Our closest neighbor stars
Our sun and the solar system, including the Oort cloud, are roughly 1 to 2 light years in diameter. This is a much greater distance than just to Neptune, which is a mere four and a half hours away at the speed of light. This solar system is part of the Milky Way Galaxy, roughly 100,000 light years in diameter. So the orbit of Neptune is a tiny speck in size compared to the entire Galaxy.
In the Milky Way, we have many neighbors. Alpha Centauri is best known as our closest neighbor star, and speculations of planets and life within reach have been the subject of science fiction. Alpha Centauri is three stars drawing each other together with gravitational force while maintaining their distance with the centrigfugal force that could make us fall off a merry-go-round.
The Alpha Centauri group rotates between 4.25 and 4.35 light years from our sun, well beyond the Oort cloud. Some science fiction stories tell of planets with multiple suns, probably inspired by our knowledge of Alpha Centauri. We have known for hundreds of years that Alpha Centauri was two stars, and in 1915 a Scottish astronomer proposed that a third star was part of the group.
While light from the sun takes around eight minutes to reach Earth, the size of the rotation of the Centauri stars is ten percent of a year or around 40 days. This would make it unlikely that a planet could exist gravitationally in a zone heated by the stars of Alpha Centauri. Scientists believe that more stars exist in binary or tertiary orbits that singular masses such as the sun. If this is true, this could be an important factor to consider in the Drake equation.
The Drake equation states that the probabilty of live elsewhere in the universe is dependent on the probability of a number of factors. But scientific research since the Drake equation was proposed has produced a number of factors making it less likely that life as we know it can evolve. Certainly the Star Trek notion of hopping from one warm, fertile planet to another is less likely that portrayed. We need to find planets that are between five and 15 light ‘minutes’ from a singular star, warmed by that star but not burned up. But in a universe with billions of galaxies, you would think life somewhere had four billion years to evolve.
The universe is so vast, more and more study is done on the possibility of life evolving elsewhere in the Milky Way Galaxy. Here too, we have learned that we perhaps have good fortune to be near the edge of the galaxy and not nearer the middle. Peering into the galaxy we find higher rates of radiation, black holes and nuetron stars, all which can wipe out DNA life forms in an instant. But to look at our galaxy from 360 degrees we would first need to travel around the edge of the Milky Way, a trip of 300,000 light years.
A better idea would be to travel a ways in and out of our local arm of the Milky Way. A spiral galaxy, the Milky Way seems to have two arms like a lawn sprinkler radiating out from the center. While it has been more than 40 centuries since mankind built the pyramids, in another 40 centuries we could explore perhaps that closest neighbors in our spiral arm.