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As you probably know, galaxies like our Milky Way are made up of billions of stars. But how did we get from the first particles of hydrogen and helium left over from the Big Bang to the beautiful spiral galaxy structures we see today? What was the process of galaxy formation?
Shortly after the Big Bang, the Universe was entirely hydrogen and helium with a few other trace elements like lithium. Thanks to tiny fluctuations in density of this material, it started to clump together into vast clouds of gas with increasing density. Astronomers think that the process of galaxy formation was really led by dark matter, which outnumbers regular matter. This invisible material was also clumped together, and it attracted regular mass with its gravity, channeling material together into larger and larger collections. And so, the first proto-galaxies were formed.
Within these proto-galaxies, clumps of material gathered together, and eventually created star forming regions, and within these regions the first stars began to form. These stars lived short violent lives, and seeded the next generations of stars with the material created in their powerful supernovae. These first proto-galaxies were gravitationally attracted to one other, and merged together into larger and larger structures, eventually becoming the large spiral galaxies we know today.
But the process of galaxy formation is still going on today. Our Milky Way is expected to collide with the Andromeda Galaxy in the next few billion years, and created an even larger elliptical galaxy. We can see examples of these largest galaxies elsewhere in the Universe.
We have written many articles about galaxies for Universe Today. Here’s an article about new theories in galaxy formation.
We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.