Eur. Phys. J. C (2017) 77:596
DOI 10.1140/epjc/s10052-017-5149-2
Regular Article - Theoretical Physics
A comparative study on generalized model of anisotropic compact
star satisfying the Karmarkar condition
Piyali Bhar
1,a
, Ksh. Newton Singh
2,b
, Nayan Sarkar
3,c
, Farook Rahaman
3,d
1
Department of Mathematics, Government General Degree College, Singur, Hooghly, West Bengal 712409, India
2
Department of Physics, National Defence Academy, Khadakwasla, Pune 411023, India
3
Department of Mathematics, Jadavpur University, Kolkata 700032, India
Received: 20 June 2017 / Accepted: 21 August 2017 / Published online: 9 September 2017
© The Author(s) 2017. This article is an open access publication
Abstract A new solution satisfying the Karmarkar con-
dition is presented here. We were first to have discov-
ered a hypergeometric function metric potential represent-
ing embedding class I spacetime. This new solution yields
finite values of metric potentials, density, pressure, redshift,
etc. and hence a non-singular solution. The solution is well
behaved with respect to the parameter n = 12 to n = 24
corresponding to a stable configuration of mass 2.01M
and
radius 9.1 km. The internal properties of the solution are very
different for n = 12 to n = 24; however, the total mass and
radius is independent of the parameter n. The energy con-
ditions are also holds good by the solution which thus can
represent a physically viable matter distribution. The equi-
librium condition and stability are also discussed through
TOV-equation, cracking method and >4/3. The static
stability criterion is also well satisfied and the turning point
corresponds to 4.46M
for a radius of 9.1 km.
1 Introduction
The final states of collapsing stars remain an exciting research
area in theoretical astrophysics. Now a days it is a well-
established theory that the final state of a main-sequence star
of mass of more than 8M
is most likely to form a neu-
tron star after a type IIa supernova. However, it is important
to keep in mind that such an evolution in single star sys-
tem is completely different from that of a binary star system.
Also accretion onto a white dwarf leads to a type Ia super-
nova left behind a neutron star as well. Accretion onto a
neutron star (NS) can also initiate a collapse once it crossed
a
e-mail: piyalibhar90@gmail.com
b
e-mail: ntnphy@gmail.com
c
e-mail: nayan.mathju@gmail.com
d
e-mail: rahaman@associates.iucaa.in
the Chandrashekhar limit of NS leading to the formation of
more dense objects like quark star (QS) and black hole. Neu-
tron stars and quark stars are the most dense objects ever
existing in the universe that can be practically observed. Due
to their compact nature, many exotic phases are expected to
be present in the interior such as pion condensation, neutron
superfluid, superconducting protons, asymptotic free quarks,
quark gluon plasma etc. Therefore, these compact objects are
the only laboratories existing for testing quantum chromo-
dynamics.
New compact stars other than NS and QS such as strange
stars (SSs) and boson stars (BSs) have also been proposed by
Witten [1], Farhi and Jaffe [2], Kaup [3], Ruffini and Bonaz-
zola [4]andColpietal.[5]. The matter at the interior of these
compact stars are not necessarily ideal fluids (isotropic pres-
sure); however, assuming non-ideal (anisotropic pressure)
fluid would be of more general consideration. The existence
of an anisotropic pressure is also highly possible at a den-
sity ∼10
14
g/cm
3
due to relativistic nuclear interaction [6],
the presence of solid core or the presence of type 3A super-
fluid [7], phase transitions [8], meson condensation [9], slow
rotation [10], a mixture of two gases [11] or strong magnetic
fields [12], and the presence of some electric charge. It is well
known that the behavior of a collapsing star is strongly influ-
enced by its initial static configuration. The evolution of a
collapsing star can be strongly influenced by the presence of
pressure anisotropy, electric charge, EoS, shear, radiations,
magnetic field etc. The initial configurations with the same
masses and radii for pressure isotropy and anisotropy when
undergoing collapse lead to a completely different tempera-
ture evolution at their later stages [13]. Hence, to study the
complete picture of the initial static configuration it is nec-
essary to track the evolution when collapse happens.
Schwarzschild [14] has shown that an incompressible fluid
sphere satisfies the Buchdahl condition 2M/R ≤ 8/9, which
implies an upper bound on the redshift z
max
≤ 2. High red-
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