Astronomers discover how galaxies form through mergers

Astronomers in the UK announce today that have established how galaxies like our own Milky Way formed over 10 billion years of cosmic time through an abundance of separate galaxies colliding together.

Galaxies are the largest single objects in the universe, and the origin of their formation is a very old question without any obvious answers. A major study submitted this week to the American Astronomical Society’s Astrophysical Journal has provided a solution to this problem.

Astronomers led by Professor of Extragalactic Astronomy, Christopher Conselice at The University of Manchester, have now established that this effect of merging is one of the dominant processes whereby galaxies come to be.

These researchers have concluded this decades-long study of galaxies and how they formed over the past 10 billion years revealing that these galaxy mergers are one of the most important methods for forming galaxies. The average massive galaxy over the past 10 billion years will undergo around 3 mergers with other galaxies, which will more than doubles their mass. This study has thus shown that mergers are a very effective way for galaxies to form.

“This also suggests that our own Milky Way galaxy has likely undergone at least one of these significant mergers during its history, which radically changed its shape and formation history,” Said Professor Conselice. “Mergers, such as the ones in this study, trigger star formation, which may be the origin event for how stars including our own Sun formed, as well as feed the matter that grows central black holes.”

Galaxies in the nearby universe come in all shapes and sizes. Some of them, including our own, are very massive with over a trillion stars and a spiral pattern. Others are enormous collections of stars with a spheroidal or ellipsoidal structure with no particular patterns. The history of these enormous systems is largely unknown. 

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