在椭圆轨道的致密双星模型作为周期性重复快速射电暴(Fast Radio Bursts,FRBs)起源的基础上,考虑引力辐射对快速射电暴周期性行为的影响。这个双星系统包含一个具有强偶极磁场的中子星和一个磁化的白矮星。当白矮星充满它的洛希瓣时,物...在椭圆轨道的致密双星模型作为周期性重复快速射电暴(Fast Radio Bursts,FRBs)起源的基础上,考虑引力辐射对快速射电暴周期性行为的影响。这个双星系统包含一个具有强偶极磁场的中子星和一个磁化的白矮星。当白矮星充满它的洛希瓣时,物质将通过内拉格朗日点转移到中子星表面。由于角动量守恒,白矮星可能在一次爆发之后被踢开,接着在演化过程中由于引力辐射再次充满洛希瓣,实现再次爆发。这种情况下,快速射电暴的周期对应于双星轨道周期P_(orb),而它与两次质量转移时间间隔Δt之间的关系是能否显现周期性行为的关键因素。很明显,Δt≈P_(orb)或者Δt<P_(orb)是周期性行为显现的必要条件。反之,如果Δt>>P_(orb),周期性将很难观测到。结果表明,只有相对较长周期的快速射电暴才能显示周期性行为,这表明目前仅有的两个周期性快速射电暴都对应于较长的周期是合理的。展开更多
ASTEROSEISMOLOGY of pulsating white dwarfs is an effective tool for us to infer their internal structures and the activities of stars on the final stages of stellar evolution. DA-type pulsating white dwarfs, with hydr...ASTEROSEISMOLOGY of pulsating white dwarfs is an effective tool for us to infer their internal structures and the activities of stars on the final stages of stellar evolution. DA-type pulsating white dwarfs, with hydrogen-rich shells and low temperatures, constitute an instability strip in the H-R diagram, which have only 24 members. In order to push forward the research work in this field, many astronomers have devoted themselves to the search of new possible members for a long time. During two nights on February of 1996, the authors observed five candidates selected from the Kiso survey (Noguchi et al., 1980; Kondo et al., 1984), with the 1.93-m telescope at Observatoire de Haute-Provence, France. In the present note, we report the discovery of two new variables from this observation run: KUV 08368+4026 and KUV 11370+4222.展开更多
Using the linearized relativistic Vlasov-Maxwell equations,a generalized expression for the plasma conductivity tensor is derived.The dispersion relation for the O-mode in a relativistic degenerate electron plasma is ...Using the linearized relativistic Vlasov-Maxwell equations,a generalized expression for the plasma conductivity tensor is derived.The dispersion relation for the O-mode in a relativistic degenerate electron plasma is investigated by employing the Fermi-Dirac distribution function.The propagation characteristics of the O-mode（cut offs,resonances,propagation regimes,harmonic structure） are examined by using specific values of the density and the magnetic field that correspond to different relativistic dense environments.Further,it is observed that due to the relativistic effects the cut off and the resonance points are shifted to low frequency values,as a result the propagation regime is reduced.The dispersion relations for the non-relativistic and the ultra-relativistic limits are also presented.展开更多
Recently, U. Das and B. Mukhopadhyay proposed that the Chandrasekhar limit of a white dwarf could reach a new high level （2.58M） if a superstrong magnetic field were considered （Das U and Mukhopadhyay B 2013 Phys. ...Recently, U. Das and B. Mukhopadhyay proposed that the Chandrasekhar limit of a white dwarf could reach a new high level （2.58M） if a superstrong magnetic field were considered （Das U and Mukhopadhyay B 2013 Phys. Rev. Lett. 110 071102）, where the structure of the strongly magnetized white dwarf （SMWD） is calculated in the framework of Newtonian theory （NT）. As the SMWD has a far smaller size, in contrast with the usual expectation, we found that there is an obvious general relativistic effect （GRE） in the SMWD. For example, for the SMWD with a one Landau level system, the super-Chandrasekhar mass limit in general relativity （GR） is approximately 16.5% lower than that in NT. More interestingly, the maximal mass of the white dwarf will be first increased when the magnetic field strength keeps on increasing and reaches the maximal value M = 2.48MQ with BD = 391.5. Then if we further increase the magnetic fields, surprisingly, the maximal mass of the white dwarf will decrease when one takes the GRE into account.展开更多
