ARTICLES
A Giant ‘Singing’ Cloud in space will Help us to Understand how
Star Systems Form
By Aris Tritsis
We know that the birthplaces of stars are large molecular clouds
of gas and dust found in space, but what exactly determines the
number and kind of stars and planets that are formed in these
clouds? How was our Solar system nursed and how did it emerge
from such a cloud billions of years ago? These are mysteries
that have been puzzling astronomers for decades, but research
recently published in “Science” adds an extra dimension to our
understanding. Trapped waves act like a fingerprint – they are unique and can
be used to identify the sizes of the boundaries that trapped them.
Boundaries are naturally created at the edges of clouds where
their physical properties change abruptly.
A 3D approach A ‘song’ in the cloud
Just like a cello and a violin make very distinct sounds, clouds
with different sizes and structures will vibrate in very different
manners – they will “sing” different “songs”.
Knowledge of the 3-dimensional structure of these clouds would
be an important leap in our understanding of how stars and
planets are born. The physics responsible for the formation of
stars is also responsible for shaping the clouds. But even with
the most advanced telescopes in the world we can only see the
two-dimensional projections of clouds on the plane of the sky.
By using this concept and calculating the frequencies seen in
observations of Musca it was possible to measure for the first
time the third dimension of the cloud, the one that extends along
our line of sight. The frequencies found in the observations were
scaled to the frequency range of human hearing to produce the
“song of Musca”.
Thankfully, there is a way around this problem. A recently
discovered type of structure in molecular clouds, called striations,
was found to form because of waves.
Here enters Musca, a molecular cloud that “sings”. Musca is an
isolated cloud in the Southern sky, below the Southern Cross, that
looks like a thin needle (see image on the right). It is hundreds of
light years away and stretches about 27 light years across, with a
depth of about 20 light years and width up to a fraction of a light
year.
Musca is surrounded by ordered hair-like striations produced by
trapped waves of gas and dust caused by the global vibrations
of the cloud.
The dark band is the Dark Doodad Nebula, a place where new
stars and planets can form. Flickrcafuego, CC BY-SA
The results from this method were amazing. Despite the fact that
Musca looks like a thin cylinder from Earth, the true size of its
hidden dimension is not small at all. In fact, it is comparable to its
largest visible dimension on the plane of the sky.
3D model of Musca molecular cloud. Aris Tritsis, ANU, Author
provided
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SCIENCE EDUCATIONAL NEWS VOL 67 NO 3