渐近安全引力下的黑洞阴影和光环

重点讨论了薄盘吸积与渐近安全(asymptotically safe,AS)引力修正参数对黑洞阴影和光环的影响.对于薄盘吸积,黑洞的暗区就是黑洞的阴影,而明亮的光环则是由直接像、透镜环和光子环组成的.对于吸积盘辐射源比强度,考虑了3个不同辐射轮廓模型.对辐射起始于最内圆轨道的二阶衰减函数模型,直接像、透镜环和光子环可以明显区分.直接像对黑洞光环亮度贡献最大,透镜环对光环亮度贡献很小,而光子环的贡献几乎可以忽略,且对应观测强度的峰值随AS引力参数的增加而减小,即对应光环亮度随修正参数的增大而变暗.对于辐射起始于光子球半径的三阶衰减函数模型,透镜环和光子环叠加在直接像上,使观测强度出现新的极值.这一极值随AS引力修正参数的增加而增加,且使得黑洞光环的亮度更亮.对辐射起始于事件视界的反三角衰减函数模型,透镜环和光子环在直接像上的叠加范围更大,观测到的光环更宽,且AS引力参数值越小,透镜环和光子环越难区分,黑洞光环的亮度越大.总之,研究表明,黑洞阴影半径的大小随AS修正参数的增加而减小,对于不同的AS引力修正参数,辐射源光强度、尤其是观测强度的辐射轮廓存在显著差异,导致黑洞的阴影和亮环明显不同.

带有整体单极的Reissner-Nordstrom-AdS黑洞在扩展相空间中的霍金辐射

本文研究了带有整体单极的Reissner-Nordstrom-AdS黑洞在扩展相空间中出射粒子的量子隧穿辐射过程.其中,将宇宙学参数视为动态变量而不同于之前研究工作中将其视为常数而忽略其贡献.具体地,在计算出射粒子隧穿率时将宇宙学参数引入计算并将其解释为热力学压强.计算结果表明,出射粒子的隧穿率与粒子出射前后黑洞的贝肯斯坦-霍金熵差成正比,辐射谱偏离了纯热谱,该结果与将宇宙学参数视为常数的情况完全相同.这意味着在扩展相空间中可以得到粒子的隧穿概率,并且隧穿过程不依赖于热力学状参量,这一工作自然地进一步将霍金辐射推广到了带有整体单极Reissner-Nordstrom-AdS黑洞扩展相空间中.结果表明,整体单极子尽管影响粒子的动力学行为和热力学量,但并不影响熵变和隧穿率.

Study of Type-B QPOs Observed in Black Hole X-Ray Binary Swift J1728.9-3613

We report the detection of type-B quasi-periodic oscillation(QPO)of the black hole X-ray binary Swift J1728.9-3613 observed by NICER during the 2019 outburst.A type-B QPO was observed for the first two days and it disappeared as flux increased,but again appeared at∼7.70 Hz when flux was dramatically decreased.The source was found in the soft intermediate state during these observations.We further studied the energy dependence of the QPO.We found that QPO was observed only for a higher energy range implying that the origin of QPO is possibly due to the corona emitting higher energy photons by the inverse Compton process.The variation of spectral parameters can be explained with the disk truncation model.The fractional rms was found to be monotonically increased with energy.The phase lag spectrum followed the“U-shaped”curve.The rms and phase lag spectrum are modeled and explained with the single-component Comptonization model vkompthdk.

