The dwarf galaxy WLM in the constellation of Cetus
Wide-field view of the sky around the dwarf galaxy WLM
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Zooming in on the dwarf galaxy WLM
This scene, captured by ESO’s OmegaCAM on
the VLT Survey Telescope, shows a lonely galaxy known as
Wolf-Lundmark-Melotte, or WLM for short. Although considered part of our
Local Group of dozens of galaxies, WLM stands alone at the group’s
outer edges as one of its most remote members. In fact, the galaxy is so
small and secluded that it may never have interacted with any other
Local Group galaxy — or perhaps even any other galaxy in the history of
the Universe.
Rather like an uncontacted tribe living deep in the Amazon
rainforest or on an island in Oceania, WLM offers a rare insight into
the primordial nature of galaxies that have been little disturbed by
their environment.
WLM was discovered in 1909 by German astronomer Max Wolf, and identified as a galaxy some fifteen years later by astronomers Knut Lundmark and Philibert Jacques Melotte
— explaining the galaxy’s unusual moniker. The dim galaxy is located in
the constellation of Cetus (The Sea Monster) about three million
light-years away from the Milky Way, which is one of the three dominant
spiral galaxies in the Local Group.
WLM is quite small and lacks structure, hence its classification as a dwarf irregular galaxy.
WLM spans about 8000 light-years at its greatest extent, a measurement
that includes a halo of extremely old stars discovered in 1996 (eso9633).
Astronomers think that comparatively small primeval
galaxies gravitationally interacted with each other and in many cases
merged, building up into larger composite galaxies. Over billions of
years, this merging process assembled the large spiral and elliptical
galaxies that now appear to be common in the modern Universe.
Galaxies
congregating in this manner is similar to the way in which human
populations have shifted over thousands of years and intermixed into
larger settlements, eventually giving rise to today’s megacities.
WLM has instead developed on its own, away from the
influence of other galaxies and their stellar populations. Accordingly,
like a hidden human population with limited contact with outsiders, WLM
represents a relatively unperturbed “state of nature”, where any changes occurring over its lifetime have taken place largely independent of activity elsewhere.
This small galaxy features an extended halo of very dim red
stars, which stretches out into the inky blackness of the surrounding
space. This reddish hue is indicative of advanced stellar age. It is
likely that the halo dates back to the original formation of the galaxy
itself, helpfully offering clues about the mechanisms that spawned the
very first galaxies.
The stars at the centre of WLM, meanwhile, appear younger
and bluer in colour. In this image, pinkish clouds highlight areas where
the intense light from young stars has ionised ambient hydrogen gas, making it glow in a characteristic shade of red.
This detailed image was captured by the OmegaCAM wide-field imager, a huge camera mounted on ESO’s VLT Survey Telescope (VST)
in Chile — a 2.6-metre telescope exclusively designed to survey the
night sky in visible light. OmegaCAM’s 32 CCD detectors create
256-megapixel images, offering a very detailed wide-field view of the
cosmos.
More Information
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is the world’s largest survey telescope and the VLT Survey Telescope is
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building the 39-metre European Extremely Large Telescope, the E-ELT,
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Links
Contacts:
Richard Hook
ESO education and Public Outreach Department
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
ESO education and Public Outreach Department
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Source: ESO
