help

The Eventual Collision of the Andromeda and Milky Way Galaxies

-- | October 24, 2015

Question: If I understand the various articles I’ve read and programs I’ve seen on TV and the internet. It has been determined that the Andromeda and Milky Way galaxies are on a collision course and are destined to “collide” in about 4 billion years. My question is this. If the collision will happen, how can it? Given the observations thus far that all of the galaxies are receding from each other due to the expansion of space-time itself. — Guy

Answer: You are right in that on the large scale all galaxies are expanding away from each other. On smaller scales, though, there are what are called “peculiar motions” where galaxies can have motions relative to each other that are due to local gravitational attraction. The Andromeda and Milky Way galaxies have peculiar motions whereby they are moving toward each other, which results in the prediction that they will eventually collide.

Jeff Mangum

The National Radio Astronomy Observatory is a facility of the U.S. National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
	Founded in 1956, the NRAO provides state-of-the-art radio telescope facilities for use by the international scientific community. NRAO telescopes are open to all astronomers regardless of institutional or national affiliation. Observing time on NRAO telescopes is available on a competitive basis to qualified scientists after evaluation of research proposals on the basis of scientific merit, the capability of the instruments to do the work, and the availability of the telescope during the requested time. NRAO also provides both formal and informal programs in education and public outreach for teachers, students, the general public, and the media.
	The U.S. National Science Foundation (NSF) is an independent federal agency created by Congress in 1950 "to promote the progress of science; to advance the national health, prosperity, and welfare; to secure the national defense..."
	AUI collaborates with the scientific community and research sponsors to plan, build, and operate cutting-edge facilities. We cultivate excellence, deliver value, enhance education, and engage the public.