The star formation region NGC 6559 in the constellation of Sagittarius
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The Danish 1.54-metre telescope located
at ESO’s La Silla Observatory in Chile has captured a striking image of
NGC 6559, an object that showcases the anarchy that reigns when stars
form inside an interstellar cloud.
NGC 6559 is a cloud of gas and dust located at a distance of about
5000 light-years from Earth, in the constellation of Sagittarius (The
Archer). The glowing region is a relatively small object, just a few
light-years across, in contrast to the one hundred light-years and more
spanned by its famous neighbour, the Lagoon Nebula (Messier 8, eso0936).
Although it is usually overlooked in favour of its distinguished
companion, NGC 6559 has the leading role in this new picture.
The gas in the clouds of NGC 6559, mainly hydrogen, is the raw
material for star formation. When a region inside this nebula gathers
enough matter, it starts to collapse under its own gravity. The centre
of the cloud grows ever denser and hotter, until thermonuclear fusion
begins and a star is born. The hydrogen atoms combine to form helium
atoms, releasing energy that makes the star shine.
These brilliant hot young stars born out of the cloud energise the hydrogen gas still present around them in the nebula [1].
The gas then re-emits this energy, producing the glowing threadlike red
cloud seen near the centre of the image. This object is known as an
emission nebula.
But NGC 6559 is not just made out of hydrogen gas. It also contains
solid particles of dust, made of heavier elements, such as carbon, iron
or silicon. The bluish patch next to the red emission nebula shows the
light from the recently formed stars being scattered — reflected in many
different directions — by the microscopic particles in the nebula.
Known to astronomers as a reflection nebula, this type of object usually
appears blue because the scattering is more efficient for these shorter
wavelengths of light [2].
In regions where it is very dense, the dust completely blocks the
light behind it, as is the case for the dark isolated patches and
sinuous lanes to the bottom left-hand side and right-hand side of the
image. To look through the clouds at what lies behind, astronomers would
need to observe the nebula using longer wavelengths that would not be
absorbed.
The Milky Way fills the background of the image with countless
yellowish older stars. Some of them appear fainter and redder because of
the dust in NGC 6559.
This eye-catching image of star formation was captured by the Danish
Faint Object Spectrograph and Camera (DFOSC) on the 1.54-metre Danish
Telescope at La Silla in Chile. This national telescope has been in use
at La Silla since 1979 and was recently refurbished to turn it into a
remote-controlled state-of-the-art telescope.
Notes
[1] These young stars are usually of
spectral type O and B, with temperatures between 10 000 and 60 000 K,
which radiate huge amounts of high energy ultraviolet light that ionises
the hydrogen atoms.
[2] Rayleigh scattering, named after the British
physicist Lord Rayleigh, happens when light is scattered off particles
of material that are much smaller than the wavelength of the light. It
is much more effective for short wavelengths of light, that is,
wavelengths corresponding to the blue end of the visible spectrum, so
the result is a bluish diffuse light. This is the same mechanism that
explains the blue colour of the daytime cloud-free sky.
More information
ESO is the foremost intergovernmental
astronomy organisation in Europe and the world’s most productive
ground-based astronomical observatory by far. 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
- Photos of the Danish telescope
- Photos taken with the Danish telescope
- ESO press releases with results from the Danish telescope
Contacts
Richard HookESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
