Star formation and magnetic turbulence in the Orion Molecular Cloud
Copyright: ESA and the Planck Collaboration. Hi-res JPG
An
annotated version of the image can be found here
With blue hues suggestive of marine paradises and a texture evoking
the tranquil flow of sea waves, this image might make us daydream of
sandy beaches and exotic holiday destinations. Instead, the subject of
the scene is intense and powerful, because it depicts the formation of
stars in the turbulent billows of gas and dust of the Orion Molecular
Cloud.
The image is based on data from ESA’s Planck satellite,
which scanned the sky between 2009 and 2013 to study the cosmic
microwave background, the most ancient light in the Universe’s history.
While doing so, Planck also detected foreground emission from material
in the Milky Way, as well as from other galaxies.
Our Galaxy is
pervaded by a diffuse mixture of gas and dust that occasionally becomes
denser, creating giant gas clouds where stars can form. While present
only in traces, dust is a crucial ingredient in these interstellar
clouds. It also shines brightly at some of the wavelengths that were
probed by Planck, so astronomers can use these data to learn more about
the cradles of star formation.
In addition, dust grains have
elongated shapes and tend to align their longest axis at right angles to
the direction of the Galaxy’s magnetic field. This makes their emission
partly ‘polarised’ – it vibrates in a preferred direction. Since Planck
was equipped with polarisation-sensitive detectors, its scans also
contain information about the direction of the magnetic field threading
the Milky Way.
This image combines a visualisation of the total
intensity of dust emission, shown in the colour scale, with an
indication of the magnetic field’s orientation, represented by the
texture. Blue hues correspond to regions with little dust, while the
yellow and red areas reflect denser (and mostly hotter) clouds
containing larger amounts of dust, as well as gas.
The red clumps
at the centre of the image are part of the Orion Molecular Cloud
Complex, one of the closest large regions of star formation, only about
1300 light-years from the Sun. The most prominent of the red clumps, to
the lower left of centre, is the famous Orion Nebula, also known as M42.
This is visible to the naked eye in the constellation Orion, just below
the three stars forming the ‘belt’ of the mythological hunter.
The
magnetic field appears regular and organised in almost parallel lines
in the upper part of the image: this is a result of the large-scale
arrangement of the magnetic field along the Galactic plane, which is
located above the top of this image. However, the field becomes less
regular in the central and lower parts of the image, in the region of
the Orion Molecular Cloud. Astronomers believe that the turbulent
structure of the magnetic field observed in this and other star-forming
clouds is related to the powerful processes taking place when stars are
being born.
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. The
image spans about 40ยบ across.
Source: ESA
