The Milky Way’s magnetic field


The galactic field lines paint a picture of one of the forces that has shaped the Milky Way.


The magnetic field along the galactic plane.
The magnetic field along the galactic plane.
ESA / Planck

Despite appearances, this image is not a Van Gogh but rather a visualisation of interactions between interstellar dust in the Milky Way and the galaxy’s magnetic field.

The European Space Agency’s Planck satellite scanned the skies over the years 2009 to 2013 to measure the cosmic microwave background, the radiation left over from just after the Big Bang. To see those background microwaves, it had to filter out a lot of emissions in the foreground caused by interstellar dust and gas in our own galaxy.

Astronomers can tell which emissions come from this gas and dust because they are partly polarised – the dust and gas prefers to vibrate in the direction of the field lines in the Milky Way’s magnetic field – and by mapping the emissions they can map the magnetic field itself.

The colour scale in the image represents the total intensity of dust emission, revealing the structure of interstellar clouds in the Milky Way. The texture is based on measurements of the direction of the polarised light emitted by the dust, which in turn indicates the orientation of the magnetic field.

The arrangement of the magnetic field is more ordered along the galactic plane, where it follows the spiral structure of the Milky Way. Small clouds are seen just above and below the plane, where the magnetic field structure becomes less regular.

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