Space and the Universe Lecture Notes

Introduction

• Exploration of space begins from Earth, a colorful and diverse planet.
• Space is vastly empty with a low density of matter.
• Large telescopes like the James Webb Space Telescope reveal the wonders of space.
• James Webb Deep Field: Images showing light from galaxies shortly after the Big Bang.
• Focus on decoding and modeling the light of galaxies to understand astrophysics.

Understanding Galaxies

• The Milky Way: Our home galaxy, visible with high density of stars from the Southern Hemisphere.
• Galaxy Structure:
  • Contains numerous stars.
  • Structure: Disk, bulge, and nucleus.
  • Black holes located at the center.
  • Surrounded by dark matter.
• Types of Galaxies:
  • Ellipticals: Spherical, likely formed first after the Big Bang.
  • Spirals/Disk Galaxies: Have spiral arms like the Milky Way.
  • Dwarfs: Small, low star content, sustained by dark matter.
  • Mergers: Galaxies interacting with each other.

Formation and Evolution of Galaxies

• Big Bang Model: Proposed by George Lemaître, explaining the universe's expansion.
  • Starts from singularity and expands rapidly (inflation).
  • Cosmic hot soup: High temperature environment with elementary particles.
  • Cooling allows formation of hydrogen atoms.
• Expansion and Dark Matter:
  • Universe's expansion is accelerating.
  • Gravitation and dark matter are crucial for galaxy formation.
  • Dark matter: Hypothetical, unseen substance necessary for galaxy formation.
• Cosmic Pie: Composition of the universe with a large portion being unknown (dark matter and dark energy).

Observational Evidence and Modeling

• Vera Rubin: Demonstrated need for dark matter through galaxy rotation curves.
• Dark Matter Modeling:
  • Large simulations like the Millennium Simulation help understand dark matter.
  • Contributions of dark matter to galaxy formation and structure.

Light and Spectral Analysis

• Stellar Light: Key to understanding galaxies as it provides chemical and physical information.
• Spectrum Analysis:
  • Example: M87 galaxy's spectrum showing chemical elements.
  • Modeling spectral energy distributions to understand galaxy properties.

Star Life Cycle and Stellar Populations

• Star Types and Lifecycles:
  • Stars shine by converting hydrogen into helium (Einstein's equation).
  • Stars vary in size and lifespan, influencing galaxy light.
• Population Synthesis:
  • Modeling star populations in galaxies to simulate their light.
  • Challenges include initial mass function and computational needs.

Future of Galaxies and Cosmic Time Machine

• Galaxy Evolution:
  • Galaxies will eventually consume all their gas and dim.
  • Milky Way to collide with Andromeda in 3.5 billion years.
• Cosmic Stroll App:
  • Allows visualization and exploration of distant galaxies.

Conclusion

• Modern scientific tools and models provide insights into galaxy formation and evolution.
• Light from galaxies helps decode cosmic history and understand the universe's structure.
• Astrophysics continues to explore unknowns like dark matter and dark energy.