Science colloqium of the CPS: Andrea Bracco: And Now for Something completely different: exploring interstellar magnetic fields in the Milky Way

Abstract: What would you say if you were asked: "What is the Milky Way made of?"
Most likely, and reasonably, "stars" would be the answer. However, not only stars
are just one facet of the Galactic content but modern astrophysics also struggles in
explaining the details of their formation process. In order to gain insights into
this problem it is key to study the physics of the outer space that fills the Galaxy
between stars, which is called interstellar medium. 

The interstellar medium is a plasma made of cosmic rays, multiphase gas, and dust
particles, all tightly coupled with magnetic fields. It is through their
interactions that a complex cycle, involving gravity, several phase transitions, and
magneto-hydrodynamic turbulence, leads diffuse/warm matter to condense into
denser/colder regions, where stars eventually form. However, the detailed processes
of this matter cycle are still unclear. For decades, one of the most difficult
challenges of astrophysical observations has been the characterization of magnetic
fields along this evolutionary sequence. 

Today, thanks to the technological breakthrough of new experiments, such as the
ESA-Planck satellite, we are now entering a new era to probe the magnetic properties
of the interstellar medium.  

After reviewing the state-of-the-art investigation of magnetic fields in the Milky
Way, in this talk I will give an introductive overview of the recent results
obtained by the Planck Consortium. Using unprecedented maps of linear polarization
at sub-millimeter wavelengths, for the first time, we were able to trace the
magnetic field structure of our own Galaxy over the whole sky. I will focus on
several aspects of our data analysis that show the relevance of magnetic fields in
the Galactic environment, from the diffuse medium to the regions where early star
formation takes place.

I will conclude my talk with interesting perspectives for the future to study the
magnetic properties of the Milky Way by combining multiple probes of the
interstellar medium with existing and upcoming experiments, such as Planck, LOFAR,
and SKA.