Some Ancient Stars In Milky Way Were Born Elsewhere

Our Milky Way galaxy snatched up many of its most ancientstars from smaller galaxies that shredded each other in violent collisions, anew study suggests.

Using new supercomputer simulations, researchers found that someancient Milky Way stars did not form natively with the rest of the galaxy about10 billion years ago. Instead, they are actually the leftovers from other galaxiesthat collided about 5 billion years ago.

These stars make up some of the residents in the Milky Way's stellar halo,which extends above and below the spiral galaxy's main disk, researchers said.

"Effectively we became galactic archaeologists, huntingout the likely sites where ancient stars could be scattered around thegalaxy," said researcher and post graduate student Andrew Cooper of theInstitute of Computational Cosmology at Durham University in the UnitedKingdom.

"Like ancient rock strata that reveal thehistory of Earth, the stellar halo preserves a record of a dramatic primevalperiod in the life of the Milky Way which ended long before the sun was born," he added.

The new simulations began about 13 billionyears ago, just after the universe began, and then used universal laws ofphysics to chart how the gravitational attraction of the galaxies' dark matterhalos accumulated stars over time.

Dark matter halos are regions of invisiblematter around a galaxy which astronomers only infer exist because of theirgravitational effects on visible matter.

"The simulations are a blueprint for galaxyformation," said researcher Carlos Frenk, director of the Institute ofComputational Cosmology at Durham.?

Frenk said the simulations reveal clues intothe "early, violent history" of the Milky Way galaxy.

Researchers credited the unusually highresolution of the new simulation for its results. Capable of zooming in on thefine details of galaxy unraveling, the simulations showed streams of starsbeing pulled from clusters due to the gravity of hidden dark matter.

Most surprising was the similarity betweenthe simulated results and real observations, said Cooper.

"This shows that the cold dark mattermodel gives a convincing match to the real universe not just on very largescales, but also for individual Milky Way-like galaxies," he ?

The cold dark matter model is the current"standard model" of cosmology, which depicts galaxy formation in theuniverse as a process primarily arising from the clumping of dark matter.

The research is detailed in the journalMonthly Notices of the Royal Astronomical Society.


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