Understanding the magnetic field strength and morphology of astrophysical regions is of great importance in understanding their dynamics. There exist a number of methods astronomers can employ to trace magnetic field structures, and each have their own limitations. A promising technique to trace the magnetic field morphology around evolved stars, or on the smallest scales of (high-mass) star forming regions, is (sub-)millimeter spectral line polarization observations. Line (linear) polarization can either arise in association with maser radiative transfer, or alternatively, molecular lines polarize through the Goldreich-Kylafis effect. In both cases, the polarization angle traces the magnetic field with a 90-degree ambiguity. In order to remove this ambiguity, and to estimate the observational viability of particular line polarization measurements, polarized line radiative transfer needs to be employed.

In this talk, I present

(i) polarized radiative transfer tools that quantify the polarization of maser radiation,

(ii) a three-dimensional polarized line radiative transfer tool: PORTAL. PORTAL simulates the emergence of thermal molecular line polarization in astrophysical objects of arbitrary geometry and magnetic field morphology,

(iii) A novel polarization mechanism: collisional polarization. Which provides the possibility of directly detecting ambipolar diffusion in disks through the polarization of molecular ions,

and I will discuss observations of molecular line polarization around evolved stars andon the smallest scales of (high-mass) star forming regions.

Merging between galaxy clusters are the most energetic events in the Universe. Part of the energy released during these events is channeled into shocks and turbulence that accelerate particles in the Intra Cluster Medium (ICM) and produce diffuse cluster-scale radio emission. These sources have been studied for decades using observations at GHz-frequency, however, under many aspects, their origin remains unclear. Given the steepness of the spectrum of these sources, low frequency observations were the crucial, albeit missing, piece of the puzzle to understand these non-thermal phenomena. In this respect, the Low Frequency Array (LOFAR), recently opened a new frequency window (10-240 MHz) in the radio sky, which is the most promising window in this field. On one hand, this is leading to the discovery of new types of diffuse sources and physical interactions in the ICM, such as gently re-energised tails and even beyond the cluster-scale, such as bridges connecting pairs of galaxy clusters. On the other hand, thanks to the superior survey speed and sensitivity of LOFAR, we now have the possibility to analyse large samples of galaxy clusters, even in mass and redshift ranges that were previously inaccessible. In this talk, I will review some of the most important results that have been achieved in the past few years with LOFAR observations of galaxy clusters and I will discuss the ongoing and future work on the largest samples of clusters observed at low frequency.