Expert: Courtney Seligman - 6/7/2010

Question
How long does it take for a galaxy to be formed? also, what are the steps to forming a solar system? How long does this take? Help! I have an astronomy project due very soon.

Answer
For solar systems, refer to http://cseligman.com/text/ssevolve/ssorigin.htm (The Origin of the Solar System). Among other things, you'll find a graph showing the rate of growth of the Jovian and Terrestrial planets, indicating that Jovian planets took (in our case) a few million years to form, and Terrestrials a couple of tens of millions of years. These times refer to the initial formation of the planets, and do not include the few hundred million years of bombardment following their initial buildup; but I would view that as part of the evolution of planetary surfaces, not as part of their original formation.

For galaxies, there is no single answer. The first galaxies appear to have formed in just a few hundred million years, very early in the history of the Universe. But the present galaxies mostly represent much larger structures which have formed as a result of collisions and mergers of the original galaxies. So in some ways, galaxies are still "forming" in regions where such collisions are still going on(namely, rich clusters of galaxies). As a result, you could specify times ranging anywhere from a few hundred million years for galaxies which have not substantially altered since their initial formation, to a few billion years for galaxies which underwent substantial mergers early on but are no longer undergoing such mergers, to more than ten billion years for galaxies which are still merging and growing.