super-Chandrasekhar white dwarf calculated by Nityananda and Konar [Phys. Rev. D 89, 103017 (2014)] is completely erroneous. This in turn strengthens the argument in favor of the stability of the recently proposed magnetized super-Chandrasekhar white dwarfs. We also point out several other numerical errors in their work. Overall we conclude, based on our calculations, that the arguments put forth by Nityananda and Konar are fallacious and misleading.
  • Source
    Upasana Das, Banibrata Mukhopadhyay
    [Show abstract] [Hide abstract]
    ABSTRACT: We address the issue of stability of recently proposed significantly super-Chandrasekhar white dwarfs. We present stable solutions of magnetostatic equilibrium models for super-Chandrasekhar white dwarfs pertaining to various magnetic field profiles. This has been obtained by self-consistently including the effects of the magnetic pressure gradient and total magnetic density in a general relativistic framework. We estimate that the maximum stable mass of magnetized white dwarfs could be more than 3 solar mass. This is very useful to explain peculiar, overluminous type Ia supernovae which do not conform to the traditional Chandrasekhar mass-limit.
    Journal of Cosmology and Astroparticle Physics 04/2014; 2014(06). DOI:10.1088/1475-7516/2014/06/050 · 5.88 Impact Factor
  • Source
    Indrani Banerjee, Banibrata Mukhopadhyay
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate nucleosynthesis inside the outflows from gamma-ray burst (GRB) accretion disks formed by the Type II collapsars. In these collapsars, massive stars undergo core collapse to form a proto-neutron star initially and a mild supernova explosion is driven. The supernova ejecta lack momentum and subsequently this newly formed neutron star gets transformed to a stellar mass black hole via massive fallback. The hydrodynamics and the nucleosynthesis in these accretion disks has been studied extensively in the past. Several heavy elements are synthesized in the disk and much of these heavy elements are ejected from the disk via winds and outflows. We study nucleosynthesis in the outflows launched from these disks by using an adiabatic, spherically expanding outflow model, to understand which of these elements thus synthesized in the disk survive in the outflow. While studying this we find that many new elements like isotopes of titanium, copper, zinc etc. are present in the outflows. 56Ni is abundantly synthesized in most of the cases in the outflow which implies that the outflows from these disks in a majority of cases will lead to an observable supernova explosion. It is mainly present when outflow is considered from the He-rich, 56Ni/54Fe rich zones of the disks. However, outflow from the Si-rich zone of the disk remains rich in silicon. Although, emission lines of many of these heavy elements have been observed in the X-ray afterglows of several GRBs by Chandra, BeppoSAX, XMM-Newton etc., Swift seems to have not detected these lines yet.
    The Astrophysical Journal 09/2013; 778(1). DOI:10.1088/0004-637X/778/1/8 · 6.28 Impact Factor
  • Source
    Indrani Banerjee, Banibrata Mukhopadhyay
    [Show abstract] [Hide abstract]
    ABSTRACT: Stellar mass black holes (SMBHs), forming by the core collapse of very massive, rapidly rotating stars, are expected to exhibit a high density accretion disk around them developed from the spinning mantle of the collapsing star. A wide class of such disks, due to their high density and temperature, are effective emitters of neutrinos and hence called neutrino cooled disks. Tracking the physics relating the observed (neutrino) luminosity to the mass, spin of black holes (BHs) and the accretion rate (M[over ˙]) of such disks, here we establish a correlation between the spin and mass of SMBHs at their formation stage. Our work shows that spinning BHs are more massive than nonspinning BHs for a given M[over ˙]. However, slowly spinning BHs can turn out to be more massive than spinning BHs if M[over ˙] at their formation stage was higher compared to faster spinning BHs.
