Cosmic Composition: From Elements to Solar Systems

Posted on Jan 27, 2025 in Physics

The Universe: Composition and Organization

The universe is composed of approximately 75% hydrogen, 20% helium, and 5% other elements. Dark matter, which we cannot see, makes up 90% of the universe, while visible matter (galaxies, stars, and planets) accounts for only 10%.

Organization of the Universe

  • Universe: A vast collection of billions of galaxies.
  • Super-Virgo Cluster: A group of millions of galaxies.
  • Local Group of Galaxies: A group of about 30 galaxies.
  • Milky Way: Our galaxy, containing approximately 100,000 stars, including the Orion Nebula, Alpha Centauri, and our solar system (Earth and Moon).
  • Andromeda Galaxy: A neighboring galaxy.

The Universe in Motion

  1. Law of Gravitation: All bodies attract each other, with the force increasing as they get closer and their mass increases.
  2. Black Holes: Concentrations of matter with extremely high density, often located at the center of galaxies (e.g., Sagittarius A*).

The Big Bang and the Expansion of the Universe

The universe is believed to have originated approximately 13.7 billion years ago in a massive explosion known as the Big Bang. This is supported by observations of the displacement in spectral lines.

Big Bang History

  1. Stage of Inflation: The super-compressed universe expanded rapidly, reaching a temperature of 1027 degrees.
  2. Formation of Matter: The universe, initially composed of high-energy particles (photons), cooled, leading to the formation of neutrons and protons.
  3. The First Atoms: Approximately 300,000 years after the Big Bang, hydrogen and helium atoms formed.
  4. The Power of the Universe: Charged particles (neutrons, protons) interacted with photons, allowing light to travel through space, making the universe transparent and giving rise to the cosmic background radiation.
  5. Formation of Stars and Galaxies: Dense areas of space with strong gravitational attraction gradually grouped together, forming stars and galaxies.
  6. Dark Energy: An unknown force that counteracts gravitational attraction.

Origin of the Elements

The sun produces helium from hydrogen, while carbon stars produce heavier elements like silicon, iron, and aluminum. Supernovae explosions create the remaining elements due to the immense pressure, energy, and high temperatures.

Solar System Origin

Approximately 4.57 billion years ago, a cloud of gas and dust began to shrink, eventually forming a star and its planets.

  1. A supernova explodes.
  2. The explosion creates a shock wave.
  3. This shock wave approaches a nebula.
  4. The shock wave compresses the nebula, causing it to collapse.
  5. In the center of the nebula, particles collide more frequently, heating the core.

At 10 million degrees, hydrogen nuclei fuse into helium, releasing energy.

Formation of Planets

  1. Approximately 4.57 billion years ago, the nebula compressed, collapsed, and formed a disk.
  2. The disk was hotter in the center, with more particles in each area.
  3. Each area attracted more material, leading to the growth of planets. Outer planets formed first and have more mass.
  4. Small bodies in the disk collided, giving rise to planets like Earth.
  5. Excess material formed satellites.

Outer Planets: Jupiter, Saturn, Uranus, Neptune

Inner Planets: Mercury, Venus, Earth, Mars

Exoplanets: Planets that do not orbit our sun.