分类： 天文学 >> 天文学 分类： 天文学 >> 天体物理学 分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 分类： 物理学 >> 地球物理学、天文学和天体物理学 提交时间： 2025-07-16
摘要： 提出黄氏度规，通过度规中的量子引力修正项：\frac{2kG_hM^2(\ln r+1)}{c^2 r}。统一计算黑洞视界与光子球，首次无需黑洞自旋参数（自旋实为观测后拟合）精准预言阴影直径。关键公式：黄氏度规视界方程：gtt=0： r_h = \frac{2GM}{c^2} + \frac{2kG_hM^2(\ln r_h +1)}{c^2}计算结果与观测验证：SgrA*（银河系中心黑洞）理论阴影直径43.41-53.96μas，EHT观测值51.8±7μas，覆盖误差带。M87*（M87星系中心黑洞）理论阴影直径38.63-46.71μas，EHT观测值42±3μas，完全覆盖。结论：1、终结自旋参数依赖：阴影直径仅由质量M和质量比k决定，无需假设黑洞自旋。2、量子引力可观测证据：对数修正项ln r是量子拓扑效应的直接体现，被EHT数据证实。3、解析取代观测拟合：所有结果通过解析计算得出，计算效率明显提升。
分类： 天文学 >> 天体物理学 提交时间： 2025-02-09
摘要： Inspired by the idea in Ref. [16], which introduced a viscosity coefficientinto the expansion equation describing the universe, we also attempt to introduce such a positive viscosity coefficientinto the rotational motion equation describing the galaxies, and then studies what will happen. Surprisingly, we obtained all the formulas assumed in MOND, including a concrete interpolation function between the centripetal acceleration and the Newtonian acceleration. But at the same time, something different from MOND was also obtained, that is, the critical acceleration, a0in MOND, does not need to be a constant, but increases with the mass of the galaxy increases, and under the action of viscosity coefficient, the rotational galaxies will gradually expand over time at the radial direction, just like the expansion of the universe. However, unlike MOND, the model in this paper cannot rule out the existence of dark matter. Instead, the mass of dark matter can be used to help to adjust the value of A0(here it just to distinguish from a0 in MOND, and A0and a0have the same meaning in the equation), thereby helping to better fit the radial acceleration relation (RAR) curve of galaxies. However, unlike ΛCDM, even if dark matter exists, it does not need to be carefully adjusted to meet the asymptotically flat rotational velocity curve of galaxies. The rotational curve of galaxies with this characteristic can be also achievedunder the viscous dynamics of the galaxy itself.
分类： 天文学 >> 天体物理学 分类： 天文学 >> 天文学史 提交时间： 2024-10-17
摘要： In recent astronomical discussions, attempts have been made to link the knowndwarf nova Z Cam to historical celestial events, particularly the “guest star” phenomenonreported in China in 77 BCE. Despite other suggestions and the problems with regard to thelocation of the event in 77 BCE, its identification with Z Cam is used in the Variable StarIndeX (VSX) of the AAVSO and in several research papers that aim to derive knowledge onthe evolution of cataclysmic variables. Through the reconstruction of the super-constellationof the Purple Palace in the Han Dynasty, we found that Z Cam is actually located outsidethis enclosure, contradicting the records of the 77 BCE guest star being “within the PurplePalace”. With newly found text versions of the guest star in 77 BCE, we narrowed downthe position given therein. Combined with a new analysis of accompanying divination textleads to the conclusion that this guest star was actually a comet. Finally, through meticulousexamination and comparison, we conclude that the guest star of 369 CE appears the mostplausible candidate for Z Cam’s historical counterpart, aligning with both textual evidenceand modern astronomical observations.
分类： 天文学 >> 天体物理学 提交时间： 2024-10-09
摘要： In creasing observation of microstructures, in particular giantpulses require a pulsar emission mechanism withsmall size, high energy density,pair production along with Alfven wave, which give rise coherent trains responsible for subsequent pulsar emission.However, it is still difficult to reproduce these fundamental elements in polar-cap based models.This paper proposes a reconnection process at the tip of last closed field line region with a current sheet of width, $\sim 10^{-1}$m and length, $10^1$m, in the vicinity of light cylinder.The resultant interaction of triple beams out of the X-line of reconnection site lead tomicostructures distributing in acone-core pattern of pulsar emission.The new scenario can interpret not only the frequency and power of giantpulses, but also theircorrelation with X-ray and PeV emission exhibited in the Crab pulsar.
