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This is a real photograph of the Universe.

The Universe is the name astronomers give to the vast space which contains everything we know, from great clusters of galaxies to the tiniest of particles. Professional astronomers have gathered clues about its evolution by capturing the light from galaxies many billions of light-years away. [1]

The Big Bang[edit | edit source]

The Universe is thought to have been born 13.7 billion years ago in a searing hot maelstrom known as the Big Bang. One strong piece of evidence for this energetic beginning comes in the form of a ubiquitous source of microwave radiation appearing across the whole sky, known as the Cosmic Microwave Background (CMB). As the Universe has stretched and expanded since the Big Bang it has also stretched the wavelength of the radiation emitted when it was very young. So what was once higher-energy, shorter-wavelength radiation now appears as lower-energy, longer-wavelength microwaves. Tiny fluctuations in the density of matter early on in the Universe acted like seeds around which matter began to clump, setting the scene for the formation of vast clusters of galaxies. The fingerprints of these "seeds" can be seen stamped as minute variations in the Cosmic Microwave Background. [2]

The first stars[edit | edit source]

The first stars are thought to have appeared around 200 million years after the Big Bang. They would have been truly gargantuan objects - perhaps 100 to 1,000 times the size of our Sun, and made almost completely of hydrogen and helium. The stars we see today in our own galaxy and in nearby galaxies are totally different from this first generation of stars. This is because over billions of years, generations of stars created and dispersed new chemical elements as they lived and died, enriching the Universe with heavier elements. Carbon,oxygen, iron and silicon were formed from nuclear fusion in the hot cores of the stars, and the very heaviest elements were forged by supernova explosions. As each star dies, it scatters new enriched star firming material across space. Without these successive generation of stars we simply would not be here today, as the ingredients to make us would not exist. [3]

The first galaxies[edit | edit source]

Galaxies are huge collections of stars, and it is thought that the first galaxies began to form sometime around 500 million years after the Big Bang. These early groups would not have looked anything like "modern-day" galaxies such as the Milky Way. Observations made with orbiting telescopes such as the Hubble Space Telescope show that the earliest galaxies were small and irregularly shaped. Studies suggest that these early galaxies underwent vigorous star formation and that they were the building blocks of the galaxies we see today. Over time these smaller galaxies collided and merged together to form much larger galaxies, full of structure, like the ones near us in the Universe that we are able to observe today with amateur telescopes. [4]

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