Dwarf galaxies are characterised by a very low luminosity and low mass. Because of significant accretion and ejection activity of massive black holes, some dwarf galaxies also host low-luminosity active galactic nuclei (AGNs). In a few dwarf AGNs, very long baseline interferometry (VLBI) observations have found faint non-thermal radio emission. SDSS J090613.77+561015.2 is a dwarf AGN owning an intermediate-mass black hole (IMBH) with a mass of |$M_\mathrm{BH} = 3.6^{+5.9}_{-2.3}\times 10^5 M_{\odot }$| and showing a rarely-seen two-component radio structure in its radio nucleus. To further probe their nature, i.e. the IMBH jet activity, we performed additional deep observations with the European VLBI Network (EVN) at 1.66 GHz and 4.99 GHz. We find the more diffuse emission regions and structure details. These new EVN imaging results allow us to reveal a two-sided jet morphology with a size up to about 150 mas (projected length ∼140 pc) and a radio luminosity of about 3 × 10³⁸ erg s⁻¹. The peak feature has an optically thin radio spectrum and thus more likely represents a relatively young ejecta instead of a jet base. The EVN study on SDSS J090613.77+561015.2 demonstrates the existence of episodic, relatively large-scale and powerful IMBH jet activity in dwarf AGNs. Moreover, we collected a small sample of VLBI-detected dwarf AGNs and investigated their connections with normal AGNs. We notice that these radio sources in the dwarf AGNs tend to have steep spectra and small linear sizes, and possibly represent ejecta from scaled-down episodic jet activity.

We have investigated the environment of the giant radio galaxy NGC 315 with its associated group of galaxies selected by their spectroscopic redshift

Theories and simulations predict that intense space-time curvature near black holes bends the trajectories of light and matter, driving disk and jet precession under relativistic torques. However, direct observational evidence of disk-jet coprecession remains elusive. Here, we report the most compelling case to date: a tidal disruption event (TDE) exhibiting unprecedented 19.6-day quasi-periodic variations in both x-rays and radio, with x-ray amplitudes exceeding an order of magnitude. The nearly synchronized x-ray and radio variations suggest a shared mechanism regulating the emission regions. We demonstrate that a disk-jet Lense-Thirring precession model successfully reproduces these variations while requiring a low-spin black hole. This study uncovers previously uncharted short-term radio variability in TDEs, highlights the transformative potential of high-cadence radio monitoring, and offers profound insights into disk-jet physics.

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the largest single-dish radio telescope in the world, and is now being commissioned after the first light in September 2016. Very long baseline interferometry (VLBI) is among the key science topics according to the original design. The FAST VLBI system has been established, and the first VLBI fringe has been successfully obtained. FAST will significantly improve the sensitivity of the existing VLBI networks in the future, and some science projects in need of high sensitivity will benefit from its participation.

Galaxies of stars are building blocks of the baryonic universe. Their composition, structure, and kinematics have been well studied, but details of their origins remain sketchy. The collapse of gas clouds, induced by external forces whereby gravity overcomes internal pressure to form stars, is the likely starting point. Among the perturbing initiators of galaxy formation, radio source beams (jets) are quite effective. Typically, a beam may spawn one galaxy, though instances of several aligned with the radio axis are known. Recently, we found an impressive 14 companions in the lobes of the giant radio galaxy DA 240, which we argue formed as the result of jet instigation. This conclusion is bolstered by the fact that the galaxy groups display Z-shaped symmetry with respect to the radio axis. There is some evidence for star formation among the aligned companions. We also conclude that galaxy alignments at low redshift may derive from line-emitting gas observed in radio components of high-redshift galaxies.

We propose a method to measure the time delay of the Five-hundred-meter Aperture Spherical radio Telescope (FAST) using baseband data and periodic noise injection. By applying a sliding time window and calculating the average standard deviation ratio over 1000 noise cycles, high-precision measurement of the noise-induced time delay is achieved. The proposed method offers several advantages, including a short recording duration, high measurement accuracy, and strong immunity to electromagnetic interference. It enables effective monitoring of hardware state changes in the signal chain, and provides technical support for the future participation of the FAST in radio interferometry.