How many Galaxies?

How Many Galaxies Are There in the Universe? The Redder We Look, the More We See

Ethan Siegel is a theoretical astrophysicist living in Portland, Oregon, who specializes in cosmology. He has been writing about the Universe for everyone since 2008, and can’t wait for the launch of the James Webb Space Telescope. A different version of this post appeared on his blog, Starts With a Bang. 

“It is by going down into the abyss that we recover the treasures of life. Where you stumble, there lies your treasure.” –Joseph Campbell

One of the bravest things that was ever done with the Hubble Space Telescope was to find a patch of sky with absolutely nothing in it—no bright stars, no nebulae, and no known galaxies—and observe it. Not just for a few minutes, or an hour, or even for a day. But orbit-after-orbit, for a huge amount of time, staring off into the nothingness of empty space, recording image after image of pure darkness.

What would we find, out beyond the limits of what we could see? Something? Nothing? After a total of more than 11 days of observing this tiny area of the sky, this is what we found:

The Hubble Ultra Deep Field—the deepest view ever of the Universe, was the result. With all those orbits spent observing what appears to be a blank patch of sky, what we were really doing was probing the far-distant Universe, seeing beyond what any human eye—even one aided by a telescope—could ever hope to see. It took literally hundreds of thousands of seconds of observations across four separate color filters to produce these results./.../