originally posted by: jonnywhite
originally posted by: Ross 54
For stars within ~ 16 light years I used wikipedia:
For the rest, I used the following rendering of data from the Hipparcos Catalog:
One interesting thing to note is as one goes further out from SOL there're more and more stellar neighbors because the "bubble" expands its surface
area exponentially, thus probabilistically encountering more neighbors as it grows. My math is not good, but thanks to google I can (maybe) get this
across. According to google, the surface area of a sphere is 4πr^2. This means the area for a sphere with a 2 light-year diameter is 12.566. If you
double the diameter of the sphere the surface area does not double as well, it instead grows exponentially to reach 50.265 ly. Another doubling so
that its diameter is 8 ly results with a surface area of 201.062 ly. If you examine the list of the 500 closest stars, it does seem to match the
expectation of an exponential growth in the number of neihbors:
Stars within 8 ly: 4
Stars within 16 ly: 35 (4 + 31)
Stars within 32 ly: 132 (4 + 31 + 97)
Good work and not too far off either for the estimates closer to home but your methodology breaks down as you get further out. Don't let that
discourage you though, I love when anyone on ATS uses math to extrapolate stuff like this given a data set.
I wonder what the average density of stars is per volume of given (nearby) interstellar space?
Number = density * volume
In our neck of the woods the average density is around 1 star for every 280 cubic light years.
So this gives us ROUGHLY:
Stars within 8 light years = 33
Stars within 16 light years = 117
Stars within 32 light years = 458
Stars within 64 light years = 3,803
Stars within 128 light years = 30,426
Stars within 256 light years = 243,00
Stars within 512 light years = 1,947,273
Stars within 1,024 light years = 15,578,187
These estimates vary from our catalogs which means that in some cases as much as half the stars remain undiscovered as they are small, dim, low mass M
stars aka red dwarfs.
Roughly 1/4 to 1/2 if those stars in each distance category are thought to host an Earthlike planet in the habitable zone of its star.
Assuming that, then the probability of the nearest Earthlike planet being around 12 light years away is around 99.9%
So it's quite likely we have quite a few neighboring earths within 32 light years (about 100 as a very conservative number). Other estimates say
between 160-190 earths within 32 light years. With an average age of around 6 billion years (or roughly 1.5 billion years older than our Earth) which
raises a fascinating possibility: That we'd be babies perhaps surrounded by a room full of nearby adolescent and young adult civilizations.
I imagine they cluster, so any averaging is loose. I also know there'r galaxies which're denser than others.
The density estimate varies across the galaxy of course, the density decreases rapidly in the direction out of the galactic plane whether above it or
below it. It also increases a lot as you move along the plane starting roughly around 18,000 light years in the direction of the center of the galaxy
when the density is the highest (around 1,000 stars per cubic light year) . It also is substantially higher in globular clusters within the galaxy. It
also falls off slightly between spiral arms.
BTW: There are some other nearby stars in the star field this latest discovery was made in.
(pc) = parsec - 1 parsec = 3.26 light years
edit on 19-12-2014 by JadeStar because: (no reason given)