    Physical Review Letters 08/2013; 111(6):061101. DOI:10.1103/PhysRevLett.111.061101 · 7.73 Impact Factor
  • Source
    Sujit Kumar Nath, Banibrata Mukhopadhyay, Amit K Chattopadhyay
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate the evolution of magnetohydrodynamic (or hydromagnetic as coined by Chandrasekhar) perturbations in the presence of stochastic noise in rotating shear flows. The particular emphasis is the flows whose angular velocity decreases but specific angular momentum increases with increasing radial coordinate. Such flows, however, are Rayleigh stable but must be turbulent in order to explain astrophysical observed data and, hence, reveal a mismatch between the linear theory and observations and experiments. The mismatch seems to have been resolved, at least in certain regimes, in the presence of a weak magnetic field, revealing magnetorotational instability. The present work explores the effects of stochastic noise on such magnetohydrodynamic flows, in order to resolve the above mismatch generically for the hot flows. We essentially concentrate on a small section of such a flow which is nothing but a plane shear flow supplemented by the Coriolis effect, mimicking a small section of an astrophysical accretion disk around a compact object. It is found that such stochastically driven flows exhibit large temporal and spatial autocorrelations and cross-correlations of perturbation and, hence, large energy dissipations of perturbation, which generate instability. Interestingly, autocorrelations and cross-correlations appear independent of background angular velocity profiles, which are Rayleigh stable, indicating their universality. This work initiates our attempt to understand the evolution of three-dimensional hydromagnetic perturbations in rotating shear flows in the presence of stochastic noise.
    Physical Review E 07/2013; 88(1-1):013010. DOI:10.1103/PhysRevE.88.013010 · 2.33 Impact Factor
  • Source
    Upasana Das, Banibrata Mukhopadhyay
    [Show abstract] [Hide abstract]
    ABSTRACT: Is the Chandrasekhar mass limit for white dwarfs (WDs) set in stone? Not anymore -- recent observations of over-luminous, peculiar type Ia supernovae can be explained if significantly super-Chandrasekhar WDs exist as their progenitors, thus barring them to be used as cosmic distance indicators. However, there is no estimate of a mass limit for these super-Chandrasekhar WD candidates yet. Can they be arbitrarily large? In fact, the answer is no! We arrive at this revelation by exploiting the flux freezing theorem in observed, accreting, magnetized WDs, which brings in Landau quantization of the underlying electron degenerate gas. This essay presents the calculations which pave the way for the ultimate (significantly super-Chandrasekhar) mass limit of WDs, heralding a paradigm shift 80 years after Chandrasekhar's discovery.
    International Journal of Modern Physics D 05/2013; 22(12). DOI:10.1142/S0218271813420042 · 1.42 Impact Factor
  • Source
    Indrani Banerjee, Banibrata Mukhopadhyay
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate nucleosynthesis inside the gamma-ray burst (GRB) accretion disks formed by the Type II collapsars. In these collapsars, the core collapse of massive stars first leads to the formation of a proto-neutron star and a mild supernova explosion is driven. However, this supernova ejecta lack momentum and falls back onto the neutron star which gets transformed to a stellar mass black hole. In order to study the hydrodynamics and nucleosynthesis of such an accretion disk formed from the fallback material of the supernova ejecta, we use the well established hydrodynamic models. In such a disk neutrino cooling becomes important in the inner disk where the temperature and density are higher. Higher the accretion rate (dot{M}), higher is the density and temperature in the disks. In this work we deal with accretion disks with relatively low accretion rates: 0.001 M_sun s^{-1} \lesssim dot{M} \lesssim 0.01 M_sun s^{-1} and hence these disks are predominantly advection dominated. We use He-rich and Si-rich abundances as the initial condition of nucleosynthesis at the outer disk, and being equipped with the disk hydrodynamics and the nuclear network code, we study the abundance evolution as matter inflows and falls into the central object. We investigate the variation in the nucleosynthesis products in the disk with the change in the initial abundance at the outer disk and also with the change in the mass accretion rate. We report the synthesis of several unusual nuclei like {31}P, {39}K, {43}Sc, {35}Cl, and various isotopes of titanium, vanadium, chromium, manganese and copper. We also confirm that isotopes of iron, cobalt, nickel, argon, calcium, sulphur and silicon get synthesized in the disk, as shown by previous authors. Much of these heavy elements thus synthesized are ejected from the disk via outflows and hence they should leave their signature in observed data.
