The Universe | Galaxies | Big Bang Theory

Universe:

Universe is simply one word to describe all time and space. Technically it is the collection of all the galaxies, planets, contents of intergalactic space and all form of matter and energy. It is said, however, the Universe is infinite but some scientific researches claims at its almost 91 billion light years in diameter. Every age came up with the different definition of Universe; the scientific researchers have been engaged in unveiling the secret of the Universe. In the wake of this, in 1990, the scientists discovered Cosmic Microwave Background Radiation which spells out that the Universe is expanding and hence has a begging and an end. So far there is a lot in the universe which is unknown to human which is termed as Dark Matter. Out of numerous cosmological models, the Big Bang theory is considered to be the best and most effective in defining the formation of Universe [Given in detail below]. If the Big Bang theory is correct then the estimated age of the Universe is about 13.79 billion years.

Galaxy:

A galaxy is a massive, gravitationally bounded system that consists of stars and stellar remnants, planets and material left over from their formation, an interstellar medium of gas and dust, and the unknown dark matter and energy orbiting around a common center of mass.

The number of stars in a galaxy typically ranges from dwarf galaxies that contain less than ten million stars to giant elliptical galaxies that contains up to a trillion stars.

There are more than 150 billion galaxies in the observable universe. Most galaxies are 3300 to 330,000 Light year across and are separated by millions of light year. The space in between galaxies is filled with essentially a vacuum (1 atom per cubic meter).

Galaxies are found in clusters that jointly make a super cluster. The Super Clusters are generally arranged into sheets and filaments which surround immense voids in the universe. Since there is no wall/fence between two galaxies so they can interact with each other and such interaction is known as Galactic Evolution. Such interaction may cause changed shape of galaxies however, in some cases the size of one galaxy is too big to be affected by interaction, it is called Cannibalism.

Classification of Galaxies:

The classifications of Galaxies are based on appearance and not characteristics, behavior or any strangeness that might show in the galaxy. The classification does not account for irregulars or other types of galaxies only spiral and elliptical.

(i) Spiral Galaxy: Disk-shaped with curving, dusty arms.

(ii) Elliptical Galaxy: Elliptical-shaped with little dust and no arms.

(iii) Irregular Galaxy: Irregular or unusual shape and usually result from collisions or disruption from the gravitational pull of near-by galaxies.

Big Bang Theory:

The Big Bang theory is the prevailing cosmological model for the universe from the earliest known period through its subsequent large-scale evolution. The model accounts for the fact that the universe expanded from a very high density and high temperature state and offers a comprehensive explanation for a broad range of phenomena including the abundance of light elements, the Cosmic Microwave Background Radiation, large scale structure and Hubble’s Law. If the known laws of physics are extrapolated to the highest density regime, the result is a singularity which is typically associated with the Big Bang. Detailed measurement of the expansion rate of the universe place this moment at approximately 13.8 billion years ago; which is thus considered the age of the universe. After the initial expansion, the universe cooled sufficiently to allow the formation subatomic particles (e.g. Electron, Neutron, Proton) and later simple atoms. Giant clouds of these primordial elements later coalesced through gravity in halos of dark matter, eventually forming the stars and galaxies visible today.

Black Holes seem to be found in the center of a number of large galaxies.

Dark Matter, according to the current hypothesis, sees to account for about 90% of the material in a galaxy.

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