Image source [1]: The Hubble eXtreme Deep Field (XDF) was completed in September 2012 and shows the farthest galaxies ever photographed. Except for the few stars in the foreground (which are bright and easily recognizable because only they have diffraction spikes), every speck of light in the photo is an individual galaxy, some of them as old as 13.2 billion years; the observable universe is estimated to contain more than 2 trillion galaxies.
Hi friends, today we are going to talk about Cosmology but before going into the subject we are going to see these two important definitions in astrophysics.
Synchrotron radiation (also known as magnetobremsstrahlung radiation) is the electromagnetic radiation emitted when charged particles are accelerated radially, i.e., when they are subject to an acceleration perpendicular to their velocity. It is produced, for example, in synchrotrons using bending magnets, undulators and / or wigglers. If the particle is non-relativistic, then the emission is called cyclotron emission. If, on the other hand, the particles are relativistic, sometimes referred to as ultrarelativistic, the emission is called synchrotron emission.
Image source [2]: Synchrotron radiation from a bending magnet.
When an electron starts spinning around the magnetic field traveling a helical path, it is being accelerated. In effect, it does not follow a straight path, then there is an acceleration. An accelerated electron emits electromagnetic radiation and the radiation corresponds to the so-called synchrotron radiation. Electrons with moderate speeds, or thermal electrons, emit very little, but the relativistic electrons of cosmic rays produce a synchrotron radiation that dominates the continuum of radio waves. The intensity of the radiation depends on the magnetic field, the density of relativistic electrons and the energy of these.
Galaxy groups and clusters are the largest known gravitationally bound objects to have arisen thus far in the process of cosmic structure formation. They form the densest part of the large-scale structure of the Universe. In models for the gravitational formation of structure with cold dark matter, the smallest structures collapse first and eventually build the largest structures, clusters of galaxies.
Image source [5]: Galaxy cluster ACO 3341 seen by VLT's VIMOS.
Image source [6]: Galaxy Cluster LCDCS-0829 acting like a giant magnifying glass. This strange effect is called gravitational lensing.
There are clusters of galaxies, supercumuli, which are clusters of galaxy clusters and a large-scale structure formed by the set of supercumuli. Some clusters are small, as a local group, to which the Milky Way belongs. It is formed by little more than 20 galaxies, among which the most important are M31 (Messier 31), M33 (Messier 33) and the Milky Way. The supercumuli are grouped forming enormous filaments of matter. The filaments join with each other forming polyhedrons, which in turn, are part of a surprisingly crystalline structure, which suggests a three-dimensional chess, although the available data are still few. The regularity of the network that characterizes the structure is also seen in the distribution of the quasars.
Cosmology: Newtonian cosmology
Cosmology is the study of the origin, evolution, and eventual fate of the universe. Physical cosmology is the scientific study of the universe's origin, its large-scale structures and dynamics, and its ultimate fate, as well as the scientific laws that govern these areas.
The cosmology studies the evolution of the universe and the universe is by definition, everything. The cosmology requires the general Relativity and, especially in the most primitive stages, the physics of elementary particles. However, Newton's mechanics allows us to get into the essential and, what is more interesting, provides the same equations, correct and corroborated by Relativity.
The Cosmological principle
In modern physical cosmology, the cosmological principle is the notion that the spatial distribution of matter in the universe is homogeneous and isotropic when viewed on a large enough scale, since the forces are expected to act uniformly throughout the universe, and should therefore produce unobservable irregularities in the large-scale structuring over the course of the evolution of the matter that was initially laid down by the Big Bang.
Aristarchus and Copernicus taught us that the earth is not the center of the solar system. Today we know that the sun is any star of any galaxy. If we want to think about the universe, we need to assume that our particular corner of observation does not give us a particular view of it. Our point of observation is any point. This is philosophically attractive, so we assume the so-called cosmological principle that says: "The Universe is homogeneous and isotropic." All the magnitudes like pressure, temperature, chemical composition, etc., do not have gradients. They have the same value in all points of the universe (homogeneity). We always observe the same thing, in any direction (isotropy).