GALAXY-THE UNIVERSE-2

GALAXY-THE UNIVERSE-2


Our universe consists of solar systems, stars and galaxies. Galaxies are huge congregations of stars that are held together by own gravity. Because of their huge size galaxies are also called as Island Universe. Every galaxy is composed of about 100 billion stars.

A galaxy, in general, is a constellation of stars. The centre of the galaxy is bulge and its three rotating arms. The stars are present in the arms of the galaxy but the concentration of the stars is high in the centre i.e bulge area of the galaxy.

FORMS OF GALAXIES

  • SPIRAL GALAXY– The spiral-shaped galaxy is disc shape and have tow or more arms rotating about the central bulge. Example- Milkyway and Andromeda.
  • BARRED SPIRAL-The barred shaped galaxy has a rigid bar at the centre with spiral arms. the bar rotates and acts as a nucleus. It has millions of stars.
  • ELLIPTICAL GALAXY– The elliptical-shaped galaxy is elliptical in shape and has no arms. The galaxy range in shapes from spherical, elliptical to extremely saucer-shaped.
  • CANNIBAL GALAXY– Cannibal galaxy is an elliptical galaxy but are so large that they exert a huge gravitational pull which makes them swallow up the small galaxies.
  • IRREGULAR / AMOEBA GALAXIES– The galaxies which have no definite shape and are small in size are known as irregular or amoeba galaxy. Inside this galaxy, the new stars are continuously formed and are full of gas and dust. Limon Alfa Blobs is amoeba in shape is composed of galaxies having a width of 20 crore light-years.
  • MILKYWAY / MANDAKINI– The Milkyway or Mandakini is the name of our galaxy to which our solar system belongs. A spiral-shaped galaxy which belongs to a cluster of 24 galaxies called ” the local group” that moves together. It is called Milkyawy or Akash Ganga because of a peculiar feature is a band of light made up millions of star running almost in a circle through it. This band of light gives it the name Milkyway or Akash Ganga. The main body of the galaxy is a disc 100,000 light-years across with a globular nucleus of about 16,000 light-years in diameter with stretching spiral arms. The distance of the galactic nucleus is about 32,000 light-years from the sun. The black hole in the galaxy is inactive.
  • ORION NEBULA– The brightest and the coldest group of our galaxy.
  • SIRIUS / DOG STAR– It is 9 years away from the earth and has a mass two time that of the sun. It is 20 times brighter than the sun and is the brightest star seen in the night.
  • PROXIMA CENTAURY– The star is the nearest to the sun, about 4.3 light-years away from the sun.

STAR AND ITS LIFE CYCLE

A star is a large ball of gases which emits their own light. Star is composed of hydrogen which under gravitational pull results into nuclear fusion reaction. Through nuclear fusion, the hydrogen present in the star gets converted into helium and a tremendous amount of energy is released. Stars account for 98% of the matter in a galaxy. The other 2% consists of interstellar or galactic gas and dust in very attenuated form.

  • BIRTH OF A STAR– The stars are made up of hydrogen and dust particles. This cloud is called Nebulae. This nebula collapse under gravitational force and results in the formation of a Protostar. This protostar collapses further and forms a chain of stars. In this process, an enormous amount of energy is released in the form of light and heat. gradually a stage is reached when this gaseous mass becomes a star.
  • RED GIANT STAR– The hydrogen present at the centre of the star gets converted into helium and the star starts contracting under its own gravity. Simultaneously the hydrogen present in the outer layer continues the process of the fusion. Therefore it results in an imbalance in the gravitational pull of the centre and an enormous amount of energy is produced in the outer layer, the star expands to a large size. The temperature of the star falls and it becomes red in colour. This stage is called the red Giant Star. From this stage onwards the future of the star depends upon its initial mass. At this stage, the helium gets converted into carbon and carbon gets converted into heavy metal iron.
  • WHITE DWARF / FOSSIL STAR– If the initial mass of the is less than 1.4 of the solar mass i.e the mass of the sun then the life of these star ends as a white dwarf star. If in case the mass of the star exceeds the limit of 1.4 of the solar mass then it will end in a black hole. The limit of 1.4 is Chandrashekar Limit. It was given by Dr Subramaniam Chandrashekar, an Indo-American astrophysicist.
  • SUPERNOVA– The white dwarf star turns into a black dwarf. If the mass of the star is much more than the mass of the sun then it becomes a Neutron Star. The spinning of a neutron star around its axis is known as Pulsar. The neutron star continues to contract and concentrate it on one point it is called Black Hole. The black hole continues to shrink and it explodes in the form of Supernova. The death of a star.

Madhvendra Mishra

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