New results from testing relativistic gravity with radio pulsars

We experience a golden era in testing and exploring relativistic gravity. Whether it is results from gravitational-wave detectors, satellite or lab experiments, radio astronomy plays an important complementary role. Here, one can mention the cosmic microwave background, black hole imaging and, obviously, binary pulsars. This talk will concentrate on the latter and new results from studies of strongly self-gravitating bodies with unrivalled precision. This presentation compares the results to other methods, discusses implications for other areas of relativistic astrophysics and will give an outlook of what we can expect from new instruments in the near future.

The first results of PandaX-4T

Dark matter, an invisible substance which constitutes 85% of the matter in the observable universe, is one of the greatest puzzles in physics and astronomy today. Dark matter can be made of a new type of fundamental particle, not yet observed due to its feeble interactions with visible matter. In this talk, we present the first results of PandaX-4T, a 4-ton-scale liquid xenon dark matter observatory, searching for these dark matter particles from deep underground. We will briefly summarize the performance of PandaX-4T, introduces details in the data analysis, and present the latest search results on dark matter-nucleon interactions.

Generalized tachyonic dark energy

In this paper, a generalized tachyonic dark energy scenario is presented in the framework of a homogeneous and isotropic Friedmann–Lemaître–Robertson–Walker (FLRW) flat universe, in which a noncanonical scalar field is coupled to gravity nonminimally. By utilizing the Noether symmetry method, we found the explicit form of both potential density and coupling function, as a function of the scalar field. It is found that the tachyon field acts as the source of inflation and accelerates the evolution of the universe in the early times considerably. While, in the late times, gravitational sources are a pressureless matter field together with the tachyon field, which is the nature of dark energy and plays an essential role in the deceleration-acceleration phase transition of the universe. Further, the role of the coefficient function of tachyon potential, alongside the potential, is considered in the evolution of the universe. It is shown that this model involves a cosmological degeneracy in the sense that different coupling parameters and tachyonic potentials may be equivalent to the same cosmological standards such as the cosmic acceleration, age, equation of state and mean Hubble of the FLRW universe. The physical characteristics of the main cosmological observables are studied in detail, which suggests that the generalized tachyon field is a remarkable dark energy candidate.

Traversable wormhole in logarithmic f(R) gravity by various shape and redshift functions

In this paper, we study the traversable wormhole solutions for a logarithmic corrected [Formula: see text] model by considering two different statements of shape [Formula: see text] and redshift [Formula: see text] functions. We calculate the parameters of the model including energy density [Formula: see text], tangential pressure [Formula: see text] and radial pressure [Formula: see text] for the corresponding forms of the functions. Then, we investigate different energy conditions such as null energy condition, weak energy condition, dominant energy condition and strong energy condition for our considered cases. Finally, we explain the satisfactory conditions of energy of the models by related plots.

The irreducible mass of Christodoulou–Ruffini–Hawking mass formula

We reveal three new discoveries in black hole physics previously unexplored in the Hawking era. These results are based on the remarkable 1971 discovery of the irreducible mass of the black hole by Christodoulou and Ruffini, and subsequently confirmed by Hawking. (1) The Horizon Mass Theorem states that the mass at the event horizon of any black hole — neutral, charged, or rotating — is always twice its irreducible mass observed at infinity. (2) The External Energy Theorem asserts that the rotational energy of a Kerr black hole exists completely outside the horizon. This is due to the fact that the irreducible mass does not contain rotational energy. (3) The Moment of Inertia Theorem shows that every black hole has a moment of inertia. When the rotation stops, the irreducible mass of a Kerr black hole becomes the moment of inertia of a Schwarzschild black hole. This is recognized as the rotational equivalent of the rest mass of a moving body in relativity. Thus after 50 years, the irreducible mass has gained a new and profound significance. No longer is it a limiting value in rotation, it determines black hole dynamics and structure. What is believed to be a black hole is a mechanical body with an extended structure. Astrophysical black holes are likely to be massive compact objects from which light cannot escape.

Schrödinger equation in a general curved spacetime geometry

In this paper, we consider relativistic quantum field theory in the presence of an external electric potential in a general curved spacetime geometry. We utilize Fermi coordinates adapted to the time-like geodesic to describe the low-energy physics in the laboratory and calculate the leading correction due to the curvature of the spacetime geometry to the Schrödinger equation. We then compute the nonvanishing probability of excitation for a hydrogen atom that falls in or is scattered by a general Schwarzschild black hole. The photon emitted from the excited state by spontaneous emission extracts energy from the black hole, increases the decay rate of the black hole and adds to the information paradox.

First results of LHAASO

The Large High Altitude Air Shower Observatory (LHAASO) has recently published the first results, including the discovery of 12 ultrahigh-energy gamma-ray sources (with emission above 100[Formula: see text]TeV) above [Formula: see text] confidence level and a detailed analysis of Crab Nebula. This contribution gives a brief introduction to the LHAASO experiment and its recent discoveries.

Effects of the external magnetic field on the Lense–Thirring precession

In this paper, we study the effects of the external magnetic field on the Lense–Thirring (LT) precession of a test gyroscope attached to an observer in magnetized black hole spacetime. For this, we consider a Kerr–Newman black hole embedded in the external magnetic field. The LT precession of a test gyroscope diverges near the ergosurface and remains finite everywhere outside the ergosurface. It is seen that by increasing the external magnetic field, the LT precession frequency in the region of large [Formula: see text] decreases as [Formula: see text] increases, while the precession frequency in the region of small [Formula: see text] increases as [Formula: see text] increases, whereas it increases with increasing the charge of the black hole. The LT precession of a test gyroscope attached to observers moving along the directions close to the polar axis is greater than that of the observer moving in the equatorial plane.

Kinematics of the Milky Way Thick disk in solar neighborhood

Using GAIA EDR3 catalog, we present the detailed analysis of the two-component Milky Way stellar disk in the solar neighborhood. To determine the kinematical properties of the thin and of the Thick disks, we select the complete sample of about 278,000 evolved red giant branch (RGB) stars distributed in the cylinder of 1 kpc radius and 0.5 kpc height centered at the Sun. We measured the following mean velocities and dispersions for the thin and the Thick disks, respectively: [Formula: see text][Formula: see text]km s[Formula: see text] with [Formula: see text][Formula: see text]km s[Formula: see text], and [Formula: see text][Formula: see text]km s[Formula: see text] with [Formula: see text][Formula: see text]km s[Formula: see text]. Errors in mean velocities and dispersions are all less than 1[Formula: see text]km s[Formula: see text]. Same values were computed on much smaller subsamples of our Gaia data with RAVE DR5 [Fe/H] values, from which a metallicity selection was added. Results are basically the same. We find that up to 500 pc height above/below the galactic plane, Thick disk stars comprise about half the stars of the disk. We also find evidence of a substructure in [Formula: see text] versus [Formula: see text] in the thick disk population mostly that would give support to the accretion scenario for the formation of the thick disk.

New dynamical features of pure k-essential cosmologies

We come back on the dynamical properties of [Formula: see text]-essential cosmological models and show how the interesting phenomenological features of those models are related to the existence of boundaries in the phase surface. We focus our attention to the branching curves where the energy density has an extremum and the effective speed of sound diverges. We discuss the behaviour of solutions of a general class of cosmological models exhibiting such curves and give two possible interpretations; the most interesting possibility regards the arrow of time that is reversed in trespassing the branching curve. This study teaches to us something new about general FLRW cosmologies where the fluids driving the cosmic evolution have equations of state that are multivalued functions of the energy density and other thermodynamical quantities.