🌺 The UNIVERSE CONTAINS EVERYTHING that exists , from the tiniest subatomic particles to galactic superclusters ( the largest structures known ). Nobody Knows how big the Universe is , but astronomers estimate that if contains at least 125 billion galaxies , each comprising an average of 100 billion stars . The most widely accepted theory , which states that the Universe came into being in a huge explosion - the Big Bang - that took place between 10 and 20 billion years ago. The Universe intially consisted of a very hot , dense fireball of expanding , cooling gas .After about one million years , the gas began condense into localized clumps called protogalaxies. During the fnext five billion years , the protogalaxies continued condensing , forming galaxies in which stars were being born. Today , billions of years later , the universe as a whole is sti expanding , although there are localized areas in which objects are held together by gravity ; for example , many galaxies are found in clusters. The Big Bang theory is supported by the discovery of faint , cool background radiation coming evenly from all directions. This radiation is believed to be the remnant of the radiation produced by the Big Bang. Small " ripples" in the temperature of the cosmic background radiation are thought to be evidence of slight fluctuations in the density of the early Universe , which resulted in the formation of galaxies .Astronomers do not yet know if the Universe is " closed " , which means it will eventually atop expanding and begin to contract , or if it is " open " , which means it will continue expanding forever'.
🌺 Types of galaxy
🌺 NGC - 4406 (Elliptical galaxy)
🌺 NGC - 5236 ( Barred Spiral Galaxy)
🌺 NGC 6822 -( Irregular Galaxy)
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