LIGO-Virgo has observed the gravitational waves(GWs)from the coalescence of binary black hole(BBH)and binary neutron star(BNS)during O1 and O2,and the ones from NS-BH are expected to be hunted in the operating O3 run....LIGO-Virgo has observed the gravitational waves(GWs)from the coalescence of binary black hole(BBH)and binary neutron star(BNS)during O1 and O2,and the ones from NS-BH are expected to be hunted in the operating O3 run.The population properties and mass distribution of NS-BH mergers are poorly understood now,thus researchers simulated their chirp mass(M)distribution by a synthetic model,in which the BHs and NSs were inferred by LIGO-Virgo(O1/O2),and obtained the values in the range of 2.1 M_(⊙)<M<7.3 M_(⊙).In this paper,we further simulate the GW frequency(fGW)distribution of NS-BH mergers by the above-stated synthetic model,with a basic binary system model through the Monte Carlo method.Our results predict that the median with 90%credible intervals is 165+475-64 Hz in the case of Schwarzschild BH when the system just before merger,and this GW frequency is expected to increase several times in the merger stage,which is lying in the frequency band of LIGO-Virgo,i.e.,about 15 Hz to a few kHz.Our results provide an important reference for hunting the NS-BH mergers by the on-going O3 run of LIGO-Virgo.展开更多
In a second-order r-mode theory, Sa and Tome found that the r-mode oscillation in neutron stars （NSs） could induce stellar differential rotation, which naturally leads to a saturated state of the oscillation. Based ...In a second-order r-mode theory, Sa and Tome found that the r-mode oscillation in neutron stars （NSs） could induce stellar differential rotation, which naturally leads to a saturated state of the oscillation. Based on a consideration of the coupling of the r-modes and the stellar spin and thermal evolution, we carefully investigate the influences of the differential rotation on the long-term evolution of isolated NSs and NSs in low-mass X-ray binaries, where the viscous damping of the r-modes and its resultant effects are taken into account. The numerical results show that, for both kinds of NSs, the differential rotation can significantly prolong the duration of the r-modes. As a result, the stars can keep nearly a constant temperature and constant angular velocity for over a thousand years. Moreover, the persistent radiation of a quasi-monochromatic gravitational wave would also be predicted due to the long-term steady r-mode oscillation and stellar rotation. This increases the detectability of gravitational waves from both young isolated and old accreting NSs.展开更多
Large ground-based laser beam interferometers are presently in operation both in the USA （LIGO） and in Europe （VIRGO） and potential sources that might be detected by these instruments are revisited. The present ge...Large ground-based laser beam interferometers are presently in operation both in the USA （LIGO） and in Europe （VIRGO） and potential sources that might be detected by these instruments are revisited. The present generation of detectors does not have a sensitivity high enough to probe a significant volume of the universe and, consequently, predicted event rates are very low. The planned advanced generation of interferometers will probably be able to detect, for the first time, a gravitational sig- nal. Advanced LIGO and EGO instruments are expected to detect few （some）： binary coalescences consisting of either two neutron stars, two black holes or a neutron star and a black hole. In space, the sensitivity of the planned LISA spacecraft constellation will allow the detection of the gravitational signals, even within a ＂pessimistic＂ range of possible signals, produced during the capture of compact objects by supermassive black holes, at a rate of a few tens per year.展开更多
The currently well-developed models for equations of state （EoSs） have been severely impacted by recent measurements of neutron stars with a small radius and/or large mass. To explain these measurements, the theory ...The currently well-developed models for equations of state （EoSs） have been severely impacted by recent measurements of neutron stars with a small radius and/or large mass. To explain these measurements, the theory of gravitational field shielding by a scalar field is applied. This theory was recently developed in accor- dance with the five-dimensional （5D） fully covariant Kaluza-Klein （KK） theory that has successfully unified Einstein＇s general relativity and Maxwell＇s electromagnetic theory. It is shown that a massive, compact neutron star can generate a strong scalar field, which can significantly shield or reduce its gravitational field, thus making it more massive and more compact. The mass-radius relation developed under this type of modified gravity can be consistent with these recent measurements of neutron stars. In addition, the effect of gravitational field shielding helps explain why the supernova explosions of some very massive stars （e.g.9 40 MQ as measured recently） actually formed neutron stars rather than black holes as expected. The EoS models, ruled out by measurements of small radius and/or large mass neutron stars according to the the- ory of general relativity, can still work well in terms of the 5D fully covariant KK theory with a scalar field.展开更多
