The magnetic field along the Galactic plane
Copyright: ESA/Planck Collaboration.
Acknowledgment: M.-A. Miville-Deschênes, CNRS – Institut d’Astrophysique Spatiale, Université Paris-XI, Orsay, France
Hi-Res Image (5.58 MB)
While the pastel tones and fine texture of this image may bring to mind
brush strokes on an artist’s canvas, they are in fact a visualisation of
data from ESA’s Planck satellite. The image portrays the interaction
between interstellar dust in the Milky Way and the structure of our
Galaxy’s magnetic field.
Between 2009 and 2013, Planck scanned the sky to detect the most ancient light in the history of the Universe – the cosmic microwave background. It also detected significant foreground emission from diffuse material in our Galaxy which, although a nuisance for cosmological studies, is extremely important for studying the birth of stars and other phenomena in the Milky Way.
Among the
foreground sources at the wavelengths probed by Planck is cosmic dust, a
minor but crucial component of the interstellar medium that pervades
the Galaxy. Mainly gas, it is the raw material for stars to form.
Interstellar
clouds of gas and dust are also threaded by the Galaxy’s magnetic
field, and dust grains tend to align their longest axis at right angles
to the direction of the field. As a result, the light emitted by dust
grains is partly ‘polarised’ – it vibrates in a preferred direction –
and, as such, could be caught by the polarisation-sensitive detectors on
Planck.
Scientists in the Planck collaboration are using the
polarised emission of interstellar dust to reconstruct the Galaxy’s
magnetic field and study its role in the build-up of structure in the
Milky Way, leading to star formation.
In this image, the colour
scale 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.
This
image shows the intricate link between the magnetic field and the
structure of the interstellar medium along the plane of the Milky Way.
In particular, 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.
From these and
other similar observations, Planck scientists found that filamentary
interstellar clouds are preferentially aligned with the direction of the
ambient magnetic field, highlighting the strong role played by
magnetism in galaxy evolution.
The emission from dust is computed
from a combination of Planck observations at 353, 545 and 857 GHz,
whereas the direction of the magnetic field is based on Planck
polarisation data at 353 GHz.
Source: ESA
