UNIVERSE. Born of the Big Bang 13.8 billion years ago, the universe has revealed only a small part of its secrets. Size, content, origin and galaxies, we take stock of what we know about the intangible and mysterious universe.
Behind the term “Universe” hides many things. The universe is both the world we live in, but also all that has existed and that which exists. 13.8 billion years ago, it all began with the Big Bang, the birth of the universe and the beginning of its expansion. As it grows, matter and then light emerge, and little by little stars, galaxies, and planets form.
Gradually, astronomers discover the function and physical laws that govern this very complex whole. With the advancement of technologies, space telescopes with unmatched performance, such as the James Webb Telescope, allow us to get ever deeper images of the universe. But what lies behind this so common but also very obscure expression? Where is the Earth in the universe? What is a galaxy? Or is there something after the universe? Let’s take stock of what we know about this group we live in.
The universe corresponds to everything that exists. It is estimated to be 13.8 billion years old. According to the Big Bang theory, the universe was formed from a hot, dense point that suddenly expanded, creating matter, energy, space, and time. The Big Bang theory suggests that this expansion would still be at work today.
How big is the universe?
Current knowledge does not allow us to assess with certainty the shape or size of the universe. However, astronomers have estimated the size of the observable part of the universe, which is a sphere with a diameter of 93 billion light-years.
What is the origin of the universe?
Today we do not know the origin of the universe, and we do not know how to explain its formation with certainty. Scientists must confine themselves to developing theories and proposing scenarios that describe the first moments of the universe and its evolution to the present day. Among these theories, the one that is unanimous among scientists is the theory of the Big Bang.
What is the Big Bang?
The Big Bang is a theory that explains the birth of the universe and its evolution. This model officially saw the light of day in 1927, although it is based on many works and sketches of theories proposed in previous years.
According to this model, the birth of the universe dates back to 13.8 billion years ago. At this point, there is only one microscopic point where pressure and temperature are extremely important. The universe suddenly broke out of this small area and began to swell. The most elementary particles then appeared, gathered to form atoms. Then the light arrived thanks to the formation of photons, which gave rise to the first radiation of light, which is called the fossil radiation.
What is in the universe?
The universe consists of many celestial bodies such as stars, planets, asteroids, comets, etc. All these objects are grouped together in the form of clusters and superclusters, which make up the universe. These clusters are surrounded by empty zones, poor on galaxies. It is said that the universe is a “lacunary” structure, that is, composed mainly of vacuum.
Where can I Find a Map of the Universe?
Cartography of the universe is a discipline in itself called cosmography. It is a disproportionate job that consists of making geography in a dynamic, infinite whole and at inaccessible distances.
Today, the largest 3D mapping of the universe ever produced was completed in July 2020. The result of 20 years of work, this map represents more than 4 million galaxies and quasars, which are particularly luminous stars. Some of these objects are newer, others are older, up to 11 billion years for the oldest of them. The map was presented in the form of a video presentation, which explains the method used to construct these unpublished maps of the universe.
What is the position of the earth in the universe?
The Earth is located in the solar system, a planetary system built around a star: the Sun. This system takes place along with other stars in a galaxy called the Milky Way. If we take a little height, we see that the latter belong to a set of about sixty galaxies called the local group. Associated with other galaxy clusters, the local group belongs to a local superhob, which in itself is only a patch of an even larger superhob. The universe is thus made up of groupings of galaxies of this type, which represent the largest structures that make up the universe.
What is at the center of the universe?
Although we do not know whether our universe is finite or infinite, or what form it has, we are now almost certain that it does not have a center. If the universe is infinite, the concept of center is inconsistent, as there are no edges per. definition. If the universe is limited, space is curved and the universe expands at all points so that it has no center. Nor can it be equipped with edges, as the concept of edges suggests that there would be something around the universe, but the universe is all that exists: therefore there can be nothing around it. .
What is the difference between the galaxy and the universe?
The universe is made up of everything that exists, it is the set of all the structures that we know from the infinitely small atoms of matter, to the large clusters of galaxies of hundreds of millions of years-light. A galaxy is a large cluster of stars contained in the universe. The Milky Way is the galaxy where the Earth and the Solar System are more generally located. Galaxies are therefore structures that are part of the universe.
How many galaxies in the universe?
Current knowledge does not allow us to know the number of galaxies present in the universe with great precision. However, an American researcher, Brian Jackson, from the University of Boise State in the USA, has developed a calculation method that allows him to estimate this value approx. He thus obtained a result of 2,000,000,000,000,000 galaxies in the universe.
There are different types of galaxies, which are characterized by their morphology. There is thus a classification which was devised by the astronomer Edwin Hubble in 1936.
These galaxies have an elliptical shape and can be more or less eccentric, that is, flattened. Depending on this eccentricity, there are subcategories into which they are cataloged. The Cigar Galaxy, located in the constellation Ursa Major, is an example of this type of galaxy.
Spiral galaxies are composed of a luminous bulb surrounded by arms. The latter have different shapes, more or less rolled up, sometimes very loose or even fragmented. The Hubble Space Telescope has photographed a spectacular spiral galaxy called NGC 1300, located just over 70 million light-years from our galaxy.
Lenticular galaxies have a very bright central bulge, but do not have arms like spiral galaxies. This bulb is surrounded only by a simple disc. The galaxy NGC 1947, discovered in 1826, is a lens-shaped galaxy located in the constellation Dorade.
This class includes all galaxies that do not fit into the other categories. There are galaxies without a central bulge or spiral. These are galaxies with a more or less pronounced asymmetry. This is the case, for example, for the galaxy NGC 1569, located in the constellation Giraffe, 11 million light-years from Earth and discovered by William Hershel in 1788.
What is the largest galaxy in the universe?
Until very recently, the largest known galaxy in the universe was called IC 1101. It is an elliptical galaxy discovered by astronomer Hershel in 1790, which is 6 million light-years long. But in 2022, a galaxy that was discovered almost by chance dethroned the previous one. Far from us with 3 billion light-years, Alcyoneus is 16.3 million light-years long. This galaxy is about 160 times larger than the Milky Way.
We know neither the shape nor the boundaries of the universe. On the other hand, scientists identified the boundaries of the visible part of the universe, which is called the observable universe. This zone is bounded by the cosmological horizon. Beyond this limit, the universe continues to expand, but the objects it contains are not visible from Earth because the light they emit has not yet had time to reach us from their training.
It is estimated today that the cosmological horizon is about 45 billion light-years from Earth. However, this limit is dynamic as the light emitted by distant celestial bodies over time ends up reaching us. The observable universe is therefore gradually expanding.
What is after the universe?
By definition, the universe gathers everything that exists, from the smallest structures of matter as atoms to the largest amounts we know: superheaps of galaxies. There is therefore nothing beyond the Universe, since everything that exists is included in it.
Is the universe infinite?
Today we do not know whether the universe is finite or infinite. What we are sure of, however, is that it has no edges, if it had, there would be something beyond the edge. However, the universe encompasses the totality of what exists. It is therefore impossible for it to have an edge. Cosmologists have thus developed different models of infinite universes and finite universes, always without edges.