The core of the globular cluster NGC 6397 looks like a chest full of glittering jewels. It is located 8,200 light years towards the southern constellation of Ara, and is among the closest to the Solar System. The stars are here very close together, with a space between them of a few light-weeks, while four light-years separate us from the closest star to the Sun, Alpha Centauri.
Basic Universe Universe comes from the Latin "universus". It is usually defined as the set of all created things (if created in creation), or of all things that exist. We usually use words such as "universe", "universal" or "universality" to refer to a fact or idea that encompasses everything, although, often, we refer to something that does not go beyond our planet, such as "a universe of options, or when we name a "universal" artist, or we refer to the "universality" of laws, phenomena or cultural events.
Advanced Universe Knowledge about our Universe has many levels. If the previous chapter, "Basic Universe", dealt with elementary aspects, in this we will go deeper. Of course, without scientific or professional pretensions since, as indicated by the title of the site, it is about educational astronomy.
Shape of the Universe The shape of the Universe we inhabit is a very important issue for Cosmology. The final destiny of the Universe itself depends on the form it has. However, even today the shape of the Universe is impossible to find out. The shape of the Universe depends on its density, that is, on the amount of mass and energy it possesses.
Active galaxies Galaxies are not stable, on the contrary: they grow and move, that is, they are active. Some more and others not so much. Almost all galaxies have a black hole in their center. While the black hole is active, it catches and engulfs all the matter around it, like a whirlpool. When the black hole of an active galaxy no longer has the capacity to swallow more, matter continues to revolve around it, but it no longer falls inside.
The matter of the Universe Matter is everything that has mass. All matter is made up of particles. They are like tiny pieces that come together to form everything we see. Although they also form another type of matter that we cannot see, dark matter. In fact, most of the matter that makes up the Universe is dark matter.
The Universe What is the Universe? How is it? Why does it exist? How did it come about? Many of the questions that human beings have asked themselves since their evolution began concern the world around us. In the following pages we will search and study the answers. As knowledge increases, the Cosmos expands.
Variable stars The concept of variable stars encompasses any star whose brightness, seen from Earth, is not constant. They can be stars whose light emission really fluctuates (intrinsic), or stars whose light is interrupted in their path to Earth, by another star or a cloud of interstellar dust, called extrinsic variables.
Observation of the Cosmos Since its origins, the human species has observed the sky. First, directly, then with increasingly powerful telescopes. Now, with many electronic means. Ancient civilizations grouped the stars into figures. Our constellations were invented in the eastern Mediterranean about 2 years ago.
The Galaxies of the Universe The galaxies of the Universe are huge accumulations of stars, gases and dust. In the Universe there are hundreds of billions of galaxies. Each one can be formed by hundreds of billions of stars, nebulas, black holes and other stars. In the center of the galaxies is where more stars are concentrated.
Size of the Universe The Universe encompasses all that is known: matter, energy, space and time. The scales in the universe are so great that we can't even imagine them. To get an idea, for every grain of sand on Earth, there are a million stars, or more. Our galaxy is only one among hundreds of billions of galaxies.
The Local Group The nearby galaxies are attracted by their gravity and are grouped into clusters. Smaller clusters are called groups. Our galaxy belongs to one of these groups: the so-called Local Group. The Local Group has a diameter of 4 million light years and gathers about 40 galaxies. This is a still young cluster that is part of an even larger structure, called Virgo Supercluster.
Clusters of galaxies Clusters of galaxies are gigantic structures of the Universe. Galaxies emit a lot of gravity. This causes nearby galaxies to attract each other and group together to form clusters. Our galaxy, the Milky Way, is part of a small cluster called the Local Group. Within a cluster, galaxies revolve around each other, and they even frequently collide.
The faraway galaxies The farthest galaxies are more than 13,000 million light years from our Milky Way, almost at the edge of the visible Universe. Its light has taken all that time to reach us. This means that we see them as they were more than 13,000 million years ago, only 500 million years after the Big Bang.
Models of the Universe Traditionally, cosmology imagined the Universe as a linear model. That is, a unique Universe with a beginning and probably an end. For the linear model, the Big Bang is the beginning of everything: space, time, physical laws and all matter and energy. If this is true, there is only one Universe and it encompasses everything that exists.
The observable Universe Even with the most advanced technology, we can only see a small part of the Universe. It is called the observable Universe, and it is the part of the Cosmos whose light has had time to reach us. The observable Universe is shaped like a sphere, with the Earth at its center. So we can see the same distance in all directions.
Types of particles in the Universe All matter that exists in the Universe is made up of particles. Each type of particle fulfills a different function. The interaction between different types of particles makes the Universe possible as we know it. There are two kinds of particles: fermions and bosons.
Cosmic radiation All visible objects in the Cosmos, from planets to galaxy superclusters, emit some kind of radiation. This radiation is energy that travels through space. The light we see is a small part of that radiation, which our eyes can perceive. There are (that is, we know) two types of cosmic radiation: electromagnetic radiation and cosmic rays.
Structures of the Universe The matter of the Universe is ordered. The force of gravity causes matter to be grouped into structures. From the simplest, such as stars or solar systems, to the gigantic walls of galaxies. Even so, the expansion of the Universe makes the different structures move away from each other at great speed.
Double stars A double star is a pair of stars that are held together by the force of gravitation and revolve around their common center. Double (or binary) stars are very frequent. Orbital periods, ranging from minutes in the case of very close couples to thousands of years in the case of distant couples, depend on the separation between the stars and their respective masses.
Wormholes A wormhole is a tunnel that connects two points of space-time, or two parallel universes. One has never been seen and it is not proven that they exist, although mathematically they are possible. They are called that because they resemble a worm that crosses an apple inside to reach the other end, instead of running it outside.