Nebula, Galaxies & Type of Galaxies UPSC

The Sanskrit word ‘Nihar’ means – fog. That’s why the light beam which looks like fog or smoke in the sky is called nebula. Nebula is called Nebula in Latin terminology; Gone. Until recently, nebula and galaxy were used as synonyms. But now the words nebula and galaxy denote different meanings.
Actually the beginning of the formation of a galaxy is hydrogen. It is caused by the accumulation of a huge cloud made of gas, which is designated by the noun of Nebula. Gradually, clumps of gas developed in this growing nebula. These clusters became increasingly dense gaseous bodies, from which the formation of stars began, that is, the system of stars, dust particles and gases bound under the force of gravity was given the name of galaxy. Thus, the nebula signifies the embryonic state of the galaxy, while the word galaxy refers to the developed state.
The galaxy in which our solar family is located is called ‘Milky Way (Mandakini)’. * The part of Mandakini which is visible from the earth like a light source is known by the name of ‘Swarg ki Ganga’ (Milk Way). That is, we cannot see the entire Mandakini from the Earth, but only a part of it, which is called the Milky Way.

Our universe was born as a result of the Big Bang. There are more than one trillion (100 million) galaxies in the universe. Of this, 10 billion galaxies can be seen with a telescope. These galaxies are made of large clusters. There are many galaxies in a super cluster of galaxies. According to astronomer Harlow, any galaxy first starts irregularly and assumes a spiral shape. Eventually, after the growth of stars, it turns into an elliptical galaxy. Different types of radiation keep emanating from the galaxy. These include gamma rays, infrared rays, radio waves, ultraviolet light, visible light and x rays etc. With the help of these radiations, their study is possible.

Mandakini Galaxy

The galaxy in which our Sun, Earth, planets and satellites are located is called Mandakini. * This is a large cluster of 24 galaxies. * In which the shape of our ‘Mandakini’ galaxy is spiral. * About one trillion stars are found in it. It is flat like a saucer, it has three rotating arms (Spiral Arms). * Its expansion is 80 thousand light years, its center is called Bulge, in which a black hole (Krishna Vivar) is found. Due to gravity, the concentration of stars is high here. Recent research has shown that a quasar is found in the bulge. Black hole is found in the center of the quasar itself.

Many black holes are found in the universe, which act as the center of gravity for the operation of our universe. We cannot see them because light does not emanate from them. But in this, energy is emitted in the form of x-rays from the collapsing matter, which gives the impression of the presence of a black hole. Although a black hole is more than 3 times larger in mass than the solar system. But it emits more energy than the energy released from the entire galaxy.
Surrounding the central bulge is an intermediate rotating arm consisting of relatively young stars. Our solar system is located in this arm. * The distance of Sun from the center of Mandakini is 32000 light years. Sun completes one round of Mandakini’s center in 25 crore years.
Clouds of gas and dust are found in the third rotating arm of Mandakini. New stars are born here.

Constellation of Stars

constellatin of stars

Some of the stars found in Mandakini are arranged in the form of beautiful figures. These shapes are called constellations / constellations. Like Saptarishi Mandal (Usrsa major great bear), Orion (Orion-great hunter), Cygnus-swan. Hydra, Hercules etc. According to the International Astronomical Union (IAU), there are a total of 88 constellations in the sky. * The largest constellation among these is Centaurus which has 94 stars. Hydra has at least 68 stars. At present, not only those stars in the constellation, but also the space around them is considered to be included, which contains dust and gas. * A group of seven bright stars visible in the sky towards the north in the northern hemisphere, whose shape is like a plough. In this, four stars form a trapezium, and the remaining three stars appear in the form of a curve.
Which are designated by the name of Great Bear. The front two stars of the quadrilateral are called indicators. The line joining these two stars passes through near the pole star. The Saptarshi Mandal appears to revolve around the pole star, but both the guide stars and the pole star are in a straight line in each position. Saptarshi Mandal is helpful for identifying the pole star at night.

Nakshatra (Star Group)

According to Vedic texts, a group of stars arranged in a certain shape is called Nakshatra.* There are about 27 constellations in the sky around the Earth which are visible in the night sky. Generally it is associated with the path of the moon. The Moon, while orbiting the Earth, passes one Nakshatra every day. In this way, the Moon passes through 27 star clusters ie Nakshatras while going round the Earth. Some Nakshatras are Megha, Swati, Chitra, Hasta, Vishakha, Anuradha, Jyestha, Rohini, Ashadh, Shravan, Ghanishtha, Kritika, Bharani, Purvabhadrapada, Uttara Bhadrapada, Ashlesha, Revati, Ardra, Punarvas etc.

