Space Science (A) Stars and Galaxies

Astronomy : It is the branch of science deals with study of celestial objects, space and universe

Star:1) It is a massive self luminous celestial object

2)It contain lot of gaseous matter held together by gravity.

3) It emits radiation through nuclear reactions

Eg: Sun , Sirius, Polaris , Arcturus

* Star nearest to earth is ------> Sun

(Distance = 1.5 X 108 Km )

● Stellar evolution is the process involved in the entire life cycle of Stars from birth to death

Stellar evolution

How a star is Born :(Sun like Star )

Step 1: Protostar : ● Huge gaseous

hydrogen contracts under its own gravity

● Density and temperature increases at center

● Formation of spherical structure at centre

● This is called protostar

Step II : Steady state

● Hydrogen nuclei fuse to form Helium nuclei● Temperature increases and lot of energy is released ● Due to enormous release of energy matter is expanded

away from center● Force of gravity tries to contract matter but radiation

pressure tends to expand matter ● Two opposing forces balance each other ● Now star attains steady state.

● Red Giant is the stage in the life cycle of star when core consists of helium and star become huge in size due to expansion and hence become red in colour

● Eg: Betelgeuse – a star in the constellation Orion , is a red Giant

How is Red Giant Formed? ● Helium core began to contract under

gravity● Hydrogen fuel at core get exhausted and

fusion stops in core ● There is increase in temperature● Hydrogen left in peripheral region start

fusion reaction causing outer layer to expand

● Star become gigantic in size● This cools the star and its colour

changes to red

Step III: Red Giant Star

Planetary Nebula● The shell of glowing

gaseous matter surrouding an evolved star from which it is ejected into space due to outward pull of radiation is called planetary nebula

● Sun like stars usually shed their outer shell towards the end of their red giant stage

● The material ejected fro the star has similarity with that of planet and hence the name

Chandrashekar’s Limit ● What happens to a star after

Red giant Stage depends on its initial mass

● Here the critical value