How Many Galaxies Have We Discovered?

Hubble Ultra Deep Field. Credit: NASA

Astronomers think that there are hundreds of billions galaxies in the universe, however the exact number is not known. But astronomers should know how many galaxies we've actually seen and discovered, right? Well, not necessarily. “We don’t know,” says Ed Churchwell, professor of astronomy at the University of Wisconsin-Madison. “We know it’s a very large number.” In just one image for example, the Hubble Ultra Deep Field, above, there are about 10,000 galaxies visible.
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