A stochastic background of gravitational waves with astrophysical origins may have＇resulted from the superposition of a large number of unresolved sources since the beginning of stellar activity. Its detection would ...A stochastic background of gravitational waves with astrophysical origins may have＇resulted from the superposition of a large number of unresolved sources since the beginning of stellar activity. Its detection would put very strong constraints on the physical properties of compact objects, the initial mass function and star for- marion history. On the other hand, it could be a ＇noise＇ that would mask the stochastic background of its cosmological origin. We review the main astrophysical processes which are able to produce a stochastic background and discuss how they may differ from the primordial contribution in terms of statistical properties. Current detection methods are also presented.展开更多
Gravitational waves have been detected in the past few years from several transient events such as merging stellar mass black holes, binary neutron stars, etc. These waves have frequencies in a band ranging from a few...Gravitational waves have been detected in the past few years from several transient events such as merging stellar mass black holes, binary neutron stars, etc. These waves have frequencies in a band ranging from a few hundred hertz to around a kilohertz to which LIGO type instruments are sensitive. LISA would be sensitive to much lower range of frequencies from SMBH mergers. Apart from these cataclysmic burst events, there are innumerable sources of radiation which are continuously emitting gravitational waves of all frequencies. These include a whole mass range of compact binary and isolated compact objects as well as close planetary stellar entities. In this work, quantitative estimates are made of the gravitational wave background produced in typical frequency ranges from such sources emitting over a Hubble time and the fluctuations in the <i>h</i> values measured in the usual devices. Also estimates are made of the high frequency thermal background gravitational radiation from hot stellar interiors and newly formed compact objects.展开更多
The state of supranuclear matter in compact stars remains puzzling, and it is argued that pul- sars could be strangeon stars. What would happen if binary strangeon stars merge？ This kind of merger could result in the...The state of supranuclear matter in compact stars remains puzzling, and it is argued that pul- sars could be strangeon stars. What would happen if binary strangeon stars merge？ This kind of merger could result in the formation of a hyper-massive strangeon star, accompanied by bursts of gravitational waves and electromagnetic radiation （and even a strangeon kilonova explained in the paper）. The tidal polarizability of binary strangeon stars is different from that of binary neutron stars, because a strangeon star is self-bound on the surface by the fundamental strong force while a neutron star by the gravity, and their equations of state are different. Our calculation shows that the tidal polarizability of merging bi- nary strangeon stars is favored by GW170817. Three kinds of kilonovae （i.e., of neutron, quark and strangeon） are discussed, and the light curve of the kilonova AT 2017gfo following GW170817 could be explained by considering the decaying strangeon nuggets and remnant star spin-down. Additionally, the energy ejected to the fireball around the nascent remnant strangeon star, being manifested as a gamma-ray burst, is calculated. It is found that, after a prompt burst, an X-ray plateau could follow in a timescale of 102 - 103 s. Certainly, the results could be tested also by further observational synergies between gravitational wave detectors （e.g., Advanced LIGO） and X-ray telescopes （e.g., the Chinese HXMT satellite and eXTP mission）, and especially if the detected gravitational wave form is checked by peculiar equations of state provided by the numerical relativistical simulation.展开更多
This paper is devoted to discussing the difference in the thermodynamic entropy budget per baryon in each type of stellar object found in the Universe. We track and discuss the actual decrease of the stored baryonic t...This paper is devoted to discussing the difference in the thermodynamic entropy budget per baryon in each type of stellar object found in the Universe. We track and discuss the actual decrease of the stored baryonic thermodynamic entropy from the most primitive molecular cloud up to the final fate of matter in black holes, passing through evolved states of matter as found in white dwarfs and neutron stars. We then discuss the case of actual stars with different masses throughout their evolution, clarifying the role of the virial equilibrium condition for the decrease in entropy and related issues. Finally, we discuss the role of gravity in driving the composition and the structural changes of stars with different Main Sequence masses during their evolution up to the final product. Particularly, we discuss the entropy of a black hole in this context arguing that the dramatic increase in its entropy, differently from the other cases, is due to the gravitational field itself.展开更多
