Copyright: ESA and the Planck Collaboration
This image from ESA’s Planck
satellite appears to show something quite ethereal and fantastical: a
sprite-like figure emerging from scorching flames and walking towards
the left of the frame, its silhouette a blaze of warm-hued colours.
This
fiery illusion is actually a celestial feature named the Polaris Flare.
This name is somewhat misleading; despite its moniker, the Polaris Flare
is not a flare but a 10 light-year-wide bundle of dusty filaments in
the constellation of Ursa Minor (The Little Bear), some 500 light-years
away.
The Polaris Flare is located near the North Celestial Pole,
a perceived point in the sky aligned with Earth’s spin axis. Extended
into the skies of the northern and southern hemispheres, this imaginary
line points to the two celestial poles. To find the North Celestial
Pole, an observer need only locate the nearby Polaris (otherwise known
as the North Star or Pole Star), the brightest star in the constellation
of Ursa Minor.
Some of the secrets of the Polaris Flare were uncovered when it was observed by ESA’s Herschel some years ago. Using a combination of such Herschel observations and a computer simulation, scientists think
that the Polaris Flare filaments could have been formed as a result of
slow shockwaves pushing their way through a dense interstellar cloud, an
accumulation of cold cosmic dust and gas sitting between the stars of
our Galaxy.
These shockwaves, reminiscent of the sonic booms
formed by fast sound waves here on Earth, would have been themselves
triggered by nearby exploding stars that disrupted their surroundings as
they died, triggering cloud-wide waves of turbulence.
These
shockwaves, reminiscent of the sonic booms formed by fast sound waves
here on Earth, were themselves triggered by nearby exploding stars that
disrupted their surroundings as they died, triggering cloud-wide waves
of turbulence. These waves swept up the gas and dust in their path,
sculpting the material into the snaking filaments we see.
This
image is not a true-colour view, nor is it an artistic impression of the
Flare, rather it comprises observations from Planck, which operated
between 2009 and 2013. Planck scanned and mapped the entire sky,
including the plane of the Milky Way,
looking for signs of ancient light (known as the cosmic microwave
background) and cosmic dust emission. This dust emission allowed Planck
to create this unique map of the sky – a magnetic map.
The relief
lines laced across this image show the average direction of our Galaxy’s
magnetic field in the region containing the Polaris Flare. This was
created using the observed emission from cosmic dust, which was
polarised (constrained to one direction). Dust grains in and around the
Milky Way are affected by and interlaced with the Galaxy’s magnetic
field, causing them to align preferentially in space. This carries
through to the dust’s emission, which also displays a preferential
orientation that Planck could detect.
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.
This frame has an area of 30 x 30º on the
sky, and the colours represent the intensity of dust emission.
Source: ESA/Space in Images
