PR Image eso1307b
The cluster NGC 6520 and the dark cloud Barnard 86 in the constellation of Sagittarius
Wide-field view of the star cluster NGC 6520 and the dark cloud Barnard 86
Infrared/visible-light crossfade view of the star cluster NGC 6520 and the dark cloud Barnard 86
Wide Field Imager snaps cosmic gecko
This image from the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile, shows the bright star cluster NGC 6520 and its neighbour, the strange gecko-shaped dark cloud Barnard 86. This cosmic pair is set against millions of glowing stars from the brightest part of the Milky Way — a region so dense with stars that barely any dark sky is seen across the picture.
This part of the constellation of Sagittarius (The Archer) is one of
the richest star fields in the whole sky — the Large Sagittarius Star
Cloud. The huge number of stars that light up this region dramatically
emphasise the blackness of dark clouds like Barnard 86, which appears at
the centre of this new picture from the Wide Field Imager, an
instrument mounted on the MPG/ESO 2.2-metre telescope at ESO’s La Silla
Observatory in Chile.
This object, a small, isolated dark nebula known as a Bok globule [1], was described as “a drop of ink on the luminous sky” by its discoverer Edward Emerson Barnard [2],
an American astronomer who discovered and photographed numerous comets,
dark nebulae, one of Jupiter’s moons, and made many other
contributions. An exceptional visual observer and keen
astrophotographer, Barnard was the first to use long-exposure
photography to explore dark nebulae.
Through a small telescope Barnard 86 looks like a dearth of stars, or
a window onto a patch of distant, clearer sky. However, this object is
actually in the foreground of the star field — a cold, dark, dense cloud
made up of small dust grains that block starlight and make the region
appear opaque. It is thought to have formed from the remnants of a
molecular cloud that collapsed to form the nearby star cluster NGC 6520,
seen just to the left of Barnard 86 in this image.
NGC 6520 is an open star cluster that contains many hot stars that
glow bright blue-white, a telltale sign of their youth. Open clusters
usually contain a few thousand stars that all formed at the same time,
giving them all the same age. Such clusters usually only live
comparatively short lives, on the order of several hundred million
years, before drifting apart.
The incredible number of stars in this area of the sky muddles
observations of this cluster, making it difficult to learn much about
it. NGC 6520’s age is thought to be around 150 million years, and both
this star cluster and its dusty neighbour are thought to lie at a
distance of around 6000 light-years from our Sun.
The stars that appear to be within Barnard 86 in the image above are
in fact in front of it, lying between us and the dark cloud. Although it
is not certain whether this is still happening within Barnard 86, many
dark nebulae are known to have new stars forming in their centres — as
seen in the famous Horsehead Nebula (eso0202), the striking object Lupus 3 (eso1303) and to a lesser extent in another of Barnard’s discoveries, the Pipe Nebula (eso1233).
However, the light from the youngest stars is blocked by the
surrounding dusty regions, and they can only be seen in infrared or
longer-wavelength light.
Notes
[1] Bok globules were first observed in
the 1940s by astronomer Bart Bok. They are very cold, dark clouds of
gas and dust that often have new stars forming at their centres. These
globules are rich in dust that scatters and absorbs background light, so
they are almost opaque to visible light.
[2] This quotation comes from E. E. Barnard, Dark
Regions in the Sky Suggesting an Obscuration of Light, Yerkes
Observatory, Nov 15 1913 (available online here).
More information
ESO, the European Southern Observatory, is
the foremost intergovernmental astronomy organisation in Europe and the
world’s most productive astronomical observatory. It is supported by 15
countries: Austria, Belgium, Brazil, the Czech Republic, Denmark,
France, Finland, Germany, Italy, the Netherlands, Portugal, Spain,
Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious
programme focused on the design, construction and operation of powerful
ground-based observing facilities enabling astronomers to make
important scientific discoveries. ESO also plays a leading role in
promoting and organising cooperation in astronomical research. ESO
operates three unique world-class observing sites in Chile: La Silla,
Paranal and Chajnantor. At Paranal, ESO operates the Very Large
Telescope, the world’s most advanced visible-light astronomical
observatory and two survey telescopes. VISTA works in the infrared and
is the world’s largest survey telescope and the VLT Survey Telescope is
the largest telescope designed to exclusively survey the skies in
visible light. ESO is the European partner of a revolutionary
astronomical telescope ALMA, the largest astronomical project in
existence. ESO is currently planning the 39-metre European Extremely
Large optical/near-infrared Telescope, the E-ELT, which will become “the
world’s biggest eye on the sky”.
Links
- Information about the MPG/ESO 2.2-metre telescope
- Information about the La Silla Observatory
- Images of La Silla
Contacts
Richard Hook
ESO, La Silla, Paranal, E-ELT and Survey Telescopes Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
ESO, La Silla, Paranal, E-ELT and Survey Telescopes Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
