Research On The Structure And Property Of Massive Compact Stars

Recently,two massive neutron stars: PSR J1614+2230(with mass 1.97?0.04M?)and PSR J0348+0432(with mass 2.01?0.04M?)have been observed.In the framework of general relativity,by using the TOV equation,a soft equation of state(EOS)of dense matter cannot support a massive neutron star with mass up to 2.0 M?.However,the analysis of the laboratory data from the heavyion collisions and the correlated theoretical research prefer a soft EOS for the usymmetric dense matters;and the presence of hyperons at density exceeding 2~3 times of normal nuclear density0? also may soften the EOS of the dense matter.This situation promotes a challenge between the astro-observation and nuclear physics.In this work,we introduce an effective mechanism to answer this challenge,that is,if a neutron star is electrically charged,a soft EOS will be equivalently stiffened and thus can support a massive neutron star.By employing a representative soft EOS,it is found that in order to obtain an evident effect on the EOS and thus increasing the maximum stellar mass by the electrostatic field,the total net charge should be in an order of 1020 C.Moreover,by comparing the results of two kinds of charge distributions,it is found that even for different distribution,a similar total charge: ～ 2.3 × 1020 C is needed to support a ～ 2.0M⊙ neutron star.In this work,we also give a roughly discussion for the stability of the charged neutron star,and it is found that the charged neutron star is dynamical stable.Actually,there is a similar problem for another compact star,white dwarf.It is generally believed that when the mass of a white dwarf in the binary system approaches the Chandrasekhar mass limit 1.44⊙,type-Ia supernovae(SN Ia)will happen.Due to this unique feature,SN Ia can be regarded as standard candles for measuring far distances and thus in understanding the expansion history of the universe.However,some SN Ia dwarfs with exceptionally higher luminosity,such as SN 2003 fg,SN 2006 gz,SN 2007 if and SN 2009 dc have been observed.The luminosity of this group of SN Ia implies that their progenitors ought to be white dwarfs with super-Chandrasekhar masses lying in a range of 2.1–2.8⊙.Obviously,in the classical theoretical framework one cannot give a satisfactory explanation for the new observations as the EOS of free electron gas only can support a white dwarf with a maximum 1.44⊙ in Newtonian gravity.To solve this contradictory,we have introduced two mechanism:(1)Consider modified theories of gravity,Eddington-inspired Born-Infeld(EiBI)gravity,(2)Assume dark matter particles are distributed in white dwarf.Firstly,By employing the Eddington-inspired Born–Infeld(EiBI)gravity,we reinvestigate the structures and properties of white dwarfs,and find out that the EiBI gravity provides a new way to understand the observations.It is shown that by choosing an appropriate positive Eddington parameter ,a massive white dwarf with mass up to 2.8⊙ can be supported by the EOS free electron gas.On the other hand,if the gravity in the massive white dwarf really behaves as the EiBI gravity predicts,then one can obtain a constraint on the Eddington parameter in the Ei BI gravity.Moreover,we find out that the fast Keplarian frequency of the massive white dwarf raises a degeneration between the two kinds of compact stars,that is,one cannot distinguish whether the observed massive pulsar is a massive neutron star or a massive white dwarf only through the observed pulse frequency and mass.Secondly,Dark matter is believed to be a major component of our universe.So,we propose a new mechanism base on dark matter inspired super-Chandrasekhar mass white dwarf to explain the recent observation of super luminous type Ia supernovae explosions.Our calculation shows when a white dwarf accretes enough dark matter,due to the Pauli exclusive principle between fermionic darkmatter particles,the mass of corresponding dark white dwarf(which means the white dwarf mixed with dark matters)can significantly exceeds the Chandrasekhar limit.Moreover,we investigate some physical observable quantities,such as the redshift and moment of inertia of the dark white dwarf and found that these quantities are sensitive to the dark matter particle’s distribu-tions and thus can be potentially used to probe the relevant information of dark matter particles in the future.