Six articles published in the journal “Monthly Notices of the Royal Astronomical Society” report various aspects of the most accurate mapping of the polarization of the Milky Way’s microwave emissions. This provides a map of the galactic magnetic field thanks to the QUIJOTE (Q-U-I JOint TEnerife) experiment. The QUIJOTE Collaboration presented what is only the initial set of scientific papers in a survey that complements the ones obtained from other missions such as the one from the Planck Surveyor satellite. These results are useful to obtain new information on the structure of the Milky Way’s magnetic field and to understand the energetic processes that occurred soon after the birth of the universe.
The image (Courtesy QUIJOTE Collaboration) shows the map of the polarized microwave emission measured by the QUIJOTE experiment. The line pattern shows the direction of the magnetic field lines. The color scale shows the intensity of the emissions. The lines are what give the image an effect similar to a Vincent Van Gogh painting.
Interstellar clouds of gas and dust are affected by the galactic magnetic field: the dust grains tend to align their long axis at right angles to the direction of the field. The consequence is that the light emitted by the dust grains is partially polarized and could be captured by polarization-sensitive instruments such as those of Planck, used to create a map of this type, or by the two telescopes of the QUIJOTE experiment at the Teide Observatory in Tenerife. That polarization can be exploited to study the Milky Way’s magnetic field.
The QUIJOTE experiment began observations in November 2012 by measuring polarization at frequencies between 10 GHz and 40 GHz, in the microwave band. About six years of observations allowed to collect data on the polarization of microwave emissions.
The data collected by the QUIJOTE experiment also made it possible to study what was called anomalous microwave emission (AME). First detected 25 years ago, it might be produced by the rotation of very small dust particles in the interstellar medium.
Any such study helps to understand the origins of various emissions from over 700 sources of radio waves and microwaves. The mapping obtained by the QUIJOTE experiment indicates that the Milky Way’s polarized synchrotron emission, generated by high-energy particles moving at speeds close to the speed of light in the galactic magnetic field, is much more variable than previously thought. Accurate detections help in the study of magnetism in galaxies and serve as a benchmark in future detections of the cosmic microwave background radiation that permeates the entire universe.
As for the center of the Milky Way, a higher-than-normal amount of microwave emissions was recently detected, and the cause of that increase is unknown. One possibility is that it’s related to the decay of dark matter particles, so the precise detections by the QUIJOTE experiment are also useful for testing dark matter models.
For such a large study, it’s inevitable that the six articles just published are only the beginning of the analysis of the results. Other articles are already in preparation and the data collected will continue to be examined, also together with those obtained in previous studies.