View of thermodynamic phase transition of the charged Gauss-Bonnet AdS black hole via the shadow

We examine thermodynamic phase transition(PT)of the charged Gauss-Bonnet Ad S black hole(BH)by utilizing the shadow radius.In this system,we rescale the corresponding Gauss-Bonnet coefficientαby a factor of 1/(D-4),and ensure thatαis positive to avoid any singularity problems.The equation derived for the shadow radius indicates that it increases as the event horizon radius increases,making it an independent variable for determining BH temperature.By investigating the PT curve in relation to shadows,we can observe that the shadow radius can be used as an alternative to the event horizon radius in explaining the phenomenon of BH PT.Furthermore,the results indicate that an increase in the parameterαcorresponds to a decrease in the temperature of the BH.By utilizing the relationship between the temperature and the shadow radius,it is possible to obtain the thermal profile of the Gauss-Bonnet AdS BH.It is evident that there is an N-type variation in temperature for pressures P<P_(c).Additionally,as the parameterαincreases,the region covered by shadow expands while the temperature decreases.The utilization of BH shadows as a probe holds immense significance in gaining a deeper understanding of BH thermodynamic behavior.

磁荷对Hayward-Anti-de Sitter黑洞的全息互信息的影响

Hayward黑洞是爱因斯坦引力非线性耦合一个携带磁荷的电磁场的解析解,是非线性磁单极子引力场的简并结构。一般情况下,黑洞的内部会存在奇点,而“非奇异”黑洞是一种内部没有奇点的黑洞。Hayward黑洞属于非奇异黑洞,此规则黑洞的对称性由磁势决定,带磁荷和不带磁荷的黑洞具有不同的微观结构。利用纠缠熵讨论磁荷对非奇异Hayward-Anti-de Sitter黑洞中全息互信息的影响。结果表明,随着条带宽度(子区域)的增加,2个渐进子系统纠缠增大,且全息互信息随磁荷的增加而降低。除此之外,存在临界磁荷使得全息互信息为零,此时对偶的子区域之间不存在纠缠,磁荷取不同值时,全息互信息消失的条带宽度临界值是不同的。

关于黑洞和时间性质的探索

简单回顾了北京师范大学广义相对论团队创建初期的历史.介绍了团队独创的部分研究成果:一项是创建了逐点计算非稳态黑洞表面各点温度的方法;另一项是指出热力学第零定律等价于钟速同步的传递性.

类比Banados-Teitelboim-Zanelli黑洞的辐射屏蔽

虽然类比引力理论表明可以使用实验室的物理系统类比黑洞的时空结构,但是旋转黑洞的结构很难在实验室体系中找到较好的对应.本文使用特设的涡旋光,在理论上找到了一种接近Banados-Teitelboim-Zanelli(BTZ)黑洞的类比结构,通过计算无质量粒子和声波在类比BTZ黑洞和引力的BTZ黑洞时空中的运动来比较它们的异同.两种黑洞时空无质量粒子和声波的有效势能给出了相同的能量和角动量的辐射禁区分布,不同的是, BTZ黑洞经典禁区沿径向将趋近固定的能量值,而类比BTZ黑洞的经典禁区沿径向将闭合.幸运的是,在视界和能层附近,无质量粒子和声波的运动行为几乎一致,从这个角度来说,类比实验体系能够很好地模拟BTZ黑洞.特别地,在两种黑洞时空下,低能量高角动量的粒子的经典禁区都更宽.

恒星级双黑洞自旋研究进展

自2015年以来,人们已经探测到93例恒星级双黑洞并合引力波事件,测量了双黑洞质量、自旋和距离等参数,并获得了其统计分布。不同双黑洞起源机制产生的双黑洞性质分布,特别是自旋分布,会显著不同,其可用来限制双黑洞起源。简单回顾了双星演化和动力学相互作用等双黑洞形成机制及自旋来源;综述了利用自旋限制双黑洞起源的一般方法和常见模型,以及利用LIGO/Virgo引力波数据取得的相关进展,并对未来发展前景进行了展望。

Does Diffuse Circumnuclear Gas around Sgr A^(*) Achieve Collisional Ionization Equilibrium or Remain Non-equilibrium Ionization?

