The open star cluster NGC 6193 in the constellation of Ara
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This dramatic landscape in the southern
constellation of Ara (The Altar) is a treasure trove of celestial
objects. Star clusters, emission nebulae and active star-forming regions
are just some of the riches observed in this region lying some 4000
light-years from Earth. This beautiful new image is the most detailed
view of this part of the sky so far, and was taken using the VLT Survey
Telescope at ESO’s Paranal Observatory in Chile.
At the centre of the image is the open star cluster NGC 6193,
containing around thirty bright stars and forming the heart of the Ara
OB1 association. The two brightest stars are very hot giant stars.
Together, they provide the main source of illumination for the nearby
emission nebula, the Rim Nebula, or NGC 6188, which is visible to the right of the cluster.
A stellar association is a large grouping of loosely bound stars that
have not yet completely drifted away from their initial formation site.
OB associations consist largely of very young blue–white stars, which
are about 100 000 times brighter than the Sun and between 10 and 50
times more massive.
The Rim Nebula is the prominent wall of dark and bright clouds
marking the boundary between an active star-forming region within the
molecular cloud, known as RCW 108, and the rest of the association [1].
The area around RCW 108 is made up of mostly hydrogen — the primary
ingredient in star formation. Such areas are also known as H II regions.
The ultraviolet radiation and intense stellar wind from the stars of
NGC 6193 seem to be driving the next generation of star formation in the
surrounding clouds of gas and dust. As cloud fragments collapse they
heat up and eventually form new stars.
As the cloud creates new stars, it is simultaneously being eroded by
the winds and radiation emitted by previous stars, and by violent
supernova explosions. In this way, such star-forming H II regions tend
to have a lifespan of just a few million years. Star formation is a very
inefficient process, with only around 10% of the available material
contributing to the process — the rest is blown off into space.
The Rim Nebula also shows signs of being in the early phase of
“pillar formation”, meaning that in the future it could end up looking
similar to other well-known star-forming regions, such as the Eagle Nebula (Messier 16, containing the famous Pillars of Creation) and the Cone Nebula (part of NGC 2264).
This single spectacular image was actually created from more than 500
individual pictures taken through four different colour filters with
the VLT Survey Telescope. The total exposure time was more than 56
hours. It is the most detailed view of this region yet achieved.
Notes
[1] Furthermore, this nebula has additional modest fame among
astronomers, as a previous image was used as the cover of the DVD
distribution of the collection of software for astronomers assembled by
ESO: Scisoft, whose newest version was released a few weeks ago. It is therefore also known as the Scisoft Nebula.
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is the world’s largest survey telescope and the VLT Survey Telescope is
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Tel: +49 89 3200 6655
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Email: rhook@eso.org
Source: ESO