Zodiac (Zodiac Cycle)

The Earth also passes through 12 star clusters during its orbit around the Sun. The sizes of these star clusters are different. They are called by different names according to their shape. The Nakshatra in the shape of a fish is called ‘Pisces’ and the Nakshatra in the shape of scales is called ‘Libra’. In Indian astrology, the above star groups i.e. Nakshatras are called zodiac. Like- Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Capricorn, Sagittarius, Aquarius and Pisces.

Orion Nebula

This is the region of the coolest and brightest stars in its galaxy ‘Mandakini’. It is about 1600 light years away from Earth. Its mass is believed to be equal to 700 solar masses. The nebula spans approximately 15 light years. The hot bright young stars revolving around it make the temperature around 10000°C and keep this region bright.

Boomerang Nebula

It is a young planetary nebula located approximately 5000 light-years away from Earth in the constellation Centaurus. Which is a glowing sphere of ionized gas emanating from a star like the Sun which is in the last stage of its life. According to astronomers the boomerang is expanding faster and using less energy in the process. Adiabatic expansion is taking place in it due to which cooling effect is being generated in it, the atmosphere around it is cooling down.



Quasars are a qusistaller radio sources, located at a distance of 4 to 10 billion light years. They emit light. Their information is obtained from the radio waves coming from them. Recent research has shown that quasars are actually the central part of a galaxy that we do not know about. There is a possibility of black hole in the center of quasars.


It is also called neutron star. In fact, it is a celestial body which emits radio waves at regular intervals in the form of vibrations. Radio waves are emitted every 1/30 second by the pulsars of the Crab Galaxy. It is hypothesized that pulsars are small objects – but larger than Earth. It is noteworthy that the mass of the pulsar is more than that of the Sun, the magnetic field is 20 trillion times more than the Earth’s magnetic field and the rotation speed is about 7000 km/s.

Pole Star

This is the position at the zenith of a person standing at the North Pole of the Earth. That is, its rays make an angle of 90° on the North Pole of the Earth. It is noteworthy that the latitude of the earth is determined on the basis of the angle of incidence of the rays of the pole star on the surface of the earth. This star is a member of the Ursa Minor or Little Bear star group, 700 light-years away from Earth. * This star can be seen at one place in the sky for 24 hours from any place in the Northern Hemisphere.
The pole star is also designated by the name of ‘Alpha Us Minoris’ according to the naming system of astronomy. It is a giant star of ‘F class’ (bright yellow) which is 2200 times more luminous than the Sun. In fact, the pole star is not alone but a pair of three stars, named Polaris ‘A’, Polaris ‘B’, and Polaris ‘P’ respectively. Of these, the one we can see with the naked eye is Polaris ‘A’, which is the main star of this group and its characteristics are shown above. Polaris ‘B’ is at a distance of 2400 astronomical units from the main star (the distance from the Earth to the Sun is called one astronomical unit and one light year is approximately equal to 63240 astronomical units), and it is able to revolve around the star Polaris ‘A’. Takes about 42000 years. Polaris ‘B’ was discovered by William Herschel in the year, 1780. In the year 1929, another dwarf star Polaris ‘P’ was discovered, which revolves around Polaris ‘A’ in 29.6 years, being at a distance of only 18.5 astronomical units. Polaris ‘P’ is also known as Polaris ‘A’ (short for ‘A’) or Polaris ‘AB’.

Baby Boom Galaxy

NASA scientists have announced the discovery of an amazing star-forming galaxy in the distant universe, which is far ahead of our own galaxy ‘Mandakini’ in star formation. Scientists have given it the noun of ‘baby boom galaxy’ or ‘rare machine for making stars’. It produces four thousand stars every year, while our Milky Way produces only 10 stars every year:
The ‘Baby Boom Galaxy’ belongs to the ‘Starburst Galaxy’, the most luminous and oldest group of galaxies. It is known that this galaxy forms almost all its stars at once.
NASA’s Hubble Space Telescope and Japan’s Subaru telescope on top of Hawaii’s Maunakei Hill first detected the ‘baby galaxy’ in the form of light images.

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