The feeding and feedback processes at the vicinity of a supermassive black hole(BH)are essential for our understanding of the connection between supermassive BH and its host galaxy.In this work,we provide a detailed investigation,both observational and theoretical,on the diffuse(~2"-20",~0.08-0.8 pc)X-ray emission around Sgr A*.Over two-decade Chandra observations are gathered to obtain highest signal-to-noise to date.We find that,the line center of iron lines of the outer 8"-18"region,ε_(c)=6.65+0.02-0.03 keV,is comparable to that(ε_(c)=6.60+0.05-0.03 keV)of the inner 2"-5"region.This is somewhat unexpected,since the gas temperature decreases further away from the central BH.Based on a dynamical inflow-outflow model that considers the gas feeding by stellar winds from Wolf-Rayet stars,we calculate the X-ray spectrum based on both the conventional collisional ionization equilibrium(CIE)assumption,and the newly developed non-equilibrium ionization(NEI)assumption.We find that,theoretically gases within~8"-10"remain in a CIE state,outside of this radius they will be in the NEI state.A comparison of the properties of~6.6 keV iron lines between CIE and NEI is addressed.Interestingly,the NEI interpretation of outer region is supported by the Chandra line center ε_(c) measurements of this region.

Mass Distribution of Black Holes with Effects of Convective Carbon Shell Burning on Pair-instability Pulsation and Fe Core Collapse

Motivated by the determination of black hole masses with gravitational-wave observations,we calculate the evolution of massive stars through presupernova stages and obtain the mass distribution of black holes.In the first part,we calculate the evolution of He stars with masses of 30-120 M_(⊙).We study in detail how convective carbon shell burning controls pair-instability pulsations before and during oxygen burning and determine their final fates.In the second part,we calculate the evolution of H-rich stars with initial masses of 13-80 M_(⊙) until Fe core collapse and obtain the possible black hole mass range by applying the criterion of the compactness parameters.From these models,we predict the mass distribution of black holes for stars that undergo Fe core collapse and pair-instability pulsation.The predicted masses for black holes range from 4.2 to 46 M_(⊙),which are consistent with the gravitational-wave observations.

黑洞双星的B型QPO频率与幂律通量的相关性的解释

观测表明,黑洞双星的B型准周期振荡(Quasi-Periodic Oscillation,QPO)频率与幂律通量之间存在正相关性.试图基于阿尔文波振荡模型定量解释该相关性.标准薄吸积盘辐射通量极大值处的阿尔文波振荡产生QPO.标准薄盘上的软光子与冕或喷流基部的热电子介质发生逆康普顿散射产生幂律通量.通过吸积率的连续变化,得到QPO频率与幂律通量关系的分析解和数值解.模拟得到的相关性在合理的参数范围内与观测值相吻合.QPO频率与幂律通量的正相关性可以理解为,较强的磁场导致较高的阿尔文波频率和较高的电子温度从而得到较高的幂律通量.结果表明B型QPO可能与吸积盘或喷流中的环向磁场的活动有关.

The Reissner-Nordström black hole surrounded by quintessence may not be destroyed

In the study of weak cosmic censorship conjectures(WCCC),some research finds that the Reissner-Nordström black hole might be destroyed by a test particle with particular mass and charge under some conditions,which means that the naked singularity of the black hole could be observed.This is not allowed in WCCC.We have never observed such naked singularities which should not exist in theory,so we need to find a proper way to protect the black hole from being destroyed by such particles.In this paper,we study a Reissner-Nordström black hole that is surrounded by quintessence(RN-Q)and find that the black hole would be stable and safe because of the effective potential barrier induced by the quintessence term.This result may also show in a sense that the quintessence might have more potential value.

Nonlinear Variability Observed with Insight-HXMT in MAXI J1820+070 and MAXI J1535-571

We present the timing analysis of the nonlinear variability in two black hole low mass X-ray binaries MAXI J1820+070 and MAXI J1535-571 by using the bicoherence,a measure of phase coupling at different Fourier frequencies.We found different patterns,e.g.,“cross”and“hypotenuse,”for LFQPOs in different outburst states.When they can be clearly distinguished,bicoherence patterns are similar over a wide energy range of 1–100 keV.It is intriguing that in some type-C QPOs we found the patterns that are normally observed in type-B QPOs.On the contrary,the“hypotenuse”pattern,a characteristic of type-C QPOs,was detected in a type-B QPO.This suggests that different types of QPOs may originate from similar underlying mechanisms.In addition,we speculate that the nonlinear variability may be a promising approach to disentangle distinct QPO models which assume different interactions between the broadband noise and QPO components.

