The bright star cluster Messier 7 in the constellation of Scorpius
**************************************
Videos
New ESO image of star cluster Messier 7
A new image from ESO’s La Silla Observatory in Chile shows the bright
star cluster Messier 7. Easily spotted with the naked eye close to the
tail of the constellation of Scorpius, it is one of the most prominent
open clusters of stars in the sky — making it an important astronomical
research target.
Messier 7, also known as NGC 6475, is a brilliant cluster of about
100 stars located some 800 light-years from Earth. In this new picture
from the Wide Field Imager on the MPG/ESO 2.2-metre telescope it stands
out against a very rich background of hundreds of thousands of fainter
stars, in the direction of the centre of the Milky Way.
At about 200 million years old, Messier 7 is a typical middle-aged open cluster,
spanning a region of space about 25 light-years across. As they age,
the brightest stars in the picture — a population of up to a tenth of
the total stars in the cluster — will violently explode as supernovae.
Looking further into the future, the remaining faint stars, which are
much more numerous, will slowly drift apart until they become no longer
recognisable as a cluster.
Open star clusters like Messier 7 are groups of stars born at almost
the same time and place, from large cosmic clouds of gas and dust in
their host galaxy. These groups of stars are of great interest to
scientists, because the stars in them have about the same age and
chemical composition. This makes them invaluable for studying stellar
structure and evolution.
An interesting feature in this image is that, although densely
populated with stars, the background is not uniform and is noticeably
streaked with dust. This is most likely to be just a chance alignment of
the cluster and the dust clouds. Although it is tempting to speculate
that these dark shreds are the remnants of the cloud from which the
cluster formed, the Milky Way will have made nearly one full rotation
during the life of this star cluster, with a lot of reorganisation of
the stars and dust as a result. So the dust and gas from which Messier 7
formed, and the star cluster itself, will have gone their separate ways
long ago.
The first to mention this star cluster was the mathematician and
astronomer Claudius Ptolemy, as early as 130 AD, who described it as a
“nebula following the sting of Scorpius”, an accurate description given
that, to the naked eye, it appears as a diffuse luminous patch against
the bright background of the Milky Way. In his honour, Messier 7 is
sometimes called Ptolemy’s Cluster. In 1764 Charles Messier included it
as the seventh entry in his Messier catalogue.
Later, in the 19th century, John Herschel described the appearance of
this object as seen through a telescope as a “coarsely scattered cluster
of stars” — which sums it up perfectly.
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 MPG/ESO 2.2-metre telescope
- Photos from the MPG/ESO 2.2-metre telescope
- Photos of La Silla
Contacts
Richard HookESO, Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Source: ESO
