NoelC wrote:It doesn't seem to me that stars being a few light years apart is enough to be a problem for planets. How is it, for example, that our own almost-star Jupiter has a nice set of satellites in perfectly good orbits? It's only a few light-hours from the nearest star.
I've seen simulations that suggest that a single star passing within a few tenths of a light year of the Sun could destabilize the Solar System. The stellar density in the bulge of the Milky Way is between 1000 and 2000 stars per cubic light year. It is doubtful that stable planetary systems could exist in such a region. The situation in that environment is very different than what you have with Jupiter's system, which while chaotic, is essentially metastable. Unstable orbits have already been weeded out. But a planetary system in a dense galactic core sees a non-repeating set of gravitational perturbations. Essentially, every close encounter is a new event, introducing its own unique set of instabilities.
Are you proposing that the planets wouldn't form to begin with?
I'd expect planets to form in most star systems, including those in dense regions. Planetary system formation seems to be very quick- a few million years. Chaotic instabilities probably manifest over tens or hundreds of millions of years, so stars will tend to have all but very closely orbiting planets cleared out. At the least, planets will get shifted into different orbits, meaning that even where planets exist, they are almost certainly hostile to the development of life (or life requiring significant evolutionary time).
The Antennae
