You just have to make your way among the stars, and find it. This stunning Hubble Space Telescope image of PGC 6240, an elliptical galaxy in the southern constellation of Hydrus (the Water Snake) isn't just a strong candidate for your new desktop wallpaper — it's also an intriguing mystery.
The "pale rose" shape of this galaxy comes from its collection of globular clusters, which appear to be much younger than the galaxy itself. How did this happen? As the Hubble Space Telescope site explains:
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.
But we'll probably know more when we go there and see for ourselves. [SpaceTelescope.org]