NuSTAR View of the R-ΓCorrelation in the Hard State of Black Hole Lowmass X-Ray Binaries

The power law and reflection emission have been observed in the X-ray spectra of both black hole X-ray binaries(BHXRBs)and active galactic nuclei(AGNs),indicating a common physical origin of the X-ray emission from these two types of sources.The relevant parameters describing the shape of both components and the potential correlation between these parameters can provide important clues on the geometric and physical properties of the disk and the corona in these sources.In this work,we present a positive correlation between the photon indexΓand the reflection strength R for the low-mass BHXRBs in the hard state by modeling NuSTAR data,which is qualitatively consistent with the previous studies.We compare our results with the predictions from different theoretical disk-corona models.We show that the RIT correlation found in this work seems to favor the moving corona model proposed by Beloborodov.Our results indicate that the coronal geometry varies significantly among BHXRBs.We further compare our results with that of AGNs.We find that the reflection strength R is smaller than unity in the hard state of BHXRBs,while it can be as large as~5 in AGNs,which implies that the variations of the disk-coronal geometry of AGNs are more vigorous than that of the BHXRBs in the hard state.

The Spin Measurement of MAXI J0637-430:a Black Hole Candidate with High Disk Density

The Galactic black hole candidate MAXI J0637-430 was first discovered by MAXI/GSC on 2019 November 2.We study the spectral properties of MAXI J0637-430 by using the archived NuSTAR data and Swift/XRT data.After fitting the eight spectra by using a disk component and a powerlaw component model with absorption,we select the spectra with relatively strong reflection components for detailed X-ray reflection spectroscopy.Using the most state-of-art reflection model,relxillCp,the spectral fitting measures a black hole spin a_(*)>0.72 and the inclination angle of the accretion disk i=46.1_(-5.3)^(+4.0)degrees,at a 90%confidence level.In addition,the fitting results show an extreme supersolar iron abundance.Combined with the fitting results of reflection model reflionx_hd,we consider that this unphysical iron abundance may be caused by a very high-density accretion disk(n_(e)>2.34×10^(21)cm^(-3))or a strong Fe K_(α) emission line.The soft excess is found in the soft state spectral fitting results,which may be an extra free-free heating effect caused by high density of the accretion disk.Finally,we discuss the robustness of black hole spin obtained by X-ray reflection spectroscopy.The result of relatively high spin is self-consistent with broadened Fe K_(α) line.Iron abundance and disk density have no effect on the spin results.

The AGN Feedback in Compact Galaxies:On the Impact of a More Massive Central Black Hole

We conduct high-resolution hydrodynamical simulations using the MACER framework to investigate the interplay between the interstellar medium,active galactic nuclei(AGN)feedback and black hole(BH)feeding in a massive compact galaxy,with an emphasis on the impact of different central BH masses.We find that with a more massive central BH,high-speed outflows are more prominent,and the gas fraction in the compact galaxy is reduced.Due to the lower gas density and higher gas temperature,the compact galaxy with a more massive BH(MAS galaxy)remains predominantly single-phase with the cooling time t_(cool)■100t_(ff).In contrast,the compact galaxy with the reference BH mass(REF galaxy)maintains a higher gas fraction with a shorter cooling time,slightly more multiphase gas and less prominent outflows.We further demonstrate that the difference in gas thermal states and kinematics is caused by the stronger AGN feedback in the compact galaxy with a more massive BH,where the AGN wind power is twice as much as that with the reference BH.Since the AGN feedback efficiently suppresses the inflow rate and the BH feeding rate,the BH mass growth is significant in neither the compact galaxy with the reference BH nor that with the more massive BH,only by 24%and 11%of the initial BH mass,respectively,over the entire evolution time of 10 Gyr.We thus posit that without ex situ mass supply from mergers,the massive BHs in compact galaxies cannot grow significantly via gas accretion during the late phase,but might have already formed by the end of the rapid early phase of galaxy formation.

