In 1938, German physicist Hans Bethe discovered that stars produce energy through a process of nuclear fusion that turns hydrogen into helium. This releases enormous amounts of energy, but stars use hydrogen very slowly, which is what causes stars to burn for billions of years. For centuries prior to Bethe's discovery, stars were believed to be expressions of the gods and goddesses. The Greek philosopher Anaxagoras was arrested for suggesting that stars were actually masses of rock ripped from the earth that emitted light because they spun around really fast. As science evolved, it surmised that stars were made of combustible rock, like coal, and that they were bright because they were actually on fire. With the development of the spectroscope …show more content…
By 1920, British astronomer Arthur Eddington had already proposed that hydrogen and helium were somehow fusing to produce stellar energy. Bethe simply took that a step further and explained those fusions processes and how stars of different mass engage in different nuclear fusion processes. Bethe's discovery was not made in the laboratory---at least not at first. How protons would react when coming in contact with different protons was already an established part of nuclear physics. In 1938, Bethe applied these principles to explain stellar heat and light in a paper titled "Energy Production in Stars." Thus he's credited with "discovering" stellar nucleosynthesis in 1938, but it wasn't until a decade later, when he was engaged to help develop atomic weapons during WWII that he was able to prove nuclear fusion in the laboratory. According to Bethe's application of nuclear fusion, stars the size of our Sun and smaller generate energy from the proton-to-proton chain reaction. Stars larger than our Sun utilize the carbon–nitrogen–oxygen cycle. In the proton-to-proton chain reaction, two protons smash together to form a neutron called a "deuterium," which is a type of hydrogen. When a third proton attaches, it forms helium plus gamma rays. The gamma rays make their way to the surface of the star in the form of emitted light. The helium atom attaches to fourth proton and the resulting loss of mass produces …show more content…
In the CNO cycle, a carbon nucleus captures a hydrogen nucleus, forming nitrogen plus gamma rays (again, gamma rays make their way to the surface of the star to be emitted as light). The nitrogen nucleus captures another two protons to become oxygen. The nitrogen ejects a proton, converting it back to nitrogen, then breaks down into helium. Again, the resulting loss of mass produces energy. The main difference between whether a star produces energy via the proton-to-proton chain reaction or the CNO cycle is the mass of that star and its heat (which are related to one another). As a result of Bethe's discovery....well, among other things, we got nuclear weapons and nuclear power, but in terms of astronomy, the proton-to-proton chain reaction and CNO cycle opened up the world of stars to further discovery. Astronomers and astrophysicists were able to explain not only that a weak radio signal is coming from the sky---but why (namely, the "flipping" of the hydrogen atom that occurs during stellar nucleosynthesis). Astronomers were able to explain quasars and pulsars, both of which emit radio waves. And stellar science was eventually able to explain black holes, the life cycle of stars, and to hypothesize the eventual fate of our