It's a fingerprint... of the Milky Way

An international team of astrophysicists has released an unprecedented map of the entire sky that charts the magnetic field shaping our Milky Way Galaxy.

The map reveals magnetic field lines running parallel to the plane of the Galaxy, as well as great loops and whorls associated with nearby clouds of gas and dust.

The team – which includes researchers from the Canadian Institute for Theoretical Astrophysics (CITA) at the University of Toronto as well as the University of British Columbia – created the map using data from the Planck Space Telescope. Since 2009, Planck has charted the Cosmic Microwave Background (CMB), the light from the Universe a mere 380,000 years after the Big Bang.

But Planck also observes light from much closer than the farthest reaches of time and space. With an instrument called the High Frequency Instrument (HFI), Planck detects the light from microscopic dust particles within our Galaxy. (The density of this dust is incredibly low; a volume of space equal to a large sports stadium or arena would contain one grain.)

Planck’s HFI identifies the non-random direction in which the light waves vibrate – known as polarization. It is this polarized light that indicates the orientation of the field lines.

“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,” says team member Professor Douglas Scott (UBC). “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.”

For example, the magnetic field governs the coupling of the motions of gas and dust between stars, and so plays a role in star formation and the dynamics of cosmic rays.

“And now,” says Scott, “Planck has given us the most detailed picture of it yet.”

The “fingerprint” and other results are described in four papers released May 6 (links below) and to be published in the journal Astronomy & Astrophysics.

Professor Peter Martin (CITA) uses Planck data to study the dust found throughout our Galaxy. According to Martin, “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.”

Also, for cosmologists 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 CMB. In March 2014, scientists 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.

And according to Professor J. Richard Bond (CITA), “These results help us lift the veil of emissions from these tiny but pervasive Galactic dust grains which obscure a Planck goal of peering into the earliest moments of the Big Bang to find evidence for gravitational waves created in that epoch, as reported by BICEP2.”

Planck includes contributions from the Canadian Space Agency (CSA). The CSA funds two Canadian research teams that are part of the Planck science collaboration, and who helped develop both of Planck's complementary science instruments, the High Frequency Instrument (HFI) and the Low Frequency Instrument (LFI). Professors Bond of the University of Toronto (Director of Cosmology and Gravity at the Canadian Institute for Advanced Research) and Scott of the University of British Columbia lead the Canadian Planck team, which includes members from the University of Alberta, Université Laval and McGill University.