The Width-Flux Relation of the Broad Iron KαLine during the State Transitions of the Black Hole X-Ray Binaries

The observations of varying broad iron lines during the state transition of the black hole X-ray binaries have been accumulating.In this work,the relation between the normalized intensity and the width of iron lines is investigated,in order to understand better the variation of iron lines and possibly its connection to state transition.Considering the uncertainties due to ionization and illuminating X-rays,only the effects of geometry and gravity are taken into account.Three scenarios were studied,i.e.,the continuous disk model,the innermost annulus model,and the cloud model.As shown by our calculations,at given iron width,the line flux of the cloud model is smaller than that of the continuous disk model;while for the innermost annulus model,the width is almost unrelated with the flux.The range of the line strength depends on both the BH spin and the inclination of the disk.We then apply to the observation of MAXI J1631-479 by Nuclear Spectroscopic Telescope Array during its decay from the soft state to the intermediate state.We estimated the relative line strength and width according to the spectral fitting results in Xu et al.,and then compared with our theoretical width-flux relation.It was found that the cloud model was more favored.We further modeled the iron line profiles,and found that the cloud model can explain both the line profile and its variation with reasonable parameters.

SL(n,R)户田黑洞的隧穿效应

由于SL(n,R)户田黑洞具有很好的数学结构,是研究黑洞物理较为理想的场所.本文主要研究其黑洞的霍金辐射,以及相关信息丢失问题.为了简单,只考虑在四维静态球对称SL(n,R)户田黑洞下,通过计算静止质量为零的粒子在事件视界附近隧穿效应来研究霍金辐射.在粒子的隧穿过程中,利用能量守恒并考虑了隧穿粒子对背景时空的反作用.获得粒子通过事件视界的隧穿概率取决于粒子出射前后黑洞熵的变化,并在此基础上讨论了其信息丢失问题,在满足一定条件下,我们的结果与RN黑洞和施瓦茨黑洞的结果一致.

Shadow thermodynamics of AdS black hole with the nonlinear electrodynamics term

We creatively employ the shadow radius to study the thermodynamics of a charged Ad S black hole with a nonlinear electrodynamics(NLED)term.First,the connection between the shadow radius and event horizon is constructed with the aid of the geodesic analysis.It turns out that the black hole shadow radius shows a positive correlation as a function of the event horizon radius.Then in the shadow context,we find that the black hole temperature and heat capacity can be presented by the shadow radius.Further analysis shows that the shadow radius can work similarly to the event horizon in revealing black hole phase transition process.In this sense,we construct the thermal profile of the charged Ad S black hole with inclusion of the NLED effect.In the P<Pc case,it is found that the N-type trend of the temperature given by the shadow radius is always consistent with that obtained by using the event horizon.Thus,we can conclude for the charged Ad S black hole that the phase transition process can be intuitively presented as the thermal profile in the shadow context.Finally,the effects of NLED are carefully analyzed.

Analogue Black Holes in Reactive Molecules

We show that reactive molecules with a unit probability of reaction naturally provide a simulator of some intriguing black hole physics.The unit reaction at the short distance acts as an event horizon and delivers a one-way traffic for matter waves passing through the potential barrier when two molecules interact by high partialwave scatterings or dipole-dipole interactions.In particular,the scattering rate as a function of the incident energy exhibits a thermal-like distribution near the maximum of the interaction energy in the same manner as a scalar field scatters with the potential barrier outside the event horizon of a black hole.Such a thermal-like scattering can be extracted from the temperature-dependent two-body loss rate measured in experiments on KRb and other molecules.