|How many solar systems could be in a galaxy if
there a billions of stars in a galaxy?
|Question Date: 1999-05-27|
there are about 100 billion ( 100,000,000,000.)
stars in the MIlky Way galaxy which is only one of
about 3000,000,000,000. galaxies in the known
It is presently believed that
solar systems form around many stars. It is only
within the last few years that we have detected
EXTRA SOLAR planets...that is, planets around
but the models we have for
star formation seem to indicate that many stars
will develop a family of planets.
only 0.1% of stars in the MILKY WAY have planets,
that means that there are still ten million solar
systems in the MILKY WAY.
so the best
estimates we have for the number of solar systems
is : at least 1 million and maybe 100 billion.
this is a big range . it represents our
uncertainty regarding this issue. probably 100
years from now we will have a better answer to
this question. this is how Science works. 100
years ago we didnt even know that most stars in
the UNIVERSE are located in specific structures
(clumps) called Galaxies. and 100 years before
that we had no idea of what made stars burn
Science is a process of discovery; we
slowly lift the shroud of fog and finally see
clearly the way the universe has been
Our galaxy has approximately 2x10^11 stars, of
which many are binary (two or more stars in orbit
around each other). Binary stars can have planets
so long as the stars are very close compared to
the planets orbital radius, or very far, so let's
make a guess that only 1x10^11 stars are able to
have planets around them.
astronomers have detected 19 planets around 17
other stars, which is about 4% of the stars that
have been studied. However, only planets that are
the size of Jupiter or larger can be detected, so
there may be others. Four percent of 1x10^11 is
4x10^9 or four billion.
Many of the planets
that have been found are very massive and have
highly eccentric orbits, which implies that there
are no other planets around the star. These
planets would likely be inhospitable to
To determine this, it is necessary to know what
fraction of the stars in a galaxy have any sort of
a solar system. Multiplying this fraction by the
total number of stars would give a rough estimate
of the number of solar systems. The difficulty
with this is that even our most powerful
telescopes (like the Hubble space telescope) are
only barely able to see indications of planets
around other nearby stars and those planets need
to be very large ones like Jupiter or Saturn.
Large planets such as these suggest that there are
smaller planets like the Earth closer to the star
but we have no way of knowing if this is the case
with our current technology. If 10% of the stars
in the galaxy have some sort of solar system and
there are 300 billion solar masses worth of stars
in the Milky Way (assume that means 300 billion
stars), how many solar systems would there be? Of
course, if you're interested in solar systems that
might be suitable for life, this number drops
There are actually HUNDREDS of billions of stars
in our galaxy, and it seems likely that the vast
majority might have planets orbiting around them,
given the frequency with which we are currently
detecting planets around other stars. So there
could be literally hundreds of billions of solar
systems. How many of these planets would provided
suitable conditions for life to evolve is,
however, a completely open question.
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