The Heart of a Star: Stellar Nucleosynthesis Fusion Quiz

If two light atomic nuclei combine to form a single heavier nucleus, then a small amount of mass is converted into a large amount of energy. If stars are composed primarily of hydrogen, then this fusion of hydrogen into helium provides the outward pressure to balance gravity. Therefore, nuclear fusion is the primary energy source.

If protons are positively charged, then they naturally repel each other via the Coulomb force. If the temperature is millions of degrees, then the protons move fast enough to get close enough for the "Strong Nuclear Force" to take over. Therefore, high heat and pressure are essential to force the nuclei together.

If a star is relatively small and cool (like the Sun), then it lacks the temperature for complex cycles. If four hydrogen nuclei undergo a series of steps to become one helium nucleus, then this is the p-p chain. Therefore, the p-p chain is the dominant process in our Sun.

If the resulting helium nucleus weighs slightly less than the four hydrogen protons that created it, then that "missing" weight must go somewhere. If Einstein's equation shows that matter and energy are interchangeable, then that missing weight becomes radiation. Therefore, mass is the source of the energy.

If fusing elements lighter than iron releases energy, then the star can stay stable. If fusing iron requires more energy than it releases, then the core will suddenly lose its outward pressure. Therefore, iron is the final element created before a star collapses.

If the early universe contained mostly hydrogen and helium, then all other elements must have been made later. If stars fuse atoms together in their cores over millions of years, then they are "building" the periodic table. Therefore, this process is called stellar nucleosynthesis.

If hydrogen fusion stops, then the outward pressure drops and the core contracts. If the core contracts, it gets even hotter. If it gets hot enough, it can ignite the "ash" left behind by the previous stage. Therefore, the star begins fusing helium into carbon.

If a helium nucleus is also known as an alpha particle, then combining three of them requires a specific three-way interaction. If 3×4=12 (the mass of carbon), then this reaction creates carbon. Therefore, it is the triple-alpha process.

If gravity is crushing the star's mass into a small center, then the density and pressure must be extreme. If fusion is occurring, then the temperature must be millions of degrees. Therefore, A, B, and D are the correct physical conditions.

If every object with mass attracts every other object with mass, then a large cloud of gas will naturally want to shrink. If the cloud shrinks and becomes denser, then it eventually gets hot enough to trigger fusion. Therefore, gravity is the force that starts the life of a star.

If a star has low mass, then its core never reaches the extreme temperatures needed to fuse heavy elements. If a star cannot get hot enough to fuse anything beyond helium, then it stops there. Therefore, only very massive stars can create elements up to iron.

If a star is massive enough, it fuses heavier elements in the center and lighter elements in outer shells. If you look at a cross-section, you see hydrogen on the outside, then helium, then carbon, and so on. Therefore, the arrangement of fusion shells looks like the layers of an onion.

If astronomers plot stars on a graph (H-R Diagram), then most stars fall along a single diagonal line. If these stars are all in the stable middle-age phase of burning hydrogen, then this line is the "main" part of the chart. Therefore, the answer is main.

If a proton turns into a neutron during the first step of fusion, then it must release a positron and a neutral, nearly massless particle to balance the reaction. If this particle rarely interacts with matter and flies straight out of the star, then it is a neutrino. Therefore, B is the correct answer.

If a star is stable, it only fuses elements that release energy (lighter than iron). If Gold requires a supernova to form, then it is not made during stable life. Therefore, Carbon, Oxygen, Neon, and Silicon are the correct choices.

If a star must be at least 8 times the mass of the Sun to become a supernova, then our Sun is too small. If the Sun is a medium-sized star, it will end its life as a Red Giant and then a White Dwarf. Therefore, the Sun will not explode.

If gravity pulls inward, the star wants to collapse. If fusion pushes outward, the star wants to expand. If these two forces are equal, then the star stays the same size and remains stable. Therefore, this balance is hydrostatic equilibrium.

If fusion stops at iron, then heavier elements cannot be made in a stable core. If a massive star explodes, it releases a massive amount of energy and neutrons that can build even heavier atoms. Therefore, the answer is supernova.

If helium is heavier than hydrogen, then it tends to stay in the center of the core where it was created. If it is not yet hot enough to fuse, then it just sits there while hydrogen fuses around it. Therefore, it is often called helium "ash" because it is the leftover of the hydrogen fire.

If the Big Bang only created hydrogen and helium, then all heavier elements must have been made later. If stellar nucleosynthesis is the only way to build carbon from helium, then those atoms had to come from a star that lived and died long ago. Therefore, the statement is true.