PGC 6240 is an elliptical galaxy that resembles a pale rose in the sky, with hazy shells of stars encircling a very bright center. Some of these shells are packed close to the center of the galaxy, while others are flung further out into space. Several wisps of material have been thrown so far that they appear to be almost detached from the galaxy altogether.
All the globular clusters around a certain galaxy form at approximately
the same time, giving them all the same age. This is echoed within the
clusters -- all the stars within a single cluster form at around the
same time, too. Because of this, most galaxies have cluster populations
of pretty similar ages, both in terms of overall cluster, and individual
stars. However, PGC 6240 is unusual in that its clusters are varied --
while some do contain old stars, as expected, others contain younger
stars which formed more recently.
The most likely explanation for both the galaxy's stacked shell
structure and the unexpectedly young star clusters is that PGC 6240
merged with another galaxy at some point in the recent past. Such a
merger would send ripples through the galaxy and disrupt its structure,
forming the concentric shells of material seen here. It would also
ignite a strong burst of star formation in the galaxy, which would then
trigger similar activity in nearby space -- leading to the creation of
new, younger globular clusters around PGC 6240.
PGC 6240 is an elliptical galaxy in the southern constellation of Hydrus
(The Water Snake). Also visible in this region are numerous background
galaxies, speckled across the sky behind PGC 6240. Even though these
bodies are at such vast distances from us, it is possible to make out
the structure of many of the galaxies, especially the small spirals that
stand out colorfully against the dark sky.