Module_3

Formation of Stars and Planets

Overview of the Universe's Origin

• The discussion begins with the final module of the physics component of science, focusing on the formation of stars and planets.

• Previous module covered the origin of the universe, emphasizing the Big Bang theory and the transition into the dark ages.

The Dark Ages and Nebulae Formation

• The dark ages were characterized by clouds of gas formed from scattered hydrogen and helium atoms.

• Atoms gather due to their own gravity, named nebulae (singular: nebula, plural: nebulae).

• This process creates regions in the universe with high density and regions with very low density.

• The imbalance in matter causes variations in gravitational forces in these areas.

Gravity and Gaseous Pressure

• While gravity pulls particles together, gaseous pressure works against this force.

• Gaseous pressure refers to the tendency of gas particles to disperse, similar to the pattern seen when a helium balloon pops.

• Equilibrium exists between the inward force of gravity and the outward force of gaseous pressure.

ProtoStar Formation

• As the mass of gatherings increases, gravity eventually overcomes gaseous pressure, resulting in the formation of a protostar.

• A protostar is the initial stage of star formation where nuclear fusion has not yet begun, but high temperatures develop.

• The protostar phase maintains a temporary equilibrium between gravity and the kinetic energy.

Circumstellar Disks

• As protostars form, a circumstellar disk is created from surrounding materials.

  • Protostellar Disk: Contains materials that will become the star's fuel.

  • Protoplanetary Disk: Contains materials farther out that will eventually collide and form planets.

• The circumstellar disk assumes a flat disc shape due to angular momentum, which is conserved in the system as particles move.

• Angular momentum affects the speed at which materials move relative to their distance from the protostar, with closer materials moving faster.

Stellar Formation Process

• The star formation progresses through several stages:

  • T Tauri Phase: A stage where the protostar evolves, generating stellar winds, demonstrating temperature differences between the core and external areas.

  • Protostellar Jets: Energy and matter are expelled from the poles of the protostar due to stellar winds.

• Chemical reactions caused by protostellar jets may produce bright patches in surrounding areas, signaling the birth of a new star (Herbig-Haro objects).

Composition of Stars

• Stars are formed as gigantic balls of gas and plasma, characterized by various layers:

  • Core: Site of nuclear fusion where lighter elements like hydrogen fuse into heavier elements.

  • Radiative Zone: Energy produced in the core is transmitted outward through radiation.

  • Convective Zone: Energy moves towards the outer layers by convection.

  • Photosphere: The visible surface layer of the star, radiating energy into space.

  • Chromosphere and Corona: Outer atmospheric layers, with the corona being the source of stellar winds.

Life Cycle of Stars

• The life cycle of stars varies based on mass:

  • Low Mass Stars: Evolve through hydrogen burning to helium burning, eventually resulting in a red giant phase, leading to a collapse into a white dwarf.

  • High Mass Stars: Have faster fuel consumption rates due to stronger gravitational forces and can undergo multiple stages of nuclear fusion (carbon, oxygen, etc.) until a supernova explosion results, forming either a neutron star or black hole depending on the remaining core mass.

Star Classification

• Stars can be classified by age and color:

  • Population I, II, and III Stars: Reflect the metallicity of stars, with Population III being the oldest.

  • Color Classification: Related to surface temperature; red stars are cooler while blue stars are hotter, with the temperature represented on the Hertzsprung-Russell Diagram.

Star Systems and Galaxies

• Stars born in nebulae can form star systems:

  • Binary Systems: Consist of two stars.

  • Star Clusters: Groups containing thousands of stars.

  • Isolated Stars: Stars that form alone, often low mass.

• Galactic Evolution: Larger galaxies may form by the collision and merging of smaller galaxies or black holes, leading to complex structures.

The Milky Way Galaxy

• The Milky Way is a spiral galaxy containing 200-400 billion stars, with our sun located in a specific region called the Orion Arm.

• Formation processes include the protoplanetary disk's role in forming our solar system's planets from residual materials.

• Planetary creation resulted in four rocky inner planets and four gas giants, influenced by their proximity to the sun.

• Other materials formed smaller bodies like moons, asteroids, and comets.

Conclusion

• The entire framework from the formation of stars and planets encapsulates the ongoing evolution of the universe, illustrating a continual cycle of birth, life, and death across celestial bodies.