LECTURE

sequence”) generate energy by hydrogen fusion. They also found stars that did not t this correlation. These were stars at the end of their life cycle. We will discuss them in the next lecture. What the graph shows is that the key determinant of a star’s life is the size of the initial cloud of matter from which it is formed. This determines the pressure in its core and the temperature and speed at which it burns its fuel. This determines how soon it will run through its fuel and die.

Why are stars so important in the modern creation story? First, they represent the rst large, complex objects created by our Universe. Second, stars create the preconditions for new forms of complexity. They do so in two main ways. They pump energy out into the cold empty spaces between them, creating powerful energy ows. These provide the energy needed to create even more complex entities (including planets and even ourselves). They also create new chemical elements needed to form more complex entities (including ourselves). How they do so is the main subject of the next lecture.

This lecture has described how gravity sculpted stars from the simple raw materials of the early Universe. But how did the Universe create even more complex entities such as ourselves? To do that, it had to create more elements. That was the task of dying stars.

Essential Reading

Supplementary Reading

Chaisson, Epic of Evolution, chap. 2. Christian, Maps of Time, chap. 2.

Brown, Big History, chap. 1. Croswell, The Alchemy of the Heavens. Delsemme, Our Cosmic Origins, chap. 2.