In New York, we don’t have a particularly clear sky. If we’re lucky, we can catch glimpses of constellations and observe the solemn wanderings of the planets across the cosmic tapestry. But when we do see some stars, it is only natural to wonder about their origins. Where did they come from?
To understand how stars form, let’s consider the star nearest to us: the Sun. If we turn back the clock approximately 4.5 billion years, we would see a very different star, one shrouded in clouds of gas and dust. In addition, we would see other stars in the stellar neighborhood. Like our Sun, these stars formed from the surrounding material. Perturbations in an otherwise relatively homogenous cloud of gas and dust allow for the collection of matter in an increasingly dense region. When the collection becomes dense enough, the protostar begins to glow in the infrared. In addition, a ring of material known as an accretion disk begins to form. This ring can also glow due to friction as small pieces of matter rotate rapidly around the forming the star. As the protostar grows in mass, it begins to radiate more energy. Eventually, fusion ignites in the core and hydrogen fuses to form helium. Currently, the Sun uses 620 million metric tons of hydrogen each second to maintain nuclear fusion!
The ignition of nuclear fusion creates a powerful solar wind that clears out a bubble whose boundary is heavily ionized (meaning that the radition emitted by the star alters the charge of atoms in the surrounding gas). When the dust is cleared away, a new star is revealed with its proto-planets (if it has any).
You may ask why I called nebulae the “Cage of the Stellar Phoenix”. This is because stars behave, in a way, like phoenixes (the mythical bird that can burst into flames and emerge from the ashes as a newborn). The final stage of a star’s life is known as a supernova. It is a culminating moment after billions of years of using up nuclear fuel. When nuclear pressure fails to support the star against the crushing gravitational force, the star collapses and releases its constituents into the surrounding region of space in a flash that can be as bright as trillion suns. The gas and dust released from this explosion contains most of the heavy elements found in nature and provides for the environment necessary for the next generation of stars to form. It would be interesting if we could figure out our Sun’s stellar family tree, going back to the very first stars in the Universe!
