LC-1-formation-of-the-star-and-evolution

STAR FORMATION AND EVOLUTION

BIG BANG THEORY

  • The universe formation began with the explosion of a primordial atom, known as the Big Bang, approximately 13 billion years ago.

  • This theory explains the continuous expansion of the universe.

Big Bang Characteristics

  • It was not merely an explosion; rather, it involved significant expansion.

  • The universe began as a very hot and dense ball containing a lot of particles.

THE ATOM

Atomic Structure

  • An atom consists of:

    • Protons: Positively charged particles.

    • Neutrons: Neutral particles.

    • Electrons: Negatively charged particles.

  • The nucleus is the central part of the atom where protons and neutrons are located.

  • The number of protons equals the number of electrons in a neutral atom.

Atomic Composition Examples

  1. Beryllium (Be)

    • Protons: 4

    • Neutrons: 5

    • Electrons: 4

    • Atomic Mass: 9.01218 (4 + 5)

  2. Lithium (Li)

    • Protons: 3

    • Neutrons: 4

    • Electrons: 3

    • Atomic Mass: 6.941

BIG BANG NUCLEOSYNTHESIS

  • Following the Big Bang, protons and neutrons combined to create light elements: hydrogen and helium.

  • Other light elements like lithium and beryllium were also formed during this process.

QUESTIONS

  1. What is the most abundant element in the universe?

  2. What do you call the process in which heavier elements (e.g., Lithium and Beryllium) are formed?

  3. Where does the formation of heavier elements take place?

WHAT IS A STAR?

  • A star is a massive ball of gas held together by its own gravitational force.

  • The Sun serves as a model for studying other stars.

  • Stars form from clouds of dust and gas, where gravitational forces pull the clouds together, leading to nuclear fusion reactions.

  • The Sun was formed about 4.5 billion years ago.

HOW ARE STARS FORMED?

  • Outer space has thinly spread gas and dust, known as interstellar medium (ISM).

  • Stars form from the accumulation of these clouds, referred to as molecular clouds.

  • The gravitational energy causes the clouds to collapse, becoming denser, leading to star formation in regions called nebulae (e.g., the Orion Nebula).

STAGES IN THE FORMATION OF STARS

  1. Dark Cloud

    • Size: 200,000 AU

    • Time: 0

  2. Prestellar Core

    • Size: 10,000 AU

    • Time: 10-100 thousand years

  3. Protostar

    • Size: 1,000 AU

    • Time: Up to a million years

  4. T Tauri Star

  5. Pre-main Sequence Star

  6. Main Sequence Star

    • Over 10 million years

PROTOSTAR STAGE

  • When core temperature reaches about 10 million Kelvin, nuclear reactions begin, and the protostar becomes a main sequence star.

EVOLUTION OF STARS

Similar Size to the Sun

  • Stars of similar size evolve as follows:

    • Red Giant Star → White Dwarf → Black Dwarf

Greater Than the Sun in Size

  • Stars much bigger evolve:

    • Red Super Giant Star → Supernova → Neutron Star or Black Hole

EVOLUTION STAGES

Main-sequence Star

  • Core Temperature: 1.5 x 10^7 K

  • Nuclear fusion converts hydrogen into helium, expanding the star.

  • Element formed: Helium (He).

Red Giant

  • Core Temperature: 2 x 10^8 K

  • Converts helium to carbon, inflates due to gravity and fusion reactions.

  • Element formed: Carbon (C).

Supergiant

  • Core Temperature: 7 x 10^8 K

  • Series of reactions lead to formation of heavier elements up to iron.

Supernova Stage

  • Core can't generate enough energy, leading to an explosive supernova.

  • Heavy elements formed during this explosion are released into space.

FUSION REACTIONS

  1. Conversion of Hydrogen to Helium:

    • 4 (H) → He + 2e+ + 2 neutrinos + energy

  2. Helium Fusion:

    • 3 (1½/He) → 12C + energy