Chapter 12: Problem 2

Describe the steps leading up to a core-collapse supernova?

Short Answer

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Question: Briefly explain the critical stages and processes that lead to a core-collapse supernova in a massive star.

Step by step solution

Stellar Lifecycle

Begin by understanding the life cycle of a massive star (those with >8 solar masses). A star begins from a protostellar gas cloud composed mainly of hydrogen and helium. Under gravitational collapse, the core of the cloud heats up and begins nuclear fusion, a process called the main sequence. The fusion of hydrogen to helium in the core generates pressure and thermal energy, counteracting gravitational forces.

Post-main Sequence

After the hydrogen in the core has been nearly depleted, the fusion stops, and the core contracts due to gravity. The outer shell starts to expand, and the star turns into a red supergiant. During this phase, hydrogen fusion moves to a shell surrounding the core. In the core, helium begins to fuse into heavier elements, like carbon and oxygen, through a process called the triple-alpha process.

Fusion of Heavier Elements

As the core contracts, it heats up due to increasing pressure and temperature. When the core is hot enough, fusion reactions can continue for progressively heavier elements like neon, magnesium, silicon, and sulfur. Each stage creates energy and builds up heavier elements, forming a layered structure in the core. This process continues until the formation of iron in the core.

Iron Core Formation

The formation of an iron core is a crucial turning point in the star's lifecycle. Iron does not produce energy by fusion due to its high nuclear binding energy. Once the iron core reaches its Chandrasekhar mass (approximately 1.4 solar masses), electron degeneracy pressure cannot support the core against gravity, and it starts to collapse.

Core Collapse

The core collapses rapidly under gravity, taking less than a second. The density and pressure at the core's center increase drastically. The remaining electrons and protons combine to form neutrons and neutrinos. Neutrinos, being weakly interacting particles, escape the core, taking away a significant amount of energy.

Formation of Neutron Star or Black Hole

As the core collapses, the outer layers fall inward and collide with the dense neutron core. The shockwave caused by this collision rebounds outward, resulting in a powerful explosion called a supernova. The remnants of the core are compressed further due to gravity, forming a neutron star if the core mass is between 1.4 and ~3 solar masses. If the mass is higher, the core will continue to collapse and create a black hole.

Core-Collapse Supernova

The core-collapse supernova is a spectacular event that occurs during the explosive phase. The outer layers of the star are expelled into space at high speeds, creating an expanding shell of gas and dust known as a supernova remnant. As the shell expands, it interacts with the surrounding interstellar medium and emits intense radiation, making the core-collapse supernova observable across the universe.

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Describe the steps leading up to a core-collapse supernova?

Short Answer

Step by step solution

Stellar Lifecycle

Post-main Sequence

Fusion of Heavier Elements

Iron Core Formation

Core Collapse

Formation of Neutron Star or Black Hole

Core-Collapse Supernova

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