Galaxy Fundamentals

Why do galaxies have different shapes?

Originally, when Edwin Hubble created his tuning fork diagram, he hypothesized that galaxies followed a sequence as they aged: all galaxies would be elliptical at first, and then flatten out over time as they spun. This idea was disproven, however.

Modern computer simulations and mathematical calculations now show that all galaxies form by the collection of smaller clumps of matter—subgalactic “clumps” that fall together into a single gravitational unit. If lots of little clumps collect, it usually becomes a spiral galaxy; but if there are some very large clumps that come together toward the end of the process, then it usually results in an elliptical galaxy. This model of galaxy shape-forming appears to be generally correct, but a number of details still need to be worked out to make a coherent theory.


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