Milky Way’s Magnetic Fingerprint Revealed

Astronomers using data from ESA’s Planck Space Telescope have created a map of the entire sky that charts the magnetic field shaping our Milky Way Galaxy.

Magnetic field of Milky Way Galaxy as seen by ESA’s Planck Space Telescope. Image credit: ESA / Planck Collaboration.

Light is a very familiar form of energy and yet some of its properties are all but hidden to everyday human experience. One of these, polarization, carries a wealth of information about what happened along a light ray’s path.

Light can be described as a series of waves of electric and magnetic fields. Usually, these fields can vibrate at all orientations. However, if they happen to vibrate preferentially in certain directions, scientists say the light is polarized.

In space, the light emitted by stars, gas and dust can also be polarized in various ways. By measuring the amount of polarization in this light, astronomers can study the physical processes that caused the polarization. In particular, polarization may reveal the existence and properties of magnetic fields in the medium light has traveled through.

In order to detect the light from microscopic dust particles within our Galaxy, scientists from the Planck Collaboration used an instrument called the High Frequency Instrument aboard the space telescope.

“Just as the Earth has a magnetic field, our Galaxy has a large-scale magnetic field – albeit 100,000 times weaker than the magnetic field at the Earth’s surface. And just as the Earth’s magnetic field generates phenomena such as the aurorae, our Galaxy’s magnetic field is important for many phenomena within it,” said team member Prof Douglas Scott from the University of British Columbia, who is a co-author of four papers submitted for publication in the journal Astronomy & Astrophysics (paper 1, paper 2, paper 3 and paper 4).

“Dust is often overlooked but it contains the stuff from which terrestrial planets and life form. So by probing the dust, Planck helps us understand the complex history of the Galaxy as well as the life within it,” said team member Dr Peter Martin from the University of Toronto’s Canadian Institute for Theoretical Astrophysics.

Also, for scientists studying the origin and evolution of the Universe, data to be released later this year by scientists from the Planck collaboration should allow astronomers to separate with great confidence any possible foreground signal from our Galaxy from the tenuous, primordial, polarized signal from the Cosmic Microwave Background.

In March, astronomers from the BICEP2 collaboration claimed the first detection of such a signal. The Planck data will enable a much more detailed investigation of the early history of the cosmos, from the accelerated expansion when the Universe was much less than one second old to the period when the first stars were born, several hundred million years later.