HUBBLE IMAGES SAGITTARIUS
This new image from the Hubble Space Telescope
shows a small galaxy
called the Sagittarius dwarf irregular galaxy, or
"SagDIG" for short.
SagDIG is relatively nearby, and Hubble's sharp
vision is able to reveal
many thousands of individual stars within the galaxy.
The brightest stars in the picture (easily distinguished
by the spikes
radiating from their images, produced by optical
effects within the
telescope), are foreground stars lying within our
own Milky Way galaxy.
Their distances from Earth are typically a few thousand
By contrast, the numerous faint, bluish stars belong
to SagDIG, which
lies some 3.5 million light-years (1.1 Megaparsecs)
from us. Lastly,
background galaxies (reddish/brown extended objects
with spiral arms
and halos) are located even further beyond SagDIG
at several tens of
millions parsecs away.
As their name implies, dwarf irregular galaxies
are unlike their spiral
and elliptical cousins, because of their much smaller
physical size and
lack of definite structure. Using Hubble, astronomers
are able to resolve
dwarf irregular galaxies that are at very large
distances from Earth,
into individual stars. By examining properties of
the galaxy, such as
distance, age and chemical composition, the star
formation history of the
whole galaxy is better understood, and reveals how,
where, and when active
star formation took place.
The main body of SagDIG shows a number of star-forming
complexes that cover an appreciable fraction of
the galaxy surface area. The presence of on-going
star formation in a gas-rich galaxy such as this
makes SagDIG an excellent laboratory where scientists
can test present-day theories of what triggers star-formation
in galaxies (without companions) and how this propagates
throughout the galaxy.
This dwarf irregular galaxy was observed by the
Advanced Camera for Surveys on-board the Hubble
Space Telescope in August 2003. Fifty-minute exposures
were taken in blue, green and red filters. This
program marks an international collaboration between
Italian (Yazan Momany, Enrico V. Held, and Marco
Gullieuszik), E.S.O. (Ivo Saviane and Luigi Bedin),
U.S.A. (Michael Rich, Luca Rizzi), and Dutch (Konrad
Kuijken) institutions. This image was produced by
the Hubble Heritage Team (STScI/AURA).
Credit: NASA, ESA, and The Hubble Heritage Team
Acknowledgment: Y. Momany (University of Padua)
Learn more about an Asteroid
Trail found on this image...