Universe, Stars, and Galaxies: A Cosmic Journey
Spectra
Isaac Newton discovered that sunlight, when incident on a glass prism, decomposes into colored stripes. This rainbow is called the spectrum of light. Technical improvements revealed black lines within the spectrum. The Sun, being the nearest star, provides a light spectrum that offers information about its elemental composition. By comparing the black lines in the Sun’s spectrum with those of hydrogen and helium, we can conclude that the Sun’s outer layers are primarily composed of these two elements. This procedure allows us to identify elements and compounds in other stars and galaxies.
Organization of the Universe
The Milky Way is part of a group of about thirty galaxies called the Local Group. This Local Group, in turn, belongs to a larger set of groups known as the Virgo Supercluster, comprising thousands of galaxies and trillions of stars. It’s possible that the Virgo Supercluster is part of an even larger structure. The Sun is an average star with planets, situated in an intermediate zone of a large spiral galaxy we call the Milky Way. On very dark nights, we can see a section of our galaxy. All the stars we see with the naked eye belong to the Milky Way. Constellations are groups of stars forming characteristic shapes and bearing specific names. However, most constellations are not actual groups; the stars within a constellation are not all at the same distance from Earth.
Black Holes
The most intense gravitational attraction occurs in black holes, regions of extremely high density. Their gravitational field is so strong that not even light, with its extraordinary speed, can escape.
The Big Bang
Inflation
The super-compressed universe expanded at an incredible speed. The temperature was approximately 1027 degrees.
Formation of Matter
The expanding universe consisted of subatomic particles (electrons, quarks, protons, and neutrons) bathed in vast amounts of energy: photons.
The First Atoms
About 300,000 years after the Big Bang, hydrogen and helium atoms formed, in percentages very similar to those observed today.
The Power of the Universe
Charged particles initially interfered with photons. But when these particles combined to form atoms, light could travel freely in the newly created space. The universe became transparent, and the cosmic background radiation emerged.
The Dark Energy
Galaxies are moving at increasing speeds. The cause is believed to be dark energy, a mysterious force that counteracts gravitational attraction.
Formation of a Star
The universe consists of galaxies, which are composed of stars. Stars are masses of gas that emit light. The gas forming a star constantly shrinks due to gravity. As it contracts, the temperature rises until it reaches 1,000,000 °C. Then, nuclear reactions begin, converting hydrogen into helium and emitting high energy, which counteracts the contraction. When all the hydrogen is consumed, the star becomes a “red giant,” reaching its maximum size. If the star was massive, it explodes in a “supernova.” If it was smaller, it’s called a “nova.” Supernovae release a huge amount of material, which can collapse to form a black hole. Some parts of the universe have planets orbiting stars, satellites orbiting planets, and nebulae (clouds of gas).
Origin of the Solar System
Catastrophe Theory (16th Century): A collision between two stars.
Laplace Nebular Theory: A nebula began to contract, increasing its spin and angular momentum, and expelling swirling mass. This stellar mass began to rotate in orbit. The nebula shrank, possibly triggered by a supernova explosion.