The Magellanic Clouds and an interstellar filament
Copyright: ESA and the Planck Collaboration
Portrayed in this image from ESA’s Planck satellite are the two
Magellanic Clouds, among the nearest companions of our Milky Way galaxy.
The Large Magellanic Cloud, about 160 000 light-years away, is the
large red and orange blob close to the centre of the image. The Small
Magellanic Cloud, some 200 000 light-years from us, is the vaguely
triangular-shaped object to the lower left.
At around ten and
seven billion times the mass of our Sun, respectively, these are classed
as dwarf galaxies. As a comparison, the Milky Way and another of its
neighbours, the Andromeda galaxy, boast masses of a few hundred billion
solar masses each.
The Magellanic Clouds are not visible from high
northern latitudes and were introduced to European astronomy only at
the turn of the 16th century. However, they were known long before by
many civilisations in the southern hemisphere, as well as by Middle
Eastern astronomers.
Planck detected the dust between the stars
pervading the Magellanic Clouds while surveying the sky to study the
cosmic microwave background – the most ancient light in the Universe –
in unprecedented detail. In fact, Planck detected emission from
virtually anything that shone between itself and the cosmic background
at its sensitive frequencies.
These foreground contributions
include many galaxies, near and far, as well as interstellar material in
the Milky Way. Astronomers need to remove them in order to access the
wealth of cosmic information contained in the ancient light. But, as a
bonus, they can use the foreground observations to learn more about how
stars form in galaxies, including our own.
Interstellar dust from
the diffuse medium that permeates our Galaxy can be seen as the mixture
of red, orange and yellow clouds in the upper part of this image, which
belong to a large star-forming complex in the southern constellation,
Chameleon.
In addition, a filament can also be seen stretching
from the dense clouds of Chameleon, in the upper left, towards the
opposite corner of the image.
Apparently located between the two
Magellanic Clouds as viewed from Planck, this dusty filament is in fact
much closer to us, only about 300 light-years away. The image shows how
well this structure is aligned with the galaxy’s magnetic field, which
is represented as the texture of the image and was estimated from
Planck’s measurements.
By comparing the structure of the magnetic
field and the distribution of interstellar dust in the Milky Way,
scientists can study the relative distribution of interstellar clouds
and the ambient magnetic field. While in the case of the filamentary
cloud portrayed in this image, the structure is aligned with the
direction of the magnetic field, in the denser clouds where stars form
filaments tend to be perpendicular to the interstellar magnetic field.
The
lower right part of the image is one of the faintest areas of the sky
at Planck’s frequencies, with the blue hues indicating very low
concentrations of cosmic dust. Similarly, the eddy-like structure of the
texture is caused primarily by instrument noise rather than by actual
features in the magnetic field.
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.
Source: ESA