Using a program written in Excel, it was found that a supernova remnant, with a mass between 1.44 and 2 solar masses, contracts down to a neutron star. During the collapse, the decreasing gravitational potential slows...Using a program written in Excel, it was found that a supernova remnant, with a mass between 1.44 and 2 solar masses, contracts down to a neutron star. During the collapse, the decreasing gravitational potential slows time. Here, the pressure becomes high enough to stop the contraction. At greater than 2.2 solar masses, while the remnant is still contracting, the gravitational potential causes time to relatively freeze at the center, and stop the contraction before the pressure gets high enough to stop it, as it did in a neutron star. This also freezes the flow of information concerning the decrease in gravitational potential, thus, the frozen portions remain frozen and do not contract down any further and become imaginary. On top of this frozen center, additional matter physically and relatively contracts and the radius of the freeze point moves out. If the freeze made its way to the surface, it would meet the condition of a black hole, having a Schwarzschild radius;but it does not quite get there. The surface is not quite frozen. Even though these “almost black holes” do not have an event horizon, they are almost as small as that described by the Schwarzschild radius and due to the gravitational red shift, are very hard to see. A black star has been created. A contracting white dwarf at the Chandrasekhar limit (1.44 solar masses) has a density of about 1 × 109 kg/m3. After it cools and then collapses into a neutron star, it will have a minimum density of 3.5 × 1015 kg/m3 near the surface. This article explains how these two densities relate to why there are no supernova created stellar black stars above 15 solar masses and why super massive black stars start at 50,000 solar masses? Extracting limits like these cannot be accomplished using the standard black hole model, but this black star model has revealed these size limits and a lot more.展开更多
Fast radio bursts (FRBs) at cosmological distances still hold concealed physical origins. Previously Liu (2018) proposes a scenario that the collision between a neutron star (NS) and a white dwarf (WD) can be one of t...Fast radio bursts (FRBs) at cosmological distances still hold concealed physical origins. Previously Liu (2018) proposes a scenario that the collision between a neutron star (NS) and a white dwarf (WD) can be one of the progenitors of non-repeating FRBs and notices that the repeating FRBs can also be explained if a magnetar formed after such NS-WD merger. In this paper, we investigate this channel of magnetar formation in more detail. We propose that the NS-WD post-merger, after cooling and angular momentum redistribution, may collapse to either a black hole or a new NS or even remains as a hybrid WDNS, depending on the total mass of the NS and WD. In particular, the newly formed NS can be a magnetar if the core of the WD collapsed into the NS while large quantities of degenerate electrons of the WD compressed to the outer layers of the new NS. A strong magnetic field can be formed by the electrons and positive charges with different angular velocities induced by the differential rotation of the newborn magnetar. Such a magnetar can power the repeating FRBs by the magnetic reconnections due to the crustal movements or starquakes.展开更多
快速射电暴(Fast Radio Bursts,FRBs)是来自河外的短暂而明亮的射电能量脉冲,有重复快速射电暴和非重复快速射电暴两种类型。重复快速射电暴的重复爆发行为可能源于一个具有强偶极磁场的中子星和磁化的白矮星组成的致密双星系统。当白...快速射电暴(Fast Radio Bursts,FRBs)是来自河外的短暂而明亮的射电能量脉冲,有重复快速射电暴和非重复快速射电暴两种类型。重复快速射电暴的重复爆发行为可能源于一个具有强偶极磁场的中子星和磁化的白矮星组成的致密双星系统。当白矮星充满它的洛希瓣时,物质将通过内拉格朗日点转移到中子星表面。一次爆发之后,白矮星可能被踢开,在演化过程中再次吸积,实现重复爆发现象。根据重复射电暴FRB 121102和FRB 180916重复爆发的观测数据,研究了白矮星-中子星的双星模型中两次爆发的时间间隔和两次爆发中前次爆发的流量之间的关系,通过理论值和观测值的比较,肯定了这样一个间歇的洛希瓣外流机制可能解释重复快速射电暴的重复爆发行为。展开更多
文摘在椭圆轨道的致密双星模型作为周期性重复快速射电暴(Fast Radio Bursts,FRBs)起源的基础上,考虑引力辐射对快速射电暴周期性行为的影响。这个双星系统包含一个具有强偶极磁场的中子星和一个磁化的白矮星。当白矮星充满它的洛希瓣时,物质将通过内拉格朗日点转移到中子星表面。由于角动量守恒,白矮星可能在一次爆发之后被踢开,接着在演化过程中由于引力辐射再次充满洛希瓣,实现再次爆发。这种情况下,快速射电暴的周期对应于双星轨道周期P_(orb),而它与两次质量转移时间间隔Δt之间的关系是能否显现周期性行为的关键因素。很明显,Δt≈P_(orb)或者Δt<P_(orb)是周期性行为显现的必要条件。反之,如果Δt>>P_(orb),周期性将很难观测到。结果表明,只有相对较长周期的快速射电暴才能显示周期性行为,这表明目前仅有的两个周期性快速射电暴都对应于较长的周期是合理的。
文摘ASTEROSEISMOLOGY of pulsating white dwarfs is an effective tool for us to infer their internal structures and the activities of stars on the final stages of stellar evolution. DA-type pulsating white dwarfs, with hydrogen-rich shells and low temperatures, constitute an instability strip in the H-R diagram, which have only 24 members. In order to push forward the research work in this field, many astronomers have devoted themselves to the search of new possible members for a long time. During two nights on February of 1996, the authors observed five candidates selected from the Kiso survey (Noguchi et al., 1980; Kondo et al., 1984), with the 1.93-m telescope at Observatoire de Haute-Provence, France. In the present note, we report the discovery of two new variables from this observation run: KUV 08368+4026 and KUV 11370+4222.