We have studied X-ray spectral state transitions that can be seen in the long- term monitoring light curves of bright X-ray binaries from the All-Sky Monitor （ASM） onboard the Rossi X-ray Timing Explorer （RXTE） an...We have studied X-ray spectral state transitions that can be seen in the long- term monitoring light curves of bright X-ray binaries from the All-Sky Monitor （ASM） onboard the Rossi X-ray Timing Explorer （RXTE） and the Burst Alert Telescope （BAT） onboard Swift during a period of five years from 2005 to 2010. We have applied a program to automatically identify the hard-to-soft （H-S） spectral state transitions in the bright X-ray binaries monitored by the ASM and the BAT. In total, we identified 128 hard-to-soft transitions, of which 59 occurred after 2008. We also determined the transition fluxes and the peak fluxes of the following soft states, updated the measurements of the luminosity corresponding to the H-S transition and the peak luminosity of the following soft state in about 30 bright persistent and transient black hole and neutron star binaries following Yu ＆Yan, and found the luminosity correlation and the luminosity range of spectral transitions in data between 2008-2010 are about the same as those derived from data before 2008. This further strengthens the idea that the luminosity at which the H-S spectral transition occurs in the Galactic X-ray binaries is determined by non-stationary accretion parameters such as the rate-of-change of the mass accretion rate rather than the mass accretion rate itself. The correlation is also found to hold in data of individual sources 4U 1608-52 and 4U 1636-53.展开更多
LIGO/Virgo S190814 bv is the first high-probability neutron star–black hole(NSBH)merger candidate,whose gravitational waves(GWs)triggered LIGO/Virgo detectors at21:10:39.012957 UT,14 August 2019.It has a probability&...LIGO/Virgo S190814 bv is the first high-probability neutron star–black hole(NSBH)merger candidate,whose gravitational waves(GWs)triggered LIGO/Virgo detectors at21:10:39.012957 UT,14 August 2019.It has a probability>99%of being an NSBH merger,with a low false alarm rate(FAR)of one per 1.559 e+25 years.For an NSBH merger,electromagnetic counterparts(especially short gamma-ray bursts(GRBs))are generally expected.However,no electromagnetic counterpart has been found in the extensive follow-up observing campaign.In the present work,we propose a novel explanation for this null result.In our scenario,LIGO/Virgo S190814 bv is just a GW mirror image of the real NSBH merger which should have been detected before 14 September 2015,but at that time we had no ability to detect its GW signals.The electromagnetic counterparts associated with the real NSBH merger should be found in the archive data before 14 September 2015.In this work,we indeed find nine short GRBs that are possibly electromagnetic counterparts.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11988101,11773005,U2031203,U1631236,11703001,U1731238,U1938117,11725313,and 11721303)the International Partnership Program of Chinese Academy of Sciences(Grant No.114A11KYSB20160008)+1 种基金the National Key R&D Program of China(Grant No.2016YFA0400702)the Subsidy Project of the National Natural Science Foundation of China(Grant No.2021GZJ006)。
文摘LIGO-Virgo has observed the gravitational waves(GWs)from the coalescence of binary black hole(BBH)and binary neutron star(BNS)during O1 and O2,and the ones from NS-BH are expected to be hunted in the operating O3 run.The population properties and mass distribution of NS-BH mergers are poorly understood now,thus researchers simulated their chirp mass(M)distribution by a synthetic model,in which the BHs and NSs were inferred by LIGO-Virgo(O1/O2),and obtained the values in the range of 2.1 M_(⊙)<M<7.3 M_(⊙).In this paper,we further simulate the GW frequency(fGW)distribution of NS-BH mergers by the above-stated synthetic model,with a basic binary system model through the Monte Carlo method.Our results predict that the median with 90%credible intervals is 165+475-64 Hz in the case of Schwarzschild BH when the system just before merger,and this GW frequency is expected to increase several times in the merger stage,which is lying in the frequency band of LIGO-Virgo,i.e.,about 15 Hz to a few kHz.Our results provide an important reference for hunting the NS-BH mergers by the on-going O3 run of LIGO-Virgo.
基金Supported by the National Natural Science Foundation of China(Grant Nos.10603002 and 10773004)
文摘In a second-order r-mode theory, Sa and Tome found that the r-mode oscillation in neutron stars （NSs） could induce stellar differential rotation, which naturally leads to a saturated state of the oscillation. Based on a consideration of the coupling of the r-modes and the stellar spin and thermal evolution, we carefully investigate the influences of the differential rotation on the long-term evolution of isolated NSs and NSs in low-mass X-ray binaries, where the viscous damping of the r-modes and its resultant effects are taken into account. The numerical results show that, for both kinds of NSs, the differential rotation can significantly prolong the duration of the r-modes. As a result, the stars can keep nearly a constant temperature and constant angular velocity for over a thousand years. Moreover, the persistent radiation of a quasi-monochromatic gravitational wave would also be predicted due to the long-term steady r-mode oscillation and stellar rotation. This increases the detectability of gravitational waves from both young isolated and old accreting NSs.
