Credit: NASA, ESA, and A. Sarajedini (University of Florida)
Acknowledgement: Gilles Chapdelaine
Acknowledgement: Gilles Chapdelaine
Named after its discoverer, the French-Armenian astronomer Agop
Terzan, this is the globular cluster Terzan 7 — a densely packed ball of
stars bound together by gravity. It lies just over 75 000 light-years
away from us on the other side of our galaxy, the Milky Way. It is a
peculiar cluster, quite unlike others we observe, making it an
intriguing object of study for astronomers.
Evidence shows that Terzan 7 used to belong to a small galaxy called the Sagittarius Dwarf Galaxy,
a mini-galaxy discovered in 1994. This galaxy is currently colliding
with, and being absorbed by, the Milky Way, which is a monster in size
when compared to this tiny one. It seems that this cluster has already
been kidnapped from its former home and now is part of our own galaxy.
Astronomers recently discovered that all the stars in Terzan 7 were
born at around the same time, and are about eight billion years old.
This is unusually young for such a cluster. The shared birthday is
another uncommon property; a large number of globular clusters, both in
the Milky Way and in other galaxies, seem to have at least two clearly
differentiated generations of stars that were born at different times.
Some explanations suggest that there is something different about
clusters that form within dwarf galaxies, giving them a different
composition. Others suggest that clusters like Terzan 7 only have enough
material to form one batch of stars, or that perhaps its youthfulness
has prevented it from yet forming another generation.
A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Gilles Chapdelaine.
Source: ESA/Hubble - Space Telescope