文摘Using the linearized relativistic Vlasov-Maxwell equations,a generalized expression for the plasma conductivity tensor is derived.The dispersion relation for the O-mode in a relativistic degenerate electron plasma is investigated by employing the Fermi-Dirac distribution function.The propagation characteristics of the O-mode（cut offs,resonances,propagation regimes,harmonic structure） are examined by using specific values of the density and the magnetic field that correspond to different relativistic dense environments.Further,it is observed that due to the relativistic effects the cut off and the resonance points are shifted to low frequency values,as a result the propagation regime is reduced.The dispersion relations for the non-relativistic and the ultra-relativistic limits are also presented.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.10947023,11275073,and 11305063)the Fundamental Research Funds for the Central University of China(Grant Nos.2014ZG0036 and 2013ZM107)sponsored by the Science Research Foundation for Returned Overseas Chinese Scholars,SEM,and has made use of NASA’s Astrophysics Data System
文摘Recently, U. Das and B. Mukhopadhyay proposed that the Chandrasekhar limit of a white dwarf could reach a new high level （2.58M） if a superstrong magnetic field were considered （Das U and Mukhopadhyay B 2013 Phys. Rev. Lett. 110 071102）, where the structure of the strongly magnetized white dwarf （SMWD） is calculated in the framework of Newtonian theory （NT）. As the SMWD has a far smaller size, in contrast with the usual expectation, we found that there is an obvious general relativistic effect （GRE） in the SMWD. For example, for the SMWD with a one Landau level system, the super-Chandrasekhar mass limit in general relativity （GR） is approximately 16.5% lower than that in NT. More interestingly, the maximal mass of the white dwarf will be first increased when the magnetic field strength keeps on increasing and reaches the maximal value M = 2.48MQ with BD = 391.5. Then if we further increase the magnetic fields, surprisingly, the maximal mass of the white dwarf will decrease when one takes the GRE into account.
文摘Using a program written in Excel, it was found that a supernova remnant, with a mass between 1.44 and 2 solar masses, contracts down to a neutron star. During the collapse, the decreasing gravitational potential slows time. Here, the pressure becomes high enough to stop the contraction. At greater than 2.2 solar masses, while the remnant is still contracting, the gravitational potential causes time to relatively freeze at the center, and stop the contraction before the pressure gets high enough to stop it, as it did in a neutron star. This also freezes the flow of information concerning the decrease in gravitational potential, thus, the frozen portions remain frozen and do not contract down any further and become imaginary. On top of this frozen center, additional matter physically and relatively contracts and the radius of the freeze point moves out. If the freeze made its way to the surface, it would meet the condition of a black hole, having a Schwarzschild radius;but it does not quite get there. The surface is not quite frozen. Even though these “almost black holes” do not have an event horizon, they are almost as small as that described by the Schwarzschild radius and due to the gravitational red shift, are very hard to see. A black star has been created. A contracting white dwarf at the Chandrasekhar limit (1.44 solar masses) has a density of about 1 × 109 kg/m3. After it cools and then collapses into a neutron star, it will have a minimum density of 3.5 × 1015 kg/m3 near the surface. This article explains how these two densities relate to why there are no supernova created stellar black stars above 15 solar masses and why super massive black stars start at 50,000 solar masses? Extracting limits like these cannot be accomplished using the standard black hole model, but this black star model has revealed these size limits and a lot more.
文摘Fast radio bursts (FRBs) at cosmological distances still hold concealed physical origins. Previously Liu (2018) proposes a scenario that the collision between a neutron star (NS) and a white dwarf (WD) can be one of the progenitors of non-repeating FRBs and notices that the repeating FRBs can also be explained if a magnetar formed after such NS-WD merger. In this paper, we investigate this channel of magnetar formation in more detail. We propose that the NS-WD post-merger, after cooling and angular momentum redistribution, may collapse to either a black hole or a new NS or even remains as a hybrid WDNS, depending on the total mass of the NS and WD. In particular, the newly formed NS can be a magnetar if the core of the WD collapsed into the NS while large quantities of degenerate electrons of the WD compressed to the outer layers of the new NS. A strong magnetic field can be formed by the electrons and positive charges with different angular velocities induced by the differential rotation of the newborn magnetar. Such a magnetar can power the repeating FRBs by the magnetic reconnections due to the crustal movements or starquakes.
文摘快速射电暴(Fast Radio Bursts,FRBs)是来自河外的短暂而明亮的射电能量脉冲,有重复快速射电暴和非重复快速射电暴两种类型。重复快速射电暴的重复爆发行为可能源于一个具有强偶极磁场的中子星和磁化的白矮星组成的致密双星系统。当白矮星充满它的洛希瓣时,物质将通过内拉格朗日点转移到中子星表面。一次爆发之后,白矮星可能被踢开,在演化过程中再次吸积,实现重复爆发现象。根据重复射电暴FRB 121102和FRB 180916重复爆发的观测数据,研究了白矮星-中子星的双星模型中两次爆发的时间间隔和两次爆发中前次爆发的流量之间的关系,通过理论值和观测值的比较,肯定了这样一个间歇的洛希瓣外流机制可能解释重复快速射电暴的重复爆发行为。