    Research in Astronomy and Astrophysics 05/2013; 13(9). DOI:10.1088/1674-4527/13/9/005 · 1.52 Impact Factor
  • Source
    Upasana Das, Banibrata Mukhopadhyay
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Modern Physics Letters A 04/2013; 29(07). DOI:10.1142/S0217732314500357 · 1.34 Impact Factor
  • Upasana Das, Banibrata Mukhopadhyay, A. R. Rao
    [Show abstract] [Hide abstract]
    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.
    The Astrophysical Journal Letters 03/2013; 767(1):L14. DOI:10.1088/2041-8205/767/1/L14 · 5.60 Impact Factor
  • Source
    Dataset: NUPHA19373
    Monika Sinha, Banibrata Mukhopadhyay, Armen Sedrakian
  • Source
    Upasana Das, Banibrata Mukhopadhyay
    [Show abstract] [Hide abstract]
    ABSTRACT: 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. We obtain the mass-radius relations for such white dwarfs and show that it is possible to have magnetized white dwarfs with a mass significantly greater than the Chandrasekhar limit in the range 2.3 - 2.6 M_sun. Recent observations of peculiar type Ia supernovae - SN 2006gz, SN 2007if, SN 2009dc, SN 2003fg - seem to suggest super-Chandrasekhar-mass white dwarfs with masses up to 2.4 - 2.8 M_sun, as their most likely progenitors and interestingly our results lie within the observational limits.
  • Source
    Indrani Banerjee, Banibrata Mukhopadhyay
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate nucleosynthesis inside the gamma-ray burst (GRB) accretion disks formed by the Type II collapsars and outflows launched from these disks. We deal with accretion disks having relatively low accretion rates: 0.001 M_sun s^{-1} <~ Mdot <~ 0.01 M_sun s^{-1} and hence they are predominantly advection dominated. We report the synthesis of several unusual nuclei like 31P, 39K, 43Sc, 35Cl and various isotopes of titanium, vanadium, chromium, manganese and copper in the disk. We also confirm that isotopes of iron, cobalt, nickel, argon, calcium, sulphur and silicon get synthesized in the disk, as shown by previous authors. Much of these heavy elements thus synthesized are ejected from the disk and survive in the outflows. Indeed, emission lines of many of these heavy elements have been observed in the X-ray afterglows of several GRBs.
  • Source
    Banibrata Mukhopadhyay, Monika Sinha
    [Show abstract] [Hide abstract]
    ABSTRACT: The magnetars are believed to be highly magnetized neutron stars having surface magnetic field 10^{14} - 10^{15} G. It is believed that at the center, the magnetic field may be higher than that at the surface. We study the effect of the magnetic field on the neutron star matter. We model the nuclear matter with the relativistic mean field approach considering the possibility of appearance of hyperons at higher density. We find that the effect of magnetic field on the matter of neutron stars and hence on the mass-radius relation is important, when the central magnetic field is atleast of the order of 10^{17} G. Very importantly, the effect of strong magnetic field reveals anisotropy to the system. Moreover, if the central field approaches 10^{19} G, then the matter becomes unstable which limits the maximum magnetic field at the center of magnetars.

Publication Stats

502 Citations
224.21 Total Impact Points

Institutions

  • 2002–2008
    • The Inter-University Centre for Astronomy and Astrophysics
      Poona, Mahārāshtra, India
    • Physical Research Laboratory
      Amadavad, Gujarat, India
  • 2003–2007
    • Harvard-Smithsonian Center for Astrophysics
      • Institute for Theory and Computation
      Cambridge, Massachusetts, United States
  • 2004
    • University of Oulu
      • Astronomy
      Uleoborg, Oulu, Finland