Map of the structure of polarised microwave emission in the northern hemisphere measured by QUIJOTE. The drapery pattern represents the direction of the galactic magnetic field. The colour scale represents the intensity of the emission. © QUIJOTE collaboration.

The QUIJOTE experiment has successfully mapped the structure of the magnetic field of our galaxy, the Milky Way

The QUIJOTE experiment is sited at the Teide Observatory (Izaña, Tenerife) and comprises two telescopes, each  2.25m in diameter, which observe the sky in the microwave range (10-40 GHz). Led by the Instituto de Astrofísica de Canarias (IAC), this experiment started observing in 2012.

Now, thanks to the data obtained with its multifrequency instrument (MFI), which was working until 2018, a team of scientists has presented a set of results, in six articles, that give the most accurate description of the structure of the polarisation in the microwave emission processes in the Milky Way.

José Alberto Rubiño, the scientist in charge of QUIJOTE, and principal investigator of the European project RADIOFOREGROUNDS, said: “These maps give a detailed description in a new frequency range, from 10 to 20 GHz, complementary to those from space missions that have previously observed the sky at microwaves, such as Planck (ESA) and WMAP (NASA).

“We have characterised the synchrotron emission from our galaxy with unprecedented accuracy.

“This radiation is the result of the emission by charged particles moving at velocities close to that of light within the galactic magnetic field.

“These maps, the result of almost 9,000 hours of observation, are a unique tool for studying magnetism in the universe.”

See also: Astronomers discovery hot gas bubble ‘swirling’ around Milky Way’s black hole

Teide observatory

The QUIJOTE experiment at the Teide Observatory (Tenerife, Spain) where the structure of the magnetic field has been mapped. © Daniel López/ IAC.

Polarised synchrotron radiation and the CMB

The cosmic background radiation is the fossil radiation that originated during the first instants of the universe, and which we observe today at radio wavelength.

This type of radiation is studied by scientists because “by studying the properties of its polarisation we hope to find an indirect clue to the existence of gravitational waves after the Big Bang,” Ricardo Génova-Santos (IAC), a member of the science team, explained.

To measure this signal from the origin of the universe, the scientists need to eliminate the veil of emission associated with the Milky Way. The new maps provided by QUIJOTE are a tool for performing this task.

Elena de la Hoz, a researcher at the Instituto de Física de Cantabria (IFCA), said: “One of the most interesting results we have found is that the polarised synchrotron emission from our galaxy is much more variable than had been thought.

“The results we have obtained are a reference to help future experiments make reliable detections of the cosmological signal.”

Rubiño added: “The detection of this cosmological signal, a very specific pattern in the polarisation of the microwave background associated with the presence of gravitational waves generated during the so-called inflationary epoch, opens a new window on fundamental physics, which will allow us to explore scales of energy billions of times bigger than those which we can explore on the ground using particle accelerators.

“Studying it will help us to understand the energetic processes that took place at the birth of the universe.”

anomalous microwave emission

The new data from QUIJOTE are also a unique tool for studying the anomalous microwave emission (AME), a type of emission first detected 25 years ago, which is thought to be produced by the rotation of very small particles of dust in the interstellar medium, which tend to be aligned by the presence of the galactic magnetic field. 

Frédérick Poidevin, a researcher at the IAC, said: “The polarisation properties of these emissions must be characterised and understood in detail in order to decontaminate maps of the polarisation of the CMB, leaving them free to study cosmology.”

And Denis Tramonte a researcher at the Purple Mountain Observatory (PMO-CAS, China), explained: “Using the new results from QUIJOTE we have improved our understanding of the AME in numerous regions of our galaxy.”

The maps from QUIJOTE have also permitted the study of the microwave emission from the centre of our galaxy. Recently an excess of microwave emission has been detected from this region, whose origin is unknown, but whose origin could be connected to the decay processes of dark matter particles.

Federica Guidi, a researcher at the Institut d’Astrophysique de Paris  (IAP, France), said: “With QUIJOTE we have confirmed the existence of this excess of radiation, and have found some evidence that it could be polarised.

The articles are published in Monthly Notices of the Royal Astronomical Society.