Galaxy’s petal-like structures came from collision

Not too long ago, galaxy PGC 6240, shown in a Hubble Space Telescope image, probably slammed into another huge swirl of stars, gas and dust. Such a cosmic crash would have shot ripples of energy through the galaxies, completely destroying their original structures. It could also have sparked star formation both within galaxies and in the regions of space around them, astronomers say.

Scientists have closely studied PGC 6240, which sits 350 million light-years from Earth in the southern constellation Hydrus, to piece together the events leading up to and immediately after a galactic collision.

PGC 6240 emerged from the likely crash sporting concentric, petal-like shells that sweep out from the galaxy. Combined, the shells give the galaxy its elliptical shape.                                                              

Swirling about the galaxy’s shells are globular clusters, groups of stars that are densely packed and gravitationally bound to each other. Most galaxies have such clusters orbiting them; the clusters tend to form at about the same time, meaning the stars are all about the same age. Some of PGC 6240’s clusters contain only old stars. But others are made of young stars, which suggests to astronomers that a relatively recent cosmic crash sparked new stars to form.