The Hubble Space Telescope of the National Aeronautics and Space Administration (NASA) has captured images of the NGC 5238 galaxy. The distorted shape of this dwarf galaxy suggests that it may have experienced a merger with another galaxy. This provides clues for understanding the formation and evolution of galaxies.
According to a report on NASA’s website on July 19th, NGC 5238 is an irregular galaxy located in Canes Venatici, approximately 14.5 million light-years away from Earth. Its unremarkable appearance makes it resemble a giant star cluster more than a typical galaxy. Despite its unassuming exterior, it possesses intricate structures, making it a subject of extensive research.
Irregular galaxies, like NGC 5238, lack distinct regular shapes and do not resemble spiral or elliptical galaxies. Some irregular galaxies may have once been spiral or elliptical galaxies but were distorted due to uneven external gravitational forces.
NASA stated that the Hubble Space Telescope can identify numerous stars within NGC 5238 and associated globular clusters—bright spots within and around the galaxy that are clusters of more stars.
Astronomers speculate that NGC 5238 may have had a close encounter with another galaxy around 1 billion years ago. The twisted shape of NGC 5238 provides evidence of this interaction.
During the interaction between these two galaxies, the gravitational forces distorted the distribution of stars within each galaxy. Since no nearby galaxy could cause this situation, astronomers believe that NGC 5238 may have absorbed a smaller satellite galaxy.
Astronomers searched for traces of the swallowed galaxy by examining the number of stars within NGC 5238. This task was made possible by the outstanding resolution of the Hubble Space Telescope.
A clear sign of a smaller galaxy is that the attributes of its stellar population differ from the majority of stars in NGC 5238, indicating that they were initially formed in a separate galaxy. Another indication is the sudden formation of a large number of stars around the time of the merger of these two galaxies.
Although dwarf galaxies like NGC 5238 are small in size and unassuming in appearance, they contribute to our understanding of galaxy formation and evolution.
A primary theory of galaxy evolution suggests that galaxies form in a hierarchical “bottom-up” manner—first forming star clusters and small galaxies from gas and dark matter. Over time, gravity gradually combines these smaller bodies into galaxy clusters and superclusters, shaping the largest structures we see in the universe today.
Irregular dwarf galaxies like NGC 5238 merging with smaller companion galaxies serve as events that possibly initiate the galaxy assembly process in the early universe. Observations of NGC 5238 by the Hubble Space Telescope could help examine some of the fundamental concepts of how the universe evolves.
The Hubble Space Telescope has also captured images of merging galaxies that resemble a “Great Pumpkin,” “Space Triangle,” “Antennae,” and “Mice.”
Although galaxy mergers are highly intense, their occurrence rate is slow like a snail—spanning billions of years. The Hubble Space Telescope has only captured snapshots of some of these merger processes.
Such galaxy mergers allow us to envision the future collision between the Milky Way and the neighboring Andromeda galaxy. The Andromeda galaxy is approximately 2.5 million light-years away from Earth and is expected to collide with the Milky Way in around 4 billion years.