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Blue Sky Science: How many galaxies are in the universe?

Gus Powvens

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How many galaxies are in the universe?

Galaxies are clouds of stars that range in both size and composition. Some contain hundreds of millions of stars while the largest galaxies can contain trillions of stars. And while it’s not entirely clear, most galaxies seem to be associated with a massive black hole so it’s possible that’s one of their distinguishing features.

Counting the number of galaxies in the universe is tough, because we can’t see all of the galaxies in the universe. At a certain point, distant galaxies disappear from our field of view.

They sort of cross over the horizon, and we can’t see anything beyond.

But in the visible universe, how many galaxies are there? Researchers explore that question by looking at a small patch of sky, counting the galaxies present, and then supposing that circumstances are the same around the whole sky.

You count up all the galaxies you can see in the small patch of sky, and then multiply by how much bigger the entire sky is.

This was done a few years ago with an image taken with the Hubble Space Telescope called the Hubble Deep Field. This image revealed very distant galaxies, and the math estimated that there were around 120 billion galaxies.

Recently there’s been a study using new data from the Hubble telescope again, but this time trying to figure out how many galaxies are being missed when those calculations and estimations are made. When galaxies are nearby we can see more, including smaller, dimmer ones. But as they get farther away, those smaller, dimmer galaxies are harder to see and disappear from the count.

With this new research the number is now closer to two trillion galaxies in the visible universe, a factor of 10 more than we would have counted before.

About Blue Sky Science

Blue Sky Science is a collaboration of the Wisconsin State Journal and the Morgridge Institute for Research. The questions are primarily posed by visitors attending Discovery Building events.

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