‘Inside-out’ galaxy growth observed in the early universe
A new study published in the journal Nature reveals a fascinating discovery about the growth of galaxies in the early universe. Astronomers have observed an “inside-out” pattern of growth in galaxies, where the central bulge forms first, followed by the outer disk. This finding challenges existing theories and provides valuable insights into galaxy formation.
The study was conducted by an international team of scientists led by researchers at the University of Tokyo. They used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to observe a galaxy named A2744_YD4, located approximately 12.4 billion light-years away. This galaxy existed during a time when the universe was only 1.4 billion years old, making it a crucial window into the early stages of galaxy formation.
By analyzing the distribution of dust and gas in A2744_YD4, the researchers found a distinctive pattern of growth. The galaxy’s central bulge, which is a dense cluster of stars, had already formed and was emitting a bright infrared glow. However, the outer disk, which surrounds the bulge, was still relatively small and faint. This “inside-out” pattern of growth suggests that the bulge formed first, followed by the disk gradually expanding outward.
This observation challenges traditional models of galaxy formation, which typically assume that the disk forms first, followed by the bulge. The study’s lead author, Takuya Hashimoto, explained: “Our observations of A2744_YD4 indicate that a different scenario, ‘inside-out growth’, occurred in the early universe. This challenges the conventional view of galaxy formation, where disks are considered to form first. This also means the origin and formation of the bulge is even more mysterious than we thought.”
The “inside-out” growth observed in A2744_YD4 is thought to be driven by the rapid influx of gas and dust into the galaxy’s central region. As the gas falls into the bulge, it heats up and triggers the formation of stars. The bulge then grows as more stars form within it. However, as more gas falls into the center, the galaxy begins to rotate. This rotation gradually pushes some of the gas outward, forming the disk.
This new finding sheds light on the complex and fascinating process of galaxy formation. It highlights the diversity of galaxy growth strategies in the early universe, and it poses new challenges for our understanding of how galaxies evolve. Further observations of early galaxies with ALMA and other powerful telescopes will help to clarify the different growth patterns and provide a more complete picture of how these structures formed.
