The Milky Way, is the galaxy in which we live and has an estimated 150-200 billion stars in it. Not too many decades ago, we thought The Milky Way was the whole universe. We now know with the launch of the Hubble Telescope in the 1990's, that the Milky Way is only one very small part of the billions or possibly even trillions of other galaxies we see.
In 2016 NASA updated the number of galaxies in the universe by ten times the once thought billions to trillions of galaxies. A new generation telescope named the James Webb Telescope will be launched in late 2018, and once in service will no doubt thrust the estimate even higher.
The Milky Way resides in a super cluster of galaxies named Laniakea Super Cluster. Laniakea (Lan-e-i-k-ah) in Hawaiian means Immeasurable Heaven. with hundreds of thousands of galaxies within it.
Consider the known universe with over 150 billion Milky Way sized galaxies with an estimated 1,500,000,000,000,000,000,000 or 1.5 sextillion plus stars. This estimate, by the way, is a very fluid number since any estimate you see is only at best a guesstimate. Yes, a sextillion is a real name for a family of numbers and is 1000 times a quintillion and a quintillion is 1000 times a quadrillion which is 1000 times a trillion, got it? Its one of those numbers that the mind cannot comprehend.
When you consider that the current matter we are able to detect (see, detect wit x-rays, gamma rays etc.) is only about 5% of the universe, and we cannot see the rest because it is composed of black matter or dark energy, our understanding of our world is quite limited.
We cannot detect the dark stuff but mathematically we think it has to be there since, without it, the universe's expansion would not be accelerating. Also, we see galaxies in which stars on the outer perimeter travel at the same speed as stars surrounding the interior, this demands an additional force or mass that we cannot detect.
We believe the diameter of the universe is somewhere in the 93 billion light year range or 546,710,994,417,600 miles. however it is suspected it could be as much as 160 billion light years but there is no way to measure or know for sure.
In 2012 the Hubble Telescope was focused on a single point in space, once thought to be void of anything, however, after zooming in on the location, it revealed a much larger estimate of galaxies and with this new information, we think the universe could contain as many as 100 Octillion stars or 100,000,000,000,000,000,000,000,000,000 stars. Do not even try to wrap your mind around that number.
The Known Universe video below will give a visual picture of just how massive the universe is. While we currently estimate the age of the universe to be 13.8 billion years old, this is dependent on assuming the speed of light always remained constant and photons traveling from the sources also remained constant. Just when we think we have seen as far as we can, we find more.
Below are images of our current understanding of some of the clusters and super clusters of galaxies, please note these are galaxies with billions of stars and not single stars. These images are what we think they may look like.