Massive stars produce powerful outflows in the form of stellar winds that play a key role in chemically enriching the ISM and injecting mechanical energy into it. These hypersonic winds produce strong shock waves at which relativistic particles can be accelerated. This leads to a rich phenomenology in different astronomical scenarios, as the ones listed below.

In this context, I am a member of the PANTERA-STARs collaboration.

These systems contain (at least) two massive stars, each with its own stellar wind. These winds collide with each other, producing strong shocks that can heat the plasma to temperatures above 10⁷ K and also accelerate relativistic particles (most likely via diffusive shock acceleration). During my PhD I developed a multi-zone non-thermal emission model for massive colliding-wind binaries (del Palacio+ 2016). I have used this model to interpret the observed radio emission from systems like HD 93129A and Apep (del Palacio+ 2022), and also to predict their high-energy emission in hard X-rays and gamma-rays. This has allowed me to lead observational campaigns using X-ray satellites (Chandra and NuSTAR) to search for the elusive inverse Compton emission in HD 93129A (del Palacio+ 2020) and Apep (del Palacio+ 2023). The main goal of these and other related works is to infer physical parameters from these systems, such as the particle acceleration efficiency and magnetic field strength in the shocks, the mass-loss rate of the stars, or the spatial orientation of the system (provided that VLBI observations have already resolved the radio emission, which is then compared with synthetic emission maps from the model). I am also PI of an ALMA project to study Apep with high-resolution observations in Bands 6 and 7.

I have also contributed to polarimetric studies using observations with the JVLA to investigate the topology of the magnetic fields in the wind shocks (e.g. Hales+ 2017).

When stars move at a supersonic velocity, they produce a bow shock. I presented a multi-zone non-thermal emission model in del Palacio+ 2020, which was further developed in Martínez+ 2022 to include the emission from the forward shock (relevant for hypervelocity stars). More recently, in Martínez+ 2024 we expanded the model to account for thermal free-free emission as well. 

In progress.

Radio quiet active galactic nuclei (RQ AGN)

I have been studying the emission from AGNs that do not launch powerful jets. There is now very strong evidence of synchrotron emission being produced in the hot corona around the SMBH, which peaks at millimeter waves. In my most recent work, I have presented a method for disentangling this coronal component and measuring its main properties (magnetic field strength, size, non-thermal particle content). This model has been applied in the study of variable emission in IC 4329A (Shablobinskaya+ 24) and to interpret the spectral energy distribution of NGC 1068 (Mutie +25). 

More applications are on its way!