Stealth Merger of Dwarf Galaxy

According to new study small newfound galaxy with an oddball shape may be the product of a close encounter with a neighboring galaxy in what scientists are calling a “stealth merger”. The cosmic discovery came as astronomers investigated an isolated dwarf galaxy known as NGC 4449, which is about 12.4 million light-years away and is a “starburst galaxy,” meaning it forms young stars at a furious pace. This galaxy has a distorted shape as well, a look that is wreathed in hydrogen gas abounding with rings, shells and a core spinning the opposite way of the galaxy. Researchers have suspected the galaxy’s hyperactivity and complexity might be due to it tangling with another galaxy. Now, two different teams of scientists have detected the most likely galactic interloper ,a previously unseen dwarf galaxy about 29,300 light-years from NGC 4449. Dubbed NGC 4449B, it is the largest dwarf galaxy known in the “local group” that includes the Milky Way and the Andromeda galaxy. One team detected a stream of stars has been spotted between the NGC 4449 and NGC 4449B galaxies, suggesting that they are in the process of merging. The researchers dubbed the interaction a “stealth merger” because the smaller galaxy NGC 4449B was nearly imperceptible, but has a profound effect on the shape of its partner. Astronomer Aaron Romanowsky of the University of California, Santa Cruz, and his colleagues detail their findings in a study to appear in Astrophysical Journal Letters. They used telescopes in California and Hawaii to photograph the two galaxies.