How do bars form in spiral galaxies? (Intermediate)

Where can I find reliable information about barred spiral galaxies, ie; how they are formed, theories of their evolution, etc.?

Despite their simplistic appearance, the formation of spiral galaxies is an extremely complex problem that is not yet fully solved. One of the oldest ideas is that the spiral arms are simply being wrapped around the centre due to differential rotation, however this idea is not viable as during the age of the Universe spiral galaxies will have completed many tens of revolutions and so would all have very tightly wound arms, which is not the case. Another idea is that when star formation is triggered at a particular point in a rotating galaxy, as the star formation activity spreads out from that source it will naturally form a spiral pattern. This could potentially explain the more flocculent spirals, but not the beautiful grand design spirals. Today the most widely agreed upon explanation is that the arms we see are areas that are currently being compressed (triggering star formation) by a density wave passing through the galaxy, either caused by interaction with neighbouring galaxies or by the presence of a bar in the centre of the galaxy. The latest simulations, such as the Illustris project, have just begun to create realistic looking spiral galaxies for the first time.

This page was last updated on September 16, 2015

About the Author

Mike Jones

Mike is a fourth year astronomy graduate student at Cornell, where he works with Professors Martha Haynes and Riccardo Giovanelli on the ALFALFA survey, a blind survey of gas-rich galaxies in the local Universe carried out with the 305m Arecibo telescope in Puerto Rico.


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