Our neighbor has been getting beat up.
The Andromeda galaxy has a much more violent existence than the Milky Way, according to a study by The University of California - Santa Cruz of stellar population movements. Andromeda, according to findings presented on Thursday at the American Astronomical Society, has had some violent run-ins with smaller galaxies.
Andromeda, also known as M31, is the closest spiral galaxy to the Milky Way and the largest in the neighborhood.
"In the Andromeda galaxy we have the unique combination of a global yet detailed view of a galaxy similar to our own," said Puragra Guhathakurta, a professor of astronomy and astrophysics at the UCSC. "We have lots of detail in our own Milky Way, but not the global, external perspective,"
Data from two large surveys were merged by Guhathakurta and another UCSC graduate student, Claire Dorman. The data from the W. M. Keck Observatory in Hawaii and the Hubble Space Telescope were main highlights of the study.
"The high resolution of the Hubble images allows us to separate stars from one another in the crowded disk of Andromeda, and the wide wavelength coverage allows us to subdivide the stars into sub-groups according to their age," said Dorman.
The astronomers found that young stars follow a rotational motion around the heart of the galaxy while older stars were more disordered with a wide range of speeds.
"If you could look at the disk edge on, the stars in the well-ordered, coherent population would lie in a very thin plane, whereas the stars in the disordered population would form a much puffier layer," Dorman said.
"Our findings should motivate theorists to carry out more detailed computer simulations of these scenarios," she added.
The varying ages as determined by the study suggest a few violent meetings between Andromeda and smaller galaxies. "Even the most well ordered Andromeda stars are not as well ordered as the stars in the Milky Way's disk," Dorman said.
The "Lambda Cold Dark Matter" archetype of universal formation states that large galaxies (like Andromeda and the Milky Way) have grown by swallowing smaller satellite galaxies. The researchers at UCSC think that while the Milky Way is too organized for that to have happened, Andromeda looks just the type.
"In this context, the motion of the stars in Andromeda's disk is more normal, and the Milky Way may simply be an outlier with an unusually quiescent accretion history," Guhathakurta said.
