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Galactic Empire

March 27, 2018

Our home galaxy, the Milky Way, is a giant — far bigger, brighter, and heavier than most other galaxies. Because of that, it dominates the space around it — dozens of smaller galaxies orbit it like moons orbiting a giant planet, held by the Milky Way’s gravity.

Most of these satellite galaxies have been discovered only recently. Just 20 years ago, astronomers knew of only about a dozen galaxies orbiting our own. Today, the number stands at around 50. And as astronomers deploy bigger and bigger telescopes, they’re almost certain to see more — the final number could well top a hundred.

Although these are our closest neighbors, most of them are faint, so they’re hard to see. Only two of the Milky Way’s galactic satellites — the Large and Small Magellanic Clouds — are visible to the unaided eye.

But the many little puffballs that orbit the Milky Way reveal a basic fact about the universe: It has a lot more small galaxies than big ones. And our galaxy is definitely a big one — probably in the top one percent of all the galaxies in the universe.

But while the Milky Way is special, it’s not unique. Other giant galaxies also host many smaller ones. The Andromeda galaxy, for example — the closest giant galaxy to the Milky Way — boasts dozens of satellites.

These galaxies suggest that most of the small galaxies in the modern-day universe are dominated by giants — like the Milky Way.

We’ll talk about another group of galaxies tomorrow.


Script by Ken Croswell

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