Oldest Stars of the Milky Way Migrated Via Violent Galactic Collisions


Recent research shows that many of the Milky Way's ancient stars are remnants of other smaller galaxies ripped asunder by violent galactic collisions around five billion years ago, according to researchers at Durham University's Institute for Computational Cosmology and their collaborators at the Max Planck Institute for Astrophysics, in Germany, and Groningen University, in Holland. The research is part of the Aquarius Project, which uses the largest supercomputer simulations to study the formation of galaxies like the Milky Way.

Their joint computer simulations revealed that the ancient stars, found in a stellar halo of debris surrounding the Milky Way, had been torn from smaller galaxies by the gravity generated by colliding galaxies.

Cosmologists predict that the early Universe was full of small galaxies which led short and violent lives, colliding with each other, leaving behind debris which eventually settled into more familiar looking galaxies like the Milky Way.

Andrew Cooper, from Durham University's Institute for Computational Cosmology, said: "Effectively we became galactic archaeologists, hunting out the likely sites where ancient stars could be scattered around the galaxy. "Our simulations show how different relics in the galaxy today, like these ancient stars, are related to events in the distant past. Like ancient rock strata that reveal the history of Earth, the stellar halo preserves a record of a dramatic primeval period in the life of the Milky Way which ended long before the Sun was born."

The computer simulations started from the Big Bang, around 13 billion years ago, and used the universal laws of physics to simulate the evolution of dark matter and the stars. These simulations are the most realistic to date, capable of zooming into the very fine detail of the stellar halo structure, including star "streams" — which are stars being pulled from the smaller galaxies by the gravity of the dark matter.

One in one hundred stars in the Milky Way belong to the stellar halo, which is much larger than the galaxy's familiar spiral disk. These stars are almost as old as the Universe.

Professor Carlos Frenk, Director of Durham University's Institute for Computational Cosmology, said: "The simulations are a blueprint for galaxy formation. "They show that vital clues to the early, violent history of the Milky Way lie on our galactic doorstep. Our data will help observers decode the trials and tribulations of our galaxy in a similar way to how archaeologists work out how ancient Romans lived from the artefacts they left behind."

Casey Kazan via EurekAlert!

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