How many planetary systems exist in our galaxy?
For many years scientists have studied our own solar system and modern technology allows them to look deeper and deeper into space. Knowing the Sun is only one of a few billion stars in the Milky Way galaxy, I can imagine scientists also started studying other planetary systems… at least enough to know how many planetary systems (like our solar system) reside in our galaxy.
Is there any information available that would be able to (at least "indicate") how many planetary systems reside in our galaxy?
I think this should be changed to 'How many star systems are in our galaxy?' There is only one solar system - the system surrounding the sun. That's what solar means.
I've edited the question to use "planetary system" instead of "star system", as that seems to be the intent. See Wikipedia for the difference: Star system vs. Planetary system. This doesn't affect the answers in any way. It just makes the question more accurate.
A good, but hard question to answer - as you stated, only an indication could be provided. But, there is some information available from the number of exoplanetary systems found 'locally', according to the NASA web page How many solar systems are in our galaxy?:
So far, astronomers have found more than 500 solar systems and are discovering new ones every year. Given how many they have found in our own neighborhood of the Milky Way galaxy, scientists estimate that there may be tens of billions of solar systems in our galaxy, perhaps even as many as 100 billion.
Another estimate from the article 160 Billion Alien Planets May Exist in Our Milky Way Galaxy (Hall, 2012), particularly with their quote from a scientist:
"This statistical study tells us that planets around stars are the rule, rather than the exception," said study lead author Arnaud Cassan of the Paris Institute of Astrophysics. "From now on, we should see our galaxy populated not only with billions of bright stars, but imagine them surrounded by as many hidden extrasolar worlds."
An important caveat from the NASA site is that exoplanetary observations are still in its infancy - so over time, this estimate is likely to improve.