分类： 天文学 >> 星系和宇宙学 提交时间： 2025-02-21
摘要： The paper Baruch (2025a) shows that there is an apparent wavelength-independent extinction coefficient of 0.06 magnitudes per kiloparsec across the Milky Way. Baruch 2025b) shows that the Hubble constant values of Riess et al (2016, 2018a and 2018b), Freedman et al (2019) and the Planck satellite (Ade et al 2014) coincide if the extinction coefficient is a function of the density of dark matter. This wavelength-independent extinction has a frequency threshold between 160Ghz and 300 Thz. This paper seeks a possible process by which dark matter can absorb light.The current data on dark matter is reviewed to determine how dark matter could act as a wavelength-independent absorber of light in the visible frequencies. The discussion of the role of inertia and momentum in general relativity and its relationship with the other forces since the Einstein paper on General Relativity of 1915 is reviewed. It is conjectured that for a pair of gravitationally bound dark matter particles a photon with sufficient momentum would effectively “ionise” the pair, releasing the two dark matter particles, and absorbing the photon. The approximate mass of the dark matter particle is derived. It is suggested that this dark matter extinction provides real data to help settle the role of inertia and momentum in General Relativity. A test for the “ionisation” process is suggested.
分类： 物理学 >> 地球物理学、天文学和天体物理学 分类： 数学 >> 数学物理 提交时间： 2024-12-10
摘要： Photon sphere has attracted considerable interests in the studies of black hole and other astrophysical objects. For different categories of spacetimes (or gravitational sources), the existence of photon spheres and their distributions are dramatically influenced by geometric and topological properties of spacetimes and characteristics of the corresponding gravitational fields. In this work, we carry out a geometric analysis on photon spheres for different categories of spacetime (including black hole spacetime, ultra-compact object’s spacetime, regular spacetime, naked singularity spacetime). Some universal properties and conclusions are obtained for these spacetimes. We mostly focus on the existence of photon spheres, total number of photon spheres $n = n_{\text{stable}} + n_{\text{unstable}}$, the subtraction of stable photon sphere and unstable photon sphere $w = n_{\text{stable}} - n_{\text{unstable}}$ in different categories of spacetimes. These conclusions are derived solely from geometric properties of optical geometry of spacetimes, irrelevant to the specific spacetime metric forms. Besides, our results successfully recover some important theorems on photon spheres proposed in recent years.
分类： 天文学 >> 天体物理学 提交时间： 2023-02-21
H. Hu
M. Kramer
D. J. Champion
N. Wex
A. Parthasarathy
T. T. Pennucci
N. K. Porayko
W. van Straten
V. Venkatraman Krishnan
M. Burgay
P. C. C. Freire
R. N. Manchester
A. Possenti
I. H. Stairs
M. Bailes
S. Buchner
A. D. Cameron
F. Camilo
M. Serylak
摘要： The Double Pulsar, PSR J0737-3039A/B, has offered a wealth of gravitational experiments in the strong-field regime, all of which GR has passed with flying colours. In particular, among current gravity experiments that test photon propagation, the Double Pulsar probes the strongest spacetime curvature. Observations with MeerKAT and, in future, the SKA can greatly improve the accuracy of current tests and facilitate tests of NLO contributions in both orbital motion and signal propagation. We present our timing analysis of new observations of PSR J0737-3039A, made using the MeerKAT telescope over the last 3 years. The increased timing precision offered by MeerKAT yields a 2 times better measurement of Shapiro delay parameter s and improved mass measurements compared to previous studies. In addition, our results provide an independent confirmation of the NLO signal propagation effects and already surpass the previous measurement from 16-yr data by a factor of 1.65. These effects include the retardation effect due to the movement of B and the deflection of the signal by the gravitational field of B. We also investigate novel effects which are expected. For instance, we search for potential profile variations near superior conjunctions caused by shifts of the line-of-sight due to latitudinal signal deflection and find insignificant evidence with our current data. With simulations, we find that the latitudinal deflection delay is unlikely to be measured with timing because of its correlation with Shapiro delay. Furthermore, although it is currently not possible to detect the expected lensing correction to the Shapiro delay, our simulations suggest that this effect may be measured with the full SKA. Finally, we provide an improved analytical description for the signal propagation in the Double Pulsar system that meets the timing precision expected from future instruments such as the full SKA.
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