分类： 天文学 >> 天体物理学 提交时间： 2024-05-20
M. Kharinov
A. Erkenov
T. Semenova
L. Volvach
S. Guo
T. An
Y. Liu
Y. Sotnikova
A. Volvach
T. Mufakharov
L. Chen
L. Cui
A. Wang
Z. Xu
Y. Zhang
W. Xu
Y. A. Kovalev
Y. Y. Kovalev
摘要： Context : Understanding the mechanisms that launch and shape powerful relativistic jets from supermassive black holes (SMBHs) in high-redshift active galactic nuclei (AGN) is crucial for probing the co-evolution of SMBHs and galaxies over cosmic time. Aims :We study the high-redshift ($z=3.396$) blazar OH~471 to explore the jet launching mechanism in the early Universe. Methods : Using multi-frequency radio monitoring observations and high-resolution Very Long Baseline Interferometry imaging over three decades, we study the milliarcsecond structure and long-term variability of OH~471. Results : Spectral modelling of the radio flux densities reveals a synchrotron self-absorbed spectrum indicating strong magnetic fields within the compact core. By applying the flux freezing approximation, we estimate the magnetic flux carried by the jet and find that it reaches or exceeds theoretical predictions for jets powered by black hole spin energy via the Blandford-Znajek mechanism. This implies that OH~471 was in a magnetically arrested disk (MAD) state where the magnetic flux accumulated near the horizon regulates the accretion flow, allowing efficient extraction of black hole rotational energy. Conclusions : Our study demonstrates the dominance of MAD accretion in powering the prominent radio flares and relativistic jets observed in the radio-loud AGN OH~471 and statistical studies of large samples of high-redshift AGN will shed light on the role of MAD accretion in launching and accelerating the earliest relativistic jets.
分类： 天文学 >> 天体物理学 提交时间： 2024-01-22
摘要： 射电天文图像去卷积是射电天文学中的一项关键数据处理技术, 其主要目标是去除天空图像中由天文观测仪器引入的效应, 从而复原原始的天空图像. 射电望远镜阵列采用稀疏干涉阵列, 成像原理与光学望远镜有所不同. 如果UV 空间中的采样点不足够密集, 将会导致在图像重建时无法获得足够高分辨率的信息, 传统的射电天文图像重建算法未能根本解决UV 空间欠采样的问题. 本文基于压缩感知理论框架, 并结合射电天文图像稀疏性的先验知识, 研究了一种新的射电天文图像去卷积算法, 该算法将脏图的去卷积过程转化为一个旨在求解全局最小化的凸优化问题, 即基于IUWT-CS 的射电干涉图像重建算法. 为了评估该算法的重建性能, 研究使用了射电天文学仿真软件包OSKAR 对SKA1-low 射电望远镜阵列进行模拟观测, 并对观测得到的点源和扩展射电源进行了去卷积处理. 实验结果表明, 与HOGBOM-CLEAN、MS-CLEAN和IUWT-FISTA 方法相比, IUWT-CS 方法显著提高了射电图像的重建质量, 实现了更加精细的去噪和复原效果.
分类： 天文学 >> 天体物理学 提交时间： 2024-01-16
摘要： The pulsar radio emission mechanism remains an enigma since over half a century. A radiation process requires not only to explain the coherency and high degree of polarization of the emission, but also nanobursts, characteristic frequency of emission, and problems like death line, which can#2;not be well understood in the context of long standing cap models and recent models of magnetic reconnection. This article proposes a dynamo process in pulsar magnetosphere. Through centrifu#2;gal force the last closed magnetic field lines can be amplified to a critical value of, BT 104T, which triggers magnetic reconnection responsible for the instability required in coherent curvature radiation, so that a number of problems can be interpreted. The time scale of magnetic field pile up and relaxation can be short or long for young or old pulsars respectively, which naturally account for the diverse intermittencies exhibited in pulsars and FRBs.
