Why don't galaxies that are not rotating collapse?

25 February 2011

Question

I have a question for the Naked Astronomers - Why don't galaxies that are not rotating all collapse?

I believe that Spiral Galaxies rotate but elliptical galaxies do not.

I understand the universe can / is expanding because of the energy of the big band, but would expect all non-rotating galaxies to aggregate and eventually form massive black holes. Without centrifugal force what stops this from happening? Dark energy, is the gravity too weak or will they given enough time?

Hope you can straighten this our for me, it has puzzled me since you explained on the shows that elliptical galaxies where relatively static, it suprised me.

Love your programme, I never miss a podcast - keep up the good work.

Colin Strand
Ashford, Kent

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