Wide-field image of the sky around the Sculptor Dwarf Galaxy
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The Sculptor Dwarf Galaxy, pictured in
this new image from the Wide Field Imager camera, installed on the
2.2-metre MPG/ESO telescope at ESO’s La Silla Observatory, is a close
neighbour of our galaxy, the Milky Way. Despite their close proximity,
both galaxies have very distinct histories and characters. This galaxy
is much smaller and older than the Milky Way, making it a valuable
subject for studying both star and galaxy formation in the early
Universe. However, due to its faintness, studying this object is no easy
task.
The Sculptor Dwarf Galaxy — also known as the Sculptor Dwarf Elliptical or the Sculptor Dwarf Spheroidal — is a dwarf spheroidal galaxy, and is one of the fourteen known satellite galaxies orbiting the Milky Way [1]. These galactic hitchhikers are located close by in the Milky Way’s extensive halo,
a spherical region extending far beyond our galaxy’s spiral arms. As
indicated by its name, this galaxy is located in the southern
constellation of Sculptor
and lies about 280 000 light-years away from Earth. Despite its
proximity, the galaxy was only discovered in 1937, as its stars are
faint and spread thinly across the sky.
Although difficult to pick out, the Sculptor Dwarf Galaxy was among
the first faint dwarf galaxies found orbiting the Milky Way. The tiny
galaxy’s shape intrigued astronomers at the time of its discovery, but
nowadays dwarf spheroidal galaxies play a more important role in
allowing astronomers to dig deeply into the Universe’s past.
The Milky Way, like all large galaxies, is thought to have formed
from the build-up of smaller galaxies during the early days of the
Universe. If some of these small galaxies still remain today, they
should now contain many extremely old stars. The Sculptor Dwarf Galaxy
fits the bill as a primordial galaxy, thanks to a large number of
ancient stars, visible in this image.
Astronomers can determine the age of stars in the galaxy because
their light carries the signatures of only a small quantity of heavy
chemical elements. These heavy elements accumulate in galaxies with
successive generations of stars. A low level of heavy elements thus
indicates that the average age of the stars in the Sculptor Dwarf Galaxy
is high.
This quantity of old stars makes the Sculptor Dwarf Galaxy a prime
target for studying the earliest periods of star formation. In a recent
study, astronomers combined all the data available for the galaxy to
create the most accurate star formation history ever determined for a
dwarf spheroidal galaxy. This analysis revealed two distinct groups of
stars in the galaxy. The first, predominant group is the older
population, which is lacking in heavier elements. The second, smaller
population, in contrast, is rich with heavy elements. Like young people
crowding into city centres, this youthful stellar population is
concentrated toward the galaxy’s core.
The stars within dwarf galaxies like the Sculptor Dwarf Galaxy can
exhibit complex star formation histories. But as most of these dwarf
galaxies’ stars have been isolated from each other and have not
interacted for billions of years, each collection of stars has charted
its own evolutionary course. Studying the similarities in dwarf
galaxies’ histories, and explaining the occasional outliers, will help
to explain the development of all galaxies, from the most unassuming
dwarf to the grandest spirals. There is indeed much for astronomers to
learn from the Milky Way’s shy neighbours.
Notes
[1] This faint galaxy should not be confused with the much brighter Sculptor Galaxy (NGC 253) in the same constellation.
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 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”.
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
