What would the consequences be of a high number of solar systems being within close proximity to one another?
What would the consequences be of a high number of solar systems being within close proximity to one another? I'm mainly interested in the consequences for life on multiple planets. When I say 'close proximity' I mean the stars all being between 1000-100,000 AU apart from one another, and roughly all being G-category stars?
I'm trying to create a setting where the distances between other exo-planets is not as vast as our own relative position in the galaxy, due to the issues limiting light-speed space travel.
The effects I am taking note of are:
- Gravitational effects (how much the stars will be attracting one another, and how it will affect planetary orbits)
- Stars heating planets
- The amount of light being received by close stars
Would habitable planets be able to survive with such a dense amount of stars nearby? If so, what are other variables to consider that would change the planets features?
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1 answer
Your environment is quite similar to that in a globular cluster. At its densest, a globular cluster may see peak stellar number densities of $\sim1000$ stars per cubic parsec, which implies a mean separation of about 20,000 AU. This leads us to conclude that many, if not most, planets will be stripped away through encounters with other stars, leading to a large population of free-floating planets.
Your systems will experience the same problems. However, $N$-body simulations have revealed some characteristics of the planetary systems that will survive intact:
- Planets will likely have orbits close to their parent stars. For instance, planets around pulsars would likely have semi-major axes of $\sim0.1\text{-}1.0$ AU.
- Moreover, systems with large numbers of planets are quite unlikely, given that multi-planet systems are even more susceptible instabilities after experiencing these encounters.
With mean distances of a few tens of thousands of AU, light from other stars will not affect habitability, thanks to the inverse-square law. A star 20,000 AU away should contribute a bit more than one billionth the flux of the Sun, if the Sun was 1 AU away.
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