Introduction to the Universe

With 2 trillion estimated galaxies and uncountable stars, our Universe is filled with wild examples of exoplanets, stars, black holes, nebulae, galaxy clusters and more, which scientists are still probing.

Our Universe began in a tremendous explosion known as the Big Bang about 13.7 billion years ago. We know this by observing light in our Universe which has travelled a great distance through space and time to reach us today. Observations by NASA’s Wilkinson Anisotropy Microwave Probe (WMAP) revealed microwave light from this very early epoch, about 400,000 years after the Big Bang.

A period of darkness ensued, until about a few hundred million years later, when the first objects flooded the Universe with light. The first stars were much bigger and brighter than any nearby today, with masses about 1000 times that of our Sun. These stars first grouped together into mini-galaxies; the Hubble Space Telescope has captured stunning pictures of earlier galaxies, as far back in time as ten billion light years away.

By about a few billion years after the Big Bang, the mini-galaxies had merged to form mature galaxies, including spiral galaxies like our own Milky Way. It had also expanded, racing under the force of the so-called Hubble constant. Now, 13.7 billion years from the Big Bang, our planet orbits a middle-aged Sun in one arm of a mature galaxy with a supermassive black hole in the middle. Our own solar system orbits the Milky Way’s centre, while our galaxy itself speeds through space.

Under the Milky Way in San Pedro de Atacama, Chile.