The observable universe is the section of the Universe where light emitted since the Big Bang has had enough time to reach Earth. It's our bubble of visibility in the universe.
There's likely one hundred billion galaxies in the observable universe.
Wikipedia, Visible universe
A reasonable option is to assume 100 billion average galaxies and 100 billion stars per average galaxy. This results in 10^22stars.
Paraphrased from 'AFP in Paris', Universe has 2 trillion galaxies, astronomers say.
Apparently this may have been recently updated to two trillion (20 times as many).
If you were to chop it up, a piece would look like this:
- Wikipedia, Void (astronomy)
- Matter distribution in a cubic section of the Universe. The blue fiber structures represent the matter (primarily dark matter) and the empty regions in between represent the cosmic voids.