中国脉冲星计时阵

2016年,激光干涉引力波天文台(LIGO)宣布探测到两个恒星级质量黑洞合并产生的百赫兹引力波,由此打开了引力波天文学时代的序幕。在经过数十年的努力之后,2023年6月,包括中国在内的国际上多个脉冲星计时阵合作组也宣布对宇宙的低频交响——纳赫兹引力波的搜寻取得重要进展。文章将介绍这几个合作组之一——中国脉冲星计时阵合作组的发展历程、观测与数据情况,以及其在纳赫兹引力波探测的进展,最后讨论对未来的展望。     

用零输出的设备探测引力波

理论估计传到地球上的引力波非常弱,激光干涉引力波探测器被设计用来探测引力波,在没有引力波传来时,激光干涉引力波探测器应该是零输出。为达到这样的目的,必须和众多的噪声作斗争。     

ESSAY: The Cosmological Constant Problem in Brane-Worlds and Gravitational Lorentz Violations

Brane worlds are theories with extra spatial dimensions in which ordinary matter is localized on a (3+1) dimensional submanifold. Such theories could have interesting consequences for particle physics and gravitational physics. In this essay we concentrate on the cosmological constant (CC) problem in the context of brane worlds. We show how extra-dimensional scenarios may violate Lorentz invariance in the gravity sector of the effective 4D theory, while particle physics remains unaffected. In such theories the usual no-go theorems for adjustment of the CC do not apply, and we indicate a possible explanation of the smallness of the CC. Lorentz violating effects would manifest themselves in gravitational waves travelling with a speed different from light, which can be searched for in gravitational wave experiments.     

Gaussian Beams of Gravitational Wave

The standard and high-order Gaussian beam solutions for gravitational wave is obtained in the linear approximation of vacuum Einstein equation under harmonic conditions.     

Cosmology with Curvature-Saturated Gravitational Lagrangian R/\sqrt {1 + l^4 R^2 }

We argue that the Lagrangian for gravity should remain bounded at large curvature, and interpolate between the weak-field tested Einstein-Hilbert Lagrangian _EH = R/16G and a pure cosmological constant for large R with the ansatz _cs = _EH/ , where l is a length parameter expected to be a few orders of magnitude above the Planck length. The curvature-dependent effective gravitational constant defined by d/dR = 1/16G _eff is G _eff = G , and tends to infinity for large R, in contrast to most other approaches where G _eff 0. The theory possesses neither ghosts nor tachyons, but it fails to be linearization stable. In a curvature saturated cosmology, the coordinates with ds ² = a ² [da ²/B(a) – dx ² – dy ² – dz ²] are most convenient since the curvature scalar becomes a linear function of B(a). Cosmological solutions with a singularity of type R ± are possible which have a bounded energy-momentum tensor everywhere; such a behaviour is excluded in Einstein's theory. In synchronized time, the metric is given by

Gravitational Wave Holography

We represent and discuss a theory of gravitational holography in which all the involved waves; subject, reference and illuminator are gravitational waves (GW). Although these waves are so weak that no terrestrial experimental set-ups, even the large LIGO, VIRGO, GEO and TAMA facilities, were able up to now to directly detect them they are, nevertheless, known under certain conditions (such as very small wavelengths) to be almost indistinguishable (see P. 962, in Misner, C. W., Thorne, K. S., and Wheeler, J. A. (1973). Gravitation, Freeman, San Francisco.) from their analogue electromagnetic waves (EMW). We, therefore theoretically, show, using the known methods of optical holography and taking into account the very peculiar nature of GW, that it is also possible to reconstruct subject gravitational waves. PACS numbers: 42.40.-i, 42.40.Eq, 04.30.-w, 04.30.Nk     

Noise Characterization for Laser Interferometer Gravitational Wave Detectors

This work incorporates a review of the status, in Australia, of data analysis for gravitational wave detection using laser interferometers, within an overview of the present state of such research in the world generally. In this context, data analysis refers not so much to signal simulation as to what might be called the thorough process of noise characterization and the subsequent, quality-controlled signal extraction. To the extent that problems identified here arise for all currently planned instruments, there is necessarily a global component to the discussion presented. In Australia, there are unique circumstances, associated with attempting to carry out work in gravitational wave detection, which demand also a local aspect to the ensuing discussion.     

