Hubble Probes Possible Galaxy Merger :: NASANET

This image from the NASA/ESA Hubble Space Telescope shows the irregular dwarf galaxy NGC 5238, located 14.5 million light-years from Earth in the constellation Canes (The Dogs of Venice). Its dim, teardrop-shaped appearance is more reminiscent of a large star cluster than a classic image of a galaxy. Its dim appearance belies its complex structure, which has been the subject of much research. As the image shows, Hubble is able to discern the galaxy’s countless stars, as well as their associated globular clusters: bright spots in and around the galaxy filled with even more stars.

Astronomers believe that NGC 5238 may have collided with another galaxy just a billion years ago. The distorted shape of NGC 5238 is evidence of this interaction. When the two galaxies interacted, their gravity caused distortions in the distribution of stars in each galaxy. There is no nearby galaxy that could have caused this disturbance, so astronomers believe that NGC 5238 swallowed a smaller satellite galaxy. Astronomers are looking for signs of the swallowed galaxy by closely studying the stellar population of NGC 5238, a task made possible by Hubble’s superior resolution. A telltale sign of the smaller galaxy would be groups of stars that have properties that differ from most of the other stars in NGC 5238, indicating that they originally formed in a separate galaxy. Another signal would be a burst of star formation that occurred suddenly around the same time the two galaxies merged. The Hubble data used to create this image will help astronomers determine the history of NGC 5238.

Despite their small size and unremarkable appearance, dwarf galaxies like NGC 5238 often contribute to our understanding of galaxy formation and evolution. One of the leading theories of galaxy evolution is that galaxies formed from the bottom up in a hierarchical fashion, with star clusters and small galaxies forming first from gas and dark matter. Over time, gravity gradually pulled these smaller objects together to form galaxy clusters and superclusters, explaining the shape of the largest structures we see in the Universe today. The merger of an irregular dwarf galaxy like NGC 5238 with a smaller companion is exactly the kind of event that could have started the process of galaxy assembly in the early Universe. Hubble’s observations of tiny NGC 5238 could help test some of our most fundamental ideas about how the Universe evolves.