文摘Large ground-based laser beam interferometers are presently in operation both in the USA （LIGO） and in Europe （VIRGO） and potential sources that might be detected by these instruments are revisited. The present generation of detectors does not have a sensitivity high enough to probe a significant volume of the universe and, consequently, predicted event rates are very low. The planned advanced generation of interferometers will probably be able to detect, for the first time, a gravitational sig- nal. Advanced LIGO and EGO instruments are expected to detect few （some）： binary coalescences consisting of either two neutron stars, two black holes or a neutron star and a black hole. In space, the sensitivity of the planned LISA spacecraft constellation will allow the detection of the gravitational signals, even within a ＂pessimistic＂ range of possible signals, produced during the capture of compact objects by supermassive black holes, at a rate of a few tens per year.
基金supported by NASA EPSCoR(NNX07AL52A)NSF CISMand REU,the Alabama A&M University(AAMU)Title Ⅲ programsthe National Natural Science Foundation of China(Grant No.40890161)
文摘The currently well-developed models for equations of state （EoSs） have been severely impacted by recent measurements of neutron stars with a small radius and/or large mass. To explain these measurements, the theory of gravitational field shielding by a scalar field is applied. This theory was recently developed in accor- dance with the five-dimensional （5D） fully covariant Kaluza-Klein （KK） theory that has successfully unified Einstein＇s general relativity and Maxwell＇s electromagnetic theory. It is shown that a massive, compact neutron star can generate a strong scalar field, which can significantly shield or reduce its gravitational field, thus making it more massive and more compact. The mass-radius relation developed under this type of modified gravity can be consistent with these recent measurements of neutron stars. In addition, the effect of gravitational field shielding helps explain why the supernova explosions of some very massive stars （e.g.9 40 MQ as measured recently） actually formed neutron stars rather than black holes as expected. The EoS models, ruled out by measurements of small radius and/or large mass neutron stars according to the the- ory of general relativity, can still work well in terms of the 5D fully covariant KK theory with a scalar field.
文摘A stochastic background of gravitational waves with astrophysical origins may have＇resulted from the superposition of a large number of unresolved sources since the beginning of stellar activity. Its detection would put very strong constraints on the physical properties of compact objects, the initial mass function and star for- marion history. On the other hand, it could be a ＇noise＇ that would mask the stochastic background of its cosmological origin. We review the main astrophysical processes which are able to produce a stochastic background and discuss how they may differ from the primordial contribution in terms of statistical properties. Current detection methods are also presented.
文摘Gravitational waves have been detected in the past few years from several transient events such as merging stellar mass black holes, binary neutron stars, etc. These waves have frequencies in a band ranging from a few hundred hertz to around a kilohertz to which LIGO type instruments are sensitive. LISA would be sensitive to much lower range of frequencies from SMBH mergers. Apart from these cataclysmic burst events, there are innumerable sources of radiation which are continuously emitting gravitational waves of all frequencies. These include a whole mass range of compact binary and isolated compact objects as well as close planetary stellar entities. In this work, quantitative estimates are made of the gravitational wave background produced in typical frequency ranges from such sources emitting over a Hubble time and the fluctuations in the <i>h</i> values measured in the usual devices. Also estimates are made of the high frequency thermal background gravitational radiation from hot stellar interiors and newly formed compact objects.
