The Precursor of GRB211211A:A Tide-induced Giant Quake?

The equilibrium configuration of a solid strange star in the final inspiral phase with another compact object is generally discussed,and the starquake-related issue is revisited,for a special purpose to understand the precursor emission of binary compact star merger events(e.g.,that of GRB211211A).As the binary system inspirals inward due to gravitational wave radiation,the ellipticity of the solid strangeon star increases due to the growing tidal field of its compact companion.Elastic energy is hence accumulated during the inspiral stage which might trigger a starquake before the merger when the energy exceeds a critical value.The energy released during such starquakes is calculated and compared to the precursor observation of GRB211211 A.The result shows that the energy might be insufficient for binary strangeon-star case unless the entire solid strangeon star shatters,and hence favors a black hole-strangeon star scenario for GRB211211A.The timescale of the precursor as well as the frequency of the observed quasi-periodic-oscillation have also been discussed in the starquake model.

Scientific objectives of the Hot Universe Baryon Surveyor(HUBS) mission

The Hot Universe Baryon Surveyor(HUBS) is a proposed space-based X-ray telescope for detecting X-ray emissions from the hot gas content in our universe. With its unprecedented spatially-resolved high-resolution spectroscopy and large field of view,the HUBS mission will be uniquely qualified to measure the physical and chemical properties of the hot gas in the interstellar medium, the circumgalactic medium, the intergalactic medium, and the intracluster medium. These measurements will be valuable for two key scientific goals of HUBS, namely to unravel the AGN and stellar feedback physics that governs the formation and evolution of galaxies, and to probe the baryon budget and multi-phase states from galactic to cosmological scales. In addition to these two goals, the HUBS mission will also help us solve some problems in the fields of galaxy clusters, AGNs, difuse X-ray backgrounds, supernova remnants, and compact objects. This paper discusses the perspective of advancing these fields using the HUBS telescope.

Perceiving deci-Hertz gravitational waves over the Moon

The field of experimental gravitational waves(GWs)started in 1960s with Joseph Weber and his resonant bars which monitor GW-excited vibration of elastic bodies.In 2015,laser-interferometric detectors,as Weber bars’descendant,made the first detection of GWs in the kilo-Hertz band,and opened up a completely new window to observe the gravitational Universe[1].GWs from coalescing black holes and neutron stars are cataloged.

Observatory science with eXTP

In this White Paper we present the potential of the enhanced X-ray Timing and Polarimetry(eXTP) mission for studies related to Observatory Science targets. These include flaring stars, supernova remnants, accreting white dwarfs, low and high mass X-ray binaries, radio quiet and radio loud active galactic nuclei, tidal disruption events, and gamma-ray bursts. eXTP will be excellently suited to study one common aspect of these objects: their often transient nature. Developed by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Science, the eXTP mission is expected to be launched in the mid 2020s.

Tests of gravitational symmetries with radio pulsars

Symmetries play important roles in modern theories of physical laws. In this paper, we review several experimental tests of important symmetries associated with the gravitational interaction, including the universality of free fall for self-gravitating bodies,time-shift symmetry in the gravitational constant, local position invariance and local Lorentz invariance of gravity, and spacetime translational symmetries. Recent experimental explorations for post-Newtonian gravity are discussed, of which, those from pulsar astronomy are highlighted. All of these tests, of very different aspects of gravity theories, at very different length scales, favor to very high precision the predictions of the strong equivalence principle(SEP) and, in particular, general relativity which embodies SEP completely. As the founding principles of gravity, these symmetries are motivated to be promoted to even stricter tests in future.

引力波视角下的世界图景

自古希腊以来,人们一直都在探索茫茫星空的无尽奥秘.1609年的秋天,45岁的意大利天文学家伽利略(Galileo Galilei)把望远镜指向了天空,打开了一扇观测宇宙的窗口,彻底改变了人类对世界的认识.伽利略本人也被后人尊称为"现代科学之父"和"观测天文学之父".如今,人们已经不再局限于通过肉眼和可见光来观测星空.

Accretion in strong field gravity with eXTP

In this paper we describe the potential of the enhanced X-ray Timing and Polarimetry(eXTP) mission for studies related to accretion flows in the strong field gravity regime around both stellar-mass and supermassive black-holes. eXTP has the unique capability of using advanced "spectral-timing-polarimetry" techniques to analyze the rapid variations with three orthogonal diagnostics of the flow and its geometry, yielding unprecedented insight into the inner accreting regions, the effects of strong field gravity on the material within them and the powerful outflows which are driven by the accretion process.

中子星:引力检验的极端实验室

Neutrons were discovered 90 years ago by James Chadwick.The concept of neutron stars was hypothesized around that time by Lev Landau,Walter Baade,and Fritz Zwicky,and it was further developed by Richard Tolman,Robert Oppenheimer,George Volkoff,and other physicists.Neutron stars are astrophysical compact objects formed after the death of massive stars(more massive than our own Sun).According to current understanding,the typical mass of neutron stars is comparable to that of the Sun,while the radius is only~10km.As its name implies,the main interior ingredients of such stars are neutrons,but they also consist of protons,electrons,muons,and presumably even more exotic particles,like hyperons,kaons,or quarks.The field of neutron stars was bolstered by the discovery of radio pulsars by Jocelyn Bell Burnell,Antony Hewish,and collaborators in 1967[1].A famous achievement brought forth by the first binary pulsar,the so-called Hulse-Taylor pulsar,is the first-ever empirical proof that gravitational waves exist in our Universe[2].In 2017,the first binary neutron star merger was observed directly via gravitational waves(ripples of spacetime)and accompanied by enormous electromagnetic follow-up observations[3].

Imaging supermassive black hole shadows with a global very long baseline interferometry array

The imaging of two supermassive black holes by the Event Horizon Telescope Collaboration proved to a new level the correctness of Einstein's general relativity,regarding its prediction of black hole shadows in the highly curved spacetime regime.