A Soft-Shell Galaxy

With Unusual Orbiting Clusters

The beautiful, petal-like shells of galaxy PGC 6240 are captured here in intricate detail by the NASA/ESA Hubble Space Telescope, set against a sky full of distant background galaxies.Courtesy NASA/ESA Hubble Space Telescope.

Ever wonder what a galaxy would look like some millions of years after it collided with another one?  Hubble Space Telescope captured a view of the distant galaxy PGC 6240 and it’s a very unusual-looking site. There’s a bright core surrounded by petal-like shells of material. The petals of this elliptical galaxy appear to be tightly wound in some areas and much more open and spread out in others. The most distant petals of material look like they are detached wings, heading out to space.

The strange petal layers aren’t the only thing unusual about this galaxy. It also has a collection of globular clusters that range in age from very old to very young. This is odd because most galaxies (including the Milky Way) have collections of globulars that all formed at about the same time. This galaxy’s clusters are all over the map, age-wise.

So, how could such an amazing vision of galactic  loveliness be created?  The best suggestion for how the galaxy’s stacked shell structure came into being and the existence of unexpectedly young globulars alongside clusters with much older stars is a galactic collision.

At some point in the past, PGC 6240 merged with another galaxy. An interaction of two galaxies is a gravitati0nal dance that displaces stars and nebulae and warps the shape of the galaxies that are merging. It sends ripples through the galaxy and eventually it disrupt the galactic structure. In this case, the interaction formed concentric shells of material.

Another byproduct of galaxy merger is bursts of star formation in the galaxy. Massive numbers of new stars were created in this collision leading to the creation of new, younger globular clusters around PGC 6240. They would orbit the galaxy, along with older globular clusters that formed when the galaxy was first born.

Galaxy collisions create fascinating structures out of two or more galaxies. Interactions and collisions are how most galaxies grow and evolve, a process that began billions of years ago with the first galaxies and continues to this day.


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