Previously, it was unknown whether the far-future encounter will be a miss, glancing blow, or head-on smashup. This depends on M31's tangential motion. Until now, astronomers have not been able to measure M31's sideways motion in the sky, despite attempts dating back more than a century. The Hubble Space Telescope team, led by van der Marel, conducted extraordinarily precise observations of the sideways motion of M31 that remove any doubt that it is destined to collide and merge with the Milky Way.
"This was accomplished by repeatedly observing select regions of the galaxy over a five- to seven-year period," said Jay Anderson of STScI.
"In the 'worst-case-scenario' simulation, M31 slams into the Milky Way head-on and the stars are all scattered into different orbits," said team member Gurtina Besla of Columbia University in New York, N.Y. "The stellar populations of both galaxies are jostled, and the Milky Way loses its flattened pancake shape with most of the stars on nearly circular orbits. The galaxies' cores merge, and the stars settle into randomized orbits to create an elliptical-shaped galaxy."
The space shuttle servicing missions to Hubble upgraded it with ever more-powerful cameras, which have given astronomers a long-enough time baseline to make the critical measurements needed to nail down M31's motion. The Hubble observations and the consequences of the merger are reported in three papers that will appear in an upcoming issue of the Astrophysical Journal.
The science team that did the investigation is led by Principal Investigator R.P. van der Marel (Space Telescope Science Institute [STScI], Baltimore, Md.), and further consists of S.T. Sohn and J. Anderson (STScI), G. Besla (Columbia University, New York, N.Y.), M. Fardal (University of Massachusetts, Amherst, Mass.), R.L. Beaton (University of Virginia, Charlottesville, Va.), Thomas M. Brown (STScI), P. Guhathakurta (UCO/Lick Observatory, University of California, Santa Cruz, Calif.), and T.J. Cox (Carnegie Observatories, Pasadena, Calif).
For images, video, and more information about M31's collision with the Milky Way, visit:http://hubblesite.org/news/2012/20
Ray Villard | Newswise Science News
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