The Event Horizon Telescope has mapped the central compact radio source of the elliptical galaxy M87 at 1.3 mm with unprecedented angular resolution. These images show a prominent ring with a diameter of ~40 micro-arcsecond, consistent with the size and shape of the lensed photon orbit encircling the “shadow” of a supermassive black hole. Recently EHT has provided new images of the polarised...
Gamma-ray bursts (GRBs) might be powered by black hole (BH) hyperaccretion systems via the Blandford–Znajek (BZ) mechanism or neutrino annihilation from neutrino-dominated accretion flows (NDAFs). Magnetic coupling (MC) between the inner disc and BH can transfer angular momentum and energy from the fast-rotating BH to the disc. The neutrino luminosity and neutrino annihilation luminosity are...
The theory of General Relativity has successfully passed a large number of observational tests. The theory has been extensively tested in the weak-field regime with experiments in the Solar System and observations of binary pulsars. The past five years have seen significant advancements in the study of the strong-field regime, which can now be tested with gravitational waves, X-ray data, and...
We discuss the possibility that accreting black hole systems could be sources for dark matter flux through several different mechanisms. We firstly discuss two types of systems: coronal thermal plasmas around supermassive black holes in active galactic nuclei (AGNs), and accretion disks of stellar-mass X-ray black hole binaries (BHBs). We explore how these black hole systems may produce keV...
In this talk, I will revisit the condition for the thermal equilibrium of charged fluids in electromagnetic fields and gravitational fields, where the Tolman like law is derived by the maximal entropy principle from scratch. As a warm up, I will first address the case with the electromagnetic fields and gravitational fields fixed as background fields. After this, I will move onto the charged...
Ultralight bosons can be abundantly produced through superradiance process by a spinning black hole and form a bound state with hydrogen-like spectrum. We show that such a "gravitational atom" typically possesses anomalously large mass quadrupole and leads to significant orbital precession when it forms an eccentric binary with a second compact object. Dynamically formed black hole binaries or...
A dense and luminous star cluster exists in the central parsecs of the Milky Way. S2 is one of the most interesting targets whose pericenter is about ~5x10^-3 pc from the supermassive black hole. Recently both the GRAVITY and Keck groups have published their observations on the S2 star around its closest approach, which provides us a good chance to probe the properties of dark matter (DM)...
In this work, we study the relation of the eikonal quasinormal modes (EQNMs) and the unstable fundamental photon orbits (UFPOs) in the Kerr-Newman spacetime. We find that in the eikonal limit the gravitational and electromagnetic perturbations of the KerrNewman black hole are naturally decoupled, and a single one-dimensional Schr¨odinger-like equation encoding the QNM spectrum can be derived....
The fast developments of radio astronomy open a new window to explore the properties of dark matter. In this talk, I will introduce our recent work on this topic, constraining WIMP annihilation from the Event Horizon Telescope obsevations of the M87 supermassive black hole. Assuming the existence of a spiky dark matter density profile, we derive the new limits on the WIMP annihilation cross...
