Understanding the Universe: Structure, Stars, and Big Bang
Structure of the Universe
The universe is composed of an enormous vacuum in which billions of galaxies float. In each galaxy, there are billions of stars, planets, and nebulae. Chemically, the universe is composed of approximately 75% hydrogen, 20% helium, and 5% other elements. In addition to the observable matter, there is non-observable matter (dark matter), which constitutes 90% of the universe’s matter.
To measure distances in the Universe, the unit known as a light-year is used. A light-year is the distance light travels in one year. The speed of light is 300,000 km/s.
The Solar System consists of a star (the Sun) and planets revolving around it, along with other celestial bodies such as comets, satellites, and asteroids. The Sun is one of the 100,000 million stars that are part of the Milky Way galaxy. The Solar System is located at one end of one of the Milky Way’s arms: the Orion Arm. The Milky Way is part of a group of galaxies that are relatively close to each other: the Local Group. The Local Group is part of a broader structure: the Virgo Supercluster.
Determining the Composition of Stars
Since the 17th century, Isaac Newton discovered that light breaks down into stripes of different colors when passing through a prism: the light spectrum. Further refinement of the technique revealed black lines in this spectrum.
If we pass light through containers of certain chemical elements (e.g., hydrogen or helium), the spectrum of light shows dark lines, indicating that there has been an absorption of light in certain parts of its spectrum. These absorption spectra are characteristic of each chemical element. By comparing the spectrum of light from a star with the absorption spectra of known elements, we can deduce the star’s chemical components.
A Universe in Motion
The entire universe is in constant motion. Planets revolve around stars, stars orbit the center of galaxies, and galaxies are moving away from each other. The greatest gravitational attraction is given by black holes, which are concentrations of matter with very high density. They are formed from the collapse of massive stars (several times the mass of the Sun).
Their discovery is due to the fact that they are sources of X-ray emissions, produced by the acceleration of material falling into the black hole. Their density is so high that not even light can escape them, and they can distort space-time. Everything within a distance of 7.7 million km is swallowed by the black hole. At the center of our galaxy, there is a supermassive black hole, Sagittarius A*, around which the galaxy rotates.
The Big Bang
Approximately 13.7 billion years ago, all matter in the universe was condensed into a relatively small area (the Cosmic Egg). There was a massive explosion (the Big Bang), and as a result, the present universe was formed. The Big Bang theory was formulated to explain an observation: the spectra of more distant galaxies were displaced, exhibiting a redshift. To explain this, the Doppler effect must first be understood.