The first galaxies
A few hundred million years after the Big Bang, the first stars entered the cosmic stage. So how did the first galaxies form? New simulations now indicate that small building blocks of a few thousand solar masses collided with each other and became faint dwarf galaxies. Some of these objects survived to this day and can even be observed as part of our Milky Way system.
Over the past 20 years, astronomers have made tremendous strides in understanding how the Universe was able to transform from a very simple initial state into the rich and diverse cosmos we observe today. But with every step forward, intriguing new questions emerged. Some of the central aspects deal with how the early stages of structure formation in the universe occurred, how the first stars and first galaxies formed and what is observable today to learn new things about these important processes. Fortunately, researchers don't have to look beyond their galactic backyard to address these fundamental questions. The oldest stars in our home galaxy, around 13 billion years old, provide clear clues. They are survivors that were probably formed in the first small protogalaxies a few hundred million years after the Big Bang, at a time when the loose gas in the universe was first arranged into regular structures by gravity. However, many of these dwarf galaxies were soon swallowed up by their slightly more massive and thus faster growing neighboring galaxies.
