How many galaxies are out there?

This is actually a hotly debated question among astronomers, and if you go back a hundred years, no one even knew that there was more than one galaxy--ours. Recent estimates put the number of galaxies in the universe at 200 to 400 billion. I've seen estimates of 500 billion. I personally believe that there is many times that number.

How do astronomers estimate the number of galaxies? Recently, they take long exposure photos of a small area of space through the Hubble telescope and count the number of galaxies they can see and then estimate the ones they can't see. This doesn't sound very accurate. Basically, they're using an estimate, not actual date.

Have you seen the map of the universe that shows all of the known galaxies? It looks like a sponge. There are uncountable super clusters of galaxies arranged in strings called filaments that twist and turn all over the place. If you thought that we are insignificant in our little corner of the Milky Way, this map makes us appear nearly nonexistent.

The other problem with determining the number of galaxies is the fact that red shift, the term used for the expansion of the universe, is indicating that galaxies at the edge of the observable universe are moving away near the speed of light. In other words, we can't see what's beyond this edge. There may not be an edge and the universe goes on forever. We just don't know. All we know now is that the radius of the visible universe is 14.0 billion parsecs (45.7 billion light years). That's really huge, and it's probably even larger than that. An estimate of that is around 2% more, but it's probably even more than this. Remember that the universe has been expanding since the big bang, which was 13.798 billion years. That means the universe is much bigger than if it were static (not expanding).

Another problem is that the universe has voids, large multi-light year bubbles where there appears to be no galaxies. Then, there are large lumps of galaxy clusters at nodes in the filaments of galaxies. This makes estimating the number of galaxies difficult.

Estimates of the number of galaxies are based on several other schemes. The number of stars is estimated at a maximum of ten to the twenty-fourth. This was obtained by multiplying the average number of stars in galaxies by the number of galaxies. Again, this is an estimate. Another way is to take the number of galaxies seen in a small section of the sky by the Hubble telescope and then multiplying by the rest of the sky. This could result in errors.

Some have tried to estimate the number of galaxies from the total mass of matter in the universe, but as we have seen, this doesn't take into account dark matter. Another idea is to try to estimate the number by doing a calculation based on a given horizon, such as our local group of galaxies, and then figure out what would happen if the universe expanded for nearly 14 billion years, the assumed age of the universe. This doesn't account for variations (lumpiness) in the universe. Some parts of the universe have more concentrated galaxies than others.
I think the main reason that it's difficult to estimate the number of galaxies in the universe is the fact that what we're looking at billions of light years away is what existed that many billions of years ago. In other words, it's what existed in the past, not what's in the present. We don't really know how many new galaxies are out there because the light from them hasn't gotten back to us.

Thanks for reading.