基金supported by the National Key R&D Program of China(No.2017YFA0402602)the West Light Foundation(XBBS-2014-23)the National Natural Science Foundation of China(Grant Nos.11203018,11673002 and U1531243)
文摘The state of supranuclear matter in compact stars remains puzzling, and it is argued that pul- sars could be strangeon stars. What would happen if binary strangeon stars merge？ This kind of merger could result in the formation of a hyper-massive strangeon star, accompanied by bursts of gravitational waves and electromagnetic radiation （and even a strangeon kilonova explained in the paper）. The tidal polarizability of binary strangeon stars is different from that of binary neutron stars, because a strangeon star is self-bound on the surface by the fundamental strong force while a neutron star by the gravity, and their equations of state are different. Our calculation shows that the tidal polarizability of merging bi- nary strangeon stars is favored by GW170817. Three kinds of kilonovae （i.e., of neutron, quark and strangeon） are discussed, and the light curve of the kilonova AT 2017gfo following GW170817 could be explained by considering the decaying strangeon nuggets and remnant star spin-down. Additionally, the energy ejected to the fireball around the nascent remnant strangeon star, being manifested as a gamma-ray burst, is calculated. It is found that, after a prompt burst, an X-ray plateau could follow in a timescale of 102 - 103 s. Certainly, the results could be tested also by further observational synergies between gravitational wave detectors （e.g., Advanced LIGO） and X-ray telescopes （e.g., the Chinese HXMT satellite and eXTP mission）, and especially if the detected gravitational wave form is checked by peculiar equations of state provided by the numerical relativistical simulation.
基金the financial support from the Fundao de AmparoàPesquisa do Estado de So Paulothe CNPq Agency(Brazil)for partial financial support
文摘This paper is devoted to discussing the difference in the thermodynamic entropy budget per baryon in each type of stellar object found in the Universe. We track and discuss the actual decrease of the stored baryonic thermodynamic entropy from the most primitive molecular cloud up to the final fate of matter in black holes, passing through evolved states of matter as found in white dwarfs and neutron stars. We then discuss the case of actual stars with different masses throughout their evolution, clarifying the role of the virial equilibrium condition for the decrease in entropy and related issues. Finally, we discuss the role of gravity in driving the composition and the structural changes of stars with different Main Sequence masses during their evolution up to the final product. Particularly, we discuss the entropy of a black hole in this context arguing that the dramatic increase in its entropy, differently from the other cases, is due to the gravitational field itself.
基金supported in part by the National Natural Science Foundation of China (Grant Nos. 0773023,10833002 and 11073043)the One Hundred Talents project of the Chinese Academy of Sciences+3 种基金the Shanghai Pujiang Program (08PJ14111)the National Basic Research Program of China (973project 2009CB824800)the grant for concept study of space science from the Chinese Academy of Sciencethe starting funds at the Shanghai Astronomical Observatory
文摘We have studied X-ray spectral state transitions that can be seen in the long- term monitoring light curves of bright X-ray binaries from the All-Sky Monitor （ASM） onboard the Rossi X-ray Timing Explorer （RXTE） and the Burst Alert Telescope （BAT） onboard Swift during a period of five years from 2005 to 2010. We have applied a program to automatically identify the hard-to-soft （H-S） spectral state transitions in the bright X-ray binaries monitored by the ASM and the BAT. In total, we identified 128 hard-to-soft transitions, of which 59 occurred after 2008. We also determined the transition fluxes and the peak fluxes of the following soft states, updated the measurements of the luminosity corresponding to the H-S transition and the peak luminosity of the following soft state in about 30 bright persistent and transient black hole and neutron star binaries following Yu ＆Yan, and found the luminosity correlation and the luminosity range of spectral transitions in data between 2008-2010 are about the same as those derived from data before 2008. This further strengthens the idea that the luminosity at which the H-S spectral transition occurs in the Galactic X-ray binaries is determined by non-stationary accretion parameters such as the rate-of-change of the mass accretion rate rather than the mass accretion rate itself. The correlation is also found to hold in data of individual sources 4U 1608-52 and 4U 1636-53.
基金supported in part by NSFC under Grants No.11975046 and No.11575022。
文摘LIGO/Virgo S190814 bv is the first high-probability neutron star–black hole(NSBH)merger candidate,whose gravitational waves(GWs)triggered LIGO/Virgo detectors at21:10:39.012957 UT,14 August 2019.It has a probability>99%of being an NSBH merger,with a low false alarm rate(FAR)of one per 1.559 e+25 years.For an NSBH merger,electromagnetic counterparts(especially short gamma-ray bursts(GRBs))are generally expected.However,no electromagnetic counterpart has been found in the extensive follow-up observing campaign.In the present work,we propose a novel explanation for this null result.In our scenario,LIGO/Virgo S190814 bv is just a GW mirror image of the real NSBH merger which should have been detected before 14 September 2015,but at that time we had no ability to detect its GW signals.The electromagnetic counterparts associated with the real NSBH merger should be found in the archive data before 14 September 2015.In this work,we indeed find nine short GRBs that are possibly electromagnetic counterparts.
