Is there an estimation of how many stars there are in this known universe?
Yes, but it is very rough so far as I know.
There are estimated to be about (and I do mean that) 100 billion galaxies, each with an average of several hundred billion stars in it.
This gives us
Like I said, pretty vague, but safe to say it is a very large number (incidentally it is about a mole of stars, of no consequence, just makes you think ...)