分类： 天文学 >> 天体物理学 提交时间： 2023-12-29
Zhiyuan Ren
Xi Chen
Tie Liu
Emma Mannfors
Leonardo Bronfman
Fengwei Xu
Siyi Feng
Hongli Liu
Fanyi Meng
Amelia M. Stutz,
Shanghuo Li
Chang Won Lee,
Ke Wang
Jianwen Zhou
Di Li
Chen Wang
Chakali Eswaraiah
Anandmayee Tej
Long-Fei Chen
Hui Shi
摘要： We studied the unique kinematic properties in massive filament G352.63-1.07 at 1000-AU spatial scale with the dense molecular tracers observed with the Atacama Large Millimeter/submillimeter Array (ALMA). We find the central massive core M1 (12 Msun) being separated from the surrounding filament with a velocity difference of v-v_sys=-2 km/s and a transverse separation within 3 arcsec. Meanwhile, as shown in multiple dense-gas tracers, M1 has a spatial extension closely aligned with the main filament and is connected to the filament towards its both ends. M1 thus represents a very beginning state for a massive young star-forming core escaping from the parental filament, within a time scale of ~4000 years. Based on its kinetic energy (3.5x10^44 erg), the core escape is unlikely solely due to the original filament motion or magnetic field, but requires more energetic events such as a rapid intense anisotropic collapse. The released energy also seems to noticeably increase the environmental turbulence. This may help the filament to become stabilized again.
分类： 物理学 >> 核物理学 分类： 天文学 >> 天体物理学 提交时间： 2023-12-28
摘要： 相对论 Brueckner-Hartree-Fock (RBHF) 理论是相对论框架下重要的第一性原理方法，仅包含两体力即可以满意描述核物质的饱和性质。在完备的 Dirac 空间中自洽求解核物质 RBHF 方程，唯一确定了单粒子势的标量和矢量分量，避免了已有工作中由于忽略负能态所导致的不确定性，解决了 40 多年来 RBHF 计算中不能唯一确定单粒子势的问题。文章简要回顾 RBHF 理论的发展历史，阐述包含负能态做 RBHF 计算的必要性，介绍利用完备 Dirac 空间的 RBHF 理论，研究核物质性质和中子星物质性质的最新进展，包括有效质量、纯中子物质的每核子结合能、对称和纯中子物质的压强、中子星物质的粒子分数和状态方程、中子星的质量半径关系和潮汐形变等。文章还展望了完备 Dirac 空间的RBHF 理论在确定密度泛函理论参数、描述核子原子核弹性散射和研究中子星内部强子夸克相变等方面的可能应用。
分类： 天文学 >> 天体物理学 提交时间： 2023-12-17
Yuxiao Wu
Zhichen Pan
Lei Qian
Scott Ransom
BoJun Wang
Zhen Yan
Jintao Luo
Liyun Zhang
Minghui Li
Dejiang Yin
Baoda Li
Yifeng Li
Yinfeng Dai
Yaowei Li
Xinnan Zhang
Tong Liu
Yu Pan
摘要： We present the discovery of three pulsars in Globular Cluster M15 (NGC 7078) by the Five-hundred-meter Aperture Spherical radio Telescope (FAST).In the three pulsars, PSR~J2129+1210J (M15J) is a millisecond pulsar with a spinning period of 11.84 ms and a dispersion measure of 66.68 pc cm$^{-3}$.Both PSR~J2129+1210K and L (M15K and L) are long period pulsars with spinning periods of 1928 ms and 3961 ms, respectively,while M15L is the GC pulsar with the longest spinning period till now.The discoveries of M15K and L support the theory that core-collapsed Globular Clusters may contain partially recycled long period pulsars citep{verbunt-2014-slowpulsar}.With the same dataset, the timing solutions of M15A to H were updated,and the timing parameter P1 of M15F is different from the previous results, which is approximately 0.027$ times 10^{-18} ss^{-1}$ from our work and $0.032 times 10^{-18} ss^{-1}$ from Anderson's citep{anderson-1993}.As predicted by Rodolfi et al. citep{ridolfi-2017},the luminosity of M15C kept decreasing and the latest detection in our dataset is on December 20$^{ rm th}$, 2022.We also detected M15I for one more time.The different barycentric spin periods indicate that this pulsar should locate in a binary system,manifesting itself as the exceptional one in such a core-collapsing GC.
分类： 天文学 >> 天体物理学 提交时间： 2023-12-04
摘要： The pulsar radio emission mechanism remains an enigma over half a century.A successful radiation process requires not only to explain the coherency and high degree of polarization of the emission, but alsomicrostructures, characteristic frequency of emission, and the death line problem, etc. These issues challenge both the long standing cap models and recent models of magnetic reconnection assuming stationary magnetosphere of a pulsar.This article proposes a radio emission through global-local interaction of pulsar magnetosphere. The centrifugal force at the light cylinder leads to the concentration of both field lines and plasma in an equatorial layer much less than that of a pulsar magnetosphere.The resultant magnetic reconnection with chain of plasmoids interprets not only the above problems in a simple and unified way, but also Rotating Radio Transients (RRATs) and Fast Radio Bursts (FRBs).
分类： 天文学 >> 天体物理学 提交时间： 2023-09-15
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分类： 天文学 >> 天体物理学 分类： 天文学 >> 天文学 提交时间： 2023-08-31
摘要： The radiation mechanism of fast radio bursts (FRBs) has been extensively studied but still remains elusive. Coherent radiation is identified as a crucial component in the FRB mechanism, with charged bunches also playing a significant role under specific circumstances. In the present research, we propose a phenomenological model that draws upon the coherent curvature radiation framework and the magnetized neutron star, taking into account the kinetic energy losses of outflow particles due to inverse Compton scattering (ICS) induced by soft photons within the magnetosphere. By integrating the ICS deceleration mechanism for particles, we hypothesize a potential compression effect on the particle number density within a magnetic tube/family, which could facilitate achieving the necessary size for coherent radiation in the radial direction. This mechanism might potentially enable the dynamic formation of bunches capable of emitting coherent curvature radiation along the curved magnetic field. Moreover, we examine the formation of bunches from an energy perspective. Our discussion suggests that within the given parameter space the formation of bunches is feasible. Finally, we apply this model to FRB 20190520B, one of the most active repeating FRBs discovered and monitored by FAST. Several observed phenomena are explained, including basic characteristics, frequency downward drifting, and bright spots within certain dynamic spectral ranges.
分类： 天文学 >> 天体物理学 提交时间： 2023-07-29
摘要： The pulsar radio emission mechanism remains an enigma since its discovery in 1967. The critical issue of origin of coherent emission is usually investigated separately from the micro-structure of individual pulses and characteristic emission frequency of pulsars... In this letter, these issues are interpreted in an unified scenario. The pulsar spin piles up magnetic field at the apex of last closed field line triggering magnetic reconnection. The resultant Alfven wave interacts with open field lines giving rise to coherent maser curvature and cyclotron emission. Such a scenario of coherent emission not only imposes new limit to emission site, nanoburst, and characteristic frequency, but also affects polarization and pair production required in maintaining a marginal stable circuit in radio emission of pulsars.
分类： 天文学 >> 天体物理学 提交时间： 2023-07-23
摘要： The distance $D$ to an exoplanet system with imaging and spectral measurement can be obtained by using the orbit as a ruler. The measurement of the Distance to a typical exoplanet system with imaging and spectral measurement can be accurate to $\delta D/D\sim 0.2$, if the orbital velocity of the planet can be accurate to $\sim 3 {\ \rm km/s}$.
分类： 天文学 >> 天体物理学 提交时间： 2023-07-11
摘要： We propose to use the rotation period to constrain the average density of an object with gravitationally confined surface. The average density is inverse proportional to the square of the rotation period, while independent of the size of the object. The lower limit of the average density can be written as $\rho_0=10.9 {\ \rm g\ cm^{-3}}\left(\frac{{\ \rm hours}}{P}\right)^2$. An asteroid with rotating period shorter than 0.7 h should consist of some unknown matter, or it is a whole rock or a bulk of ice with no rubble piles on the surface.
分类： 天文学 >> 天体物理学 分类： 物理学 >> 地球物理学、天文学和天体物理学 提交时间： 2023-05-30
摘要： According to the CDM cosmological model, dark matter has a very long history and remains a puzzle. X-ray observations suggest that the best candidate of dark matter is cosmic plasma. It is only because in the CDM cosmological model, the mass of the cosmic plasma is limited to less than 5% of the critical mass of the universe (i.e. b order to guarantee the conjecture that the observed CMB is a remnant of the Big Bang with a perfect blackbody spectrum, that this X-ray observational evidence is unreasonably ignored. If astrophysicists could discard the unreasonable assumption: i.e. b matter puzzle would be easy to solve. Dark matter is actually cosmic plasma
分类： 天文学 >> 天体物理学 提交时间： 2023-05-16
摘要： 日冕是太阳大气活动的关键区域, 是日地空间天气的源头. 受观测限制, 人们对日冕低层大气等离子体结构和磁场状态的研究非常欠缺, 国际上对于可见光波段日冕低层大气的亮度分层研究很少. 本文利用丽江日冕仪YOGIS(Yunnan Green-line Imaging System) 的日冕绿线（FeXIV 5303 ）观测资料, 对内日冕区域（1.03R⊙-1.25R⊙）亮结构及其中冕环进行了有效的强度衰减分析. 本文通过对亮结构的强度在太阳径向高度上进行了指数衰减拟合, 比较这些拟合结果发现所得到的静态内冕环的衰减指数在一固定值附近. 然后将比较明显的冕环提取出来, 通过对不同高度的强度进行相同的指数拟合, 得出的衰减指数与亮结构中也比较相近, 这对进一步研究日冕中的各项物理参数演化提供了参考.
分类： 天文学 >> 天体物理学 提交时间： 2023-02-21
Chaojun Wang
B. Luo
W. N. Brandt
D. M. Alexander
F. E. Bauer
S. C. Gallagher
Jian Huang
Hezhen Liu
D. Stern
摘要： We utilize recent NuSTAR observations (co-added depth 55-120 ks) of PG 1001+054, PG 1254+047, and PHL 1811 to constrain their hard X-ray (≳5 keV) weakness and spectral shapes, and thus to investigate the nature of their extreme X-ray weakness. These quasars showed very weak soft X-ray emission, and they were proposed to be intrinsically X-ray weak, with the X-ray coronae producing weak continuum emission relative to their optical/UV emission. However, the new observations suggest an alternative explanation. The NuSTAR 3-24 keV spectral shapes for PG 1001+054 and PHL 1811 are likely flat (effective power-law photon indices \Gamma_{\rm eff}=1.0^{+0.5}_{-0.6} and \Gamma_{\rm eff}=1.4^{+0.8}_{-0.7}, respectively), while the shape is nominal for PG 1254+047 (\Gamma_{\rm eff}=1.8\pm0.3). PG 1001+054 and PHL 1811 are significantly weak at hard X-ray energies (by factors of 26-74 at rest-frame 8 keV) compared to the expectations from their optical/UV emission, while PG 1254+047 is only hard X-ray weak by a factor of 3. We suggest that X-ray obscuration is present in all three quasars. We propose that, as an alternative to the intrinsic X-ray weakness + X-ray obscuration scenario, the soft and hard X-ray weakness of these quasars can be uniformly explained under an obscuration-only scenario. This model provides adequate descriptions of the multi-epoch soft and hard X-ray data of these quasars, with variable column density and leaked fraction of the partial-covering absorber. We suggest that the absorber is the clumpy dust-free wind launched from the accretion disk. These quasars probably have super-Eddington accretion rates that drive powerful and high-density winds.
分类： 天文学 >> 天体物理学 提交时间： 2023-02-21
Weicheng Zang
Youn Kil Jung
Hongjing Yang
Xiangyu Zhang
Andrzej Udalski
Jennifer C. Yee
Andrew Gould
Shude Mao
摘要： We present the analysis of seven microlensing planetary events with planet/host mass ratios q < 10^{-4}: KMT-2017-BLG-1194, KMT-2017-BLG-0428, KMT-2019-BLG-1806, KMT-2017-BLG-1003, KMT-2019-BLG-1367, OGLE-2017-BLG-1806, and KMT-2016-BLG-1105. They were identified by applying the Korea Microlensing Telescope Network (KMTNet) AnomalyFinder algorithm to 2016--2019 KMTNet events. A Bayesian analysis indicates that all the lens systems consist of a cold super-Earth orbiting an M or K dwarf. Together with 17 previously published and three that will be published elsewhere, AnomalyFinder has found a total of 27 planets that have solutions with q < 10^{-4} from 2016--2019 KMTNet events, which lays the foundation for the first statistical analysis of the planetary mass-ratio function based on KMTNet data. By reviewing the 27 planets, we find that the missing planetary caustics problem in the KMTNet planetary sample has been solved by AnomalyFinder. We also find a desert of high-magnification planetary signals (A≳65), and a follow-up project for KMTNet high-magnification events could detect at least two more q < 10^{-4} planets per year and form an independent statistical sample.
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