You’re Looking at a Map of the Milky Way’s Magnetic Field

Using telescopes that study the sky in the microwave part of the electromagnetic spectrum, astronomers have successfully mapped the structure of the magnetic field of the Milky Way galaxy. While magnetic fields are difficult to measure in space, an international team of astronomers used the Teide Observatory on Tenerife in the Canary Islands to conduct 10 years of observations.

The team’s collaboration, called QUIJOTE (Q-U-I JOint TEnerife) used two 2.5 m diameter telescopes, to observe the sky in the microwave part of the electromagnetic spectrum. Learning more about our galaxy’s magnetic field can provide information about star formation, cosmic rays, and many other  astrophysical processes.

The team said their work complements data gathered by previous space missions dedicated to the study of the cosmic microwave background radiation (CMB), the fossil radiation left behind by the Big Bang, which gave a detailed insight into the early history of the cosmos.

“These new maps give a detailed description in a new frequency range, from 10 to 40 GHz, complementing those from space missions such as Planck and WMAP,” said José Alberto Rubiño, lead scientist of the QUIJOTE Collaboration, in a press release. “We have characterized 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.”

The work on this mapping project started in 2012, and the team has now published a series of 6 scientific papers that provide the most accurate description to date of the polarization of the emission of the Milky Way at microwave wavelengths. Polarization is a “property of transverse waves such as light waves that specifies the direction of the oscillations of the waves and signifies the presence of a magnetic field,” the team explained.

With the new maps, astronomers not only have more detailed information about the structure of the Milky Way’s magnetic field, but their findings also is helping to understand the energetic processes which took place close to the birth of the Universe.

“Scientific evidence suggests that the Universe went through a phase of rapid expansion, called inflation, a fraction of a second after the Big Bang,” said Rubiño. “If this is correct, we would expect to find some observable consequences when we study the polarization of the cosmic microwave background. Measuring those expected features is difficult, because they are small in amplitude, but also because they are less bright than the polarized emission from our own galaxy. However, if we finally measure them, we will have indirect information of the physical conditions in the very early stages of our Universe, when the energy scales were much higher than those that we can access or study from the ground. This has enormous implications for our understanding of fundamental physics.”

The new maps from QUIJOTE have also provided new data for studying a recently detected excess of microwave emission from the center of our Galaxy. The origin of this emission is currently unknown, but it could be connected to the decay processes of dark matter particles.

Additionally, the data from the  QUIJOTE collaboration allows scientists to  study over 700 sources of emission in radio and microwaves, of both Galactic and extragalactic origin, meaning that the data is helping scientists to decipher signals coming from beyond our galaxy, including the cosmic microwave background radiation.

 “One of the most interesting results we have found is that the polarized synchrotron emission from our Galaxy is much more variable than had been thought” said Elena de la Hoz, a researcher at the Instituto de Física de Cantabria (IFCA). “The results we have obtained are a reference to help future experiments make reliable detections of the CMB signal.

Below are links to the 6 papers published in the Monthly Notices of the Royal Astronomical Society:

• ‘QUIJOTE scientific results – IV. A northern sky survey in intensity and polarization at 10–20 GHz with the Multi-Frequency Instrument’, Rubiño-Martin et al.
• “The microwave intensity and polarization spectra of the Galactic regions W49, W51, and IC443”, Tramonte et al.
• “The Haze as seen by QUIJOTE”, Guidi et al.
• “Galactic AME sources in the QUIJOTE-MFI North Hemisphere wide survey”, Poidevin et al.
• “Diffuse polarized foregrounds from component separation with QUIJOTE-MFI”, de la Hoz et al.
• “Radio sources in the QUIJOTE-MFI wide survey maps”, Herranz et al.