欧洲脉冲星计时阵

脉冲星计时阵是星系尺度的引力波探测器,通过对多个毫秒脉冲星进行长期计时观测来探测低频纳赫兹引力波,可能的引力波源有星系中心超大质量双黑洞的并合和早期宇宙的物理过程等。2023年,国际上多个脉冲星计时阵团队宣布发现了纳赫兹引力波存在的证据。在利用脉冲星计时阵探测低频引力波的研究中,欧洲具有长久的历史和重要的贡献。文章介绍欧洲脉冲星计时阵的发展历程、观测数据、早期科学研究和最新进展。     

帕克斯脉冲星计时阵

2023年,国际上几个脉冲星计时阵团队同时独立宣布发现了纳赫兹引力波背景信号的证据。这预示着一扇全新的引力波天文学观测窗口即将打开。帕克斯脉冲星计时阵是第一个正式运行的脉冲星计时阵实验,在研发先进的脉冲星观测仪器和高效的数据处理软件、发展脉冲星计时噪声分析和引力波搜寻方法等方面做出了开创引领性贡献。文章将介绍帕克斯脉冲星计时阵的发展历程、对领域的独特贡献和最新的研究成果。     

空间引力波探测计划-LISA系统设计要点

为了验证广义相对论,世界各国竞相开展了空间引力波探测方面的研究。本文以欧洲空间引力波探测LISA(Laser Interferometer Space Antenna)计划为例,根据基线设计,对LISA系统有效载荷及主要组件的设计进行了分析和阐述。LISA主要探测和研究低频引力波辐射,其工作频段为10^-3~1 Hz,工作距离为5×10⁶ km,预计能探测到双致密星系统以及星系合并引起的超大质量并合等波源,测距精度达到pm量级。以上研究希望能对我国未来的空间引力波探测计划有一定启示。     

2017年诺贝尔物理学奖解读

文章简单解读了2017年诺贝尔物理学奖,获奖者的主要贡献,目前观测到的几个引力波事件,美国LIGO项目的简单历史,以及引力波观测对基础物理、宇宙学和天体物理的科学意义。     

千新星简介

中子星—中子星或中子星—黑洞组成的致密双星系统在发生并合时,潮汐离心、碰撞挤压和吸积反馈等作用会导致约千分之几到百分之几倍太阳质量的物质被抛射到星际空间中。这些抛射物在加热机制的作用下可能达到较高的温度并快速膨胀,从而在紫外光学近红外波段发出一种快速变化的热辐射,即为千新星辐射。决定于抛射物的质量和不透明度,千新星的特征光变时标可估计在天到星期的量级。其辐射光度至少可达10&;amp;lt;sup&;amp;lt;41&;amp;lt;/sup&;amp;lt; erg s&;amp;lt;sup&;amp;lt;-1&;amp;lt;/sup&;amp;lt;的量级,具体决定于热源的性质,包括抛射物中通过快中子俘获过程形成的重元素的放射性衰变和并合产物可能的持续能量释放。千新星现象在2017年8月的GW170817引力波事件中被首次观测证实。     

Binary compact object inspiral: Detection expectations

We review the current estimates of binary compact object inspiral rates in particular in view of the recently discovered highly relativistic binary pulsar J0737-3039. One of the robust results is that, because of this discovery, the rate estimates for binary neutron stars have increased by a factor of 6–7 independent of any uncertainties related to the pulsar population properties. This rate increase has dramatic implications for gravitational wave detectors. For initial LIGO, the most probable detection rates for double neutron star (DNS) inspirals is 1 event/(5-250) yr; at 95% confidence we obtain rates up to 1/1.5 yr. For advanced LIGO, the most probable rates are 20–1000 events/yr. These predictions, for the first time, bring the expectations for DNS detections by initial LIGO to the astrophysically relevant regime. We also use our models to predict that the largescale Parkes multibeam pulsar survey with acceleration searches could detect an average of three to four binary pulsars similar to those known at present. In comparison, rate estimates for binaries with black holes are derived based on binary evolution calculation, and based on the optimistic ends of the ranges, remain an important candidate for inspiral detection in the next few years. We also consider another aspect of the detectability of binary inspiral: the effect of precession on the detection efficiency of astrophysically relevant binaries. Based on our current astrophysical expectations, large tilt angles are not favored. As a result the decrease in detection rate varies rather slowly with black hole spin magnitude and is within 20–30% of the maximum possible values.