Galaxy Formation & Evolution - The Milky Way contains over 100 billion stars [2] - The sun orbits the galactic center approximately every 200 million years [3] - Galaxies, including the Milky Way, formed and evolved over 138 billion years [9] - Computer simulations allow observation of a galaxy's evolution across billions of years [10] Key Ingredients & Processes - Hydrogen gas and stars are the two most important ingredients in a galaxy [12] - Gravity is the most important law of physics governing galaxy evolution [12] - Galaxies convert hydrogen gas into stars [14] - Supernova explosions, occurring about once per century in the Milky Way, shape galaxies [16] Origin & Implications for Life - The Milky Way was forged in chaos, evolving from many tiny galaxies [18] - Frequent supernova events in the early chaotic phase were not conducive to the emergence of life [22] - Supernova explosions create key elements for life, such as carbon, oxygen, and iron [23] - The Earth and the Sun formed 45 billion years ago after the Milky Way settled into its ordered state [21]