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This new image from the VLT Survey
Telescope (VST) at ESO’s Paranal Observatory in Chile captures a
spectacular concentration of galaxies known as the Fornax Cluster, which
can be found in the southern hemisphere constellation of Fornax (The
Furnace). The cluster plays host to a menagerie of galaxies of all
shapes and sizes, some of which are hiding secrets.
Galaxies, it seems, are sociable animals and they like to gather together in large groups, known as clusters. Actually it’s gravity
that holds the galaxies in the cluster close together as a single
entity, with the pull of gravity arising from large amounts of dark
matter, as well as from the galaxies we can see. Clusters can contain
anything between about 100 and 1000 galaxies and can be between about 5
and 30 million light-years across.
Galaxy clusters do not come in neatly defined shapes so it is
difficult to determine exactly where they begin and end. However,
astronomers have estimated that the centre of the Fornax Cluster
is in the region of 65 million light-years from Earth. What is more
accurately known is that it contains nearly sixty large galaxies, and a
similar number of smaller dwarf galaxies.
Galaxy clusters like this one are commonplace in the Universe and
illustrate the powerful influence of gravity over large distances as it
draws together the enormous masses of individual galaxies into one
At the centre of this particular cluster, in the middle of the three
bright fuzzy blobs on the left side of the image, is what is known as a cD galaxy — a galactic cannibal. cD galaxies like this one, called NGC 1399, look similar to elliptical galaxies but are bigger and have extended, faint envelopes . This is because they have grown by swallowing smaller galaxies drawn by gravity towards the centre of the cluster .
Indeed, there is evidence that this process is happening before our
eyes — if you look closely enough. Recent work by a team of astronomers
led by Enrichetta Iodice (INAF – Osservatorio di Capodimonte, Naples,
using data from ESO’s VST, has revealed a very faint bridge of light
between NGC 1399 and the smaller galaxy NGC 1387 to its right. This
bridge, which has not been seen before (and is too faint to show up in
this picture), is somewhat bluer than either galaxy, indicating that it
consists of stars created in gas that was drawn away from NGC 1387 by
the gravitational pull of NGC 1399. Despite there being little evidence
for ongoing interactions in the Fornax Cluster overall, it seems that
NGC 1399 at least is still feeding on its neighbours.
Towards the bottom right of this image is the large barred spiral galaxy
NGC 1365. This is a striking example of its type, the prominent bar
passing through the central core of the galaxy, and the spiral arms
emerging from the ends of the bar. In keeping with the nature of cluster
galaxies, there is more to NGC 1365 than meets the eye. It is
classified as a Seyfert Galaxy, with a bright active galactic nucleus
also containing a supermassive black hole at its centre.
This spectacular image was taken by the VLT Survey Telescope (VST) at ESO’s Paranal Observatory
in Chile. At 2.6 metres in diameter, the VST is by no means a large
telescope by today’s standards, but it has been designed specifically to
conduct large-scale surveys of the sky. What sets it apart is its huge
corrected field of view and 256-megapixel camera, called OmegaCAM,
which was specially developed for surveying the sky. With this camera
the VST can produce deep images of large areas of sky quickly, leaving
the really big telescopes — like ESO’s Very Large Telescope (VLT) — to explore the details of individual objects.
 The image captures only the central regions of the Fornax Cluster; it extends over a larger region of sky.
 The central galaxy is often the brightest galaxy in a cluster, but in this case the brightest galaxy,NGC 1316,
is situated at the edge of the cluster, just outside the area covered
by this image. Also known as Fornax A, it is one of the most powerful
sources ofradio wavesin the sky. The radio waves, which can be seen byspecialised telescopessensitive to this kind of radiation, emanate from two enormous lobes
extending far into space either side of the visible galaxy. The energy
that powers the radio emission comes from asupermassive black holelurking at the centre of the galaxy which is emitting two opposing jets ofhigh-energy particles. These jets produce the radio waves when they plough into therarefied gaswhich occupies the space between galaxies in the cluster.
 “The Fornax Deep Survey with VST.
I. The extended and diffuse stellar halo of NGC1399 out to 192 kpc” by
E. Iodice, M. Capaccioli , A. Grado , L. Limatola, M. Spavone, N.R.
Napolitano, M. Paolillo, R. F. Peletier, M. Cantiello, T. Lisker, C.
Wittmann, A. Venhola , M. Hilker , R. D’Abrusco, V. Pota, and P.
Schipani has been published in the Astrophysical Journal.
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 16 countries: Austria, Belgium, Brazil, the
Czech Republic, Denmark, France, Finland, Germany, Italy, the
Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United
Kingdom, along with the host state of Chile. 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 a major partner in ALMA, the largest astronomical
project in existence. And on Cerro Armazones, close to Paranal, ESO is
building the 39-metre European Extremely Large Telescope, the E-ELT,
which will become “the world’s biggest eye on the sky”.