To Hand in Essay 5 Where am I going this week? Take 10 minutes to write down your thoughts about Essay 5, your preparation for it, and the end result. Where am I going? What are we looking for? What is the most common element in the Universe? What are we looking for? What is the most common element in the Universe? HYDROGEN! Andromeda Galaxy in Optical Light & Radio (Hydrogen) Same scale! What are we looking for? An atom of hydrogen will randomly give off a wave of radio energy (light!) Every 10 million years. Then how can we possibly see them? ANSWER: LOTS OF ATOMS! The Milky Way contains 3 billion suns worth of hydrogen! Detecting gas, not just starlight Fainter objects that may contain lots of gas Very small dwarf galaxies that might be gas-rich. Are there starless galaxies? Detecting gas, not just starlight Fainter objects that may contain lots of gas Very small dwarf galaxies that might be gas-rich. Why are there so few of them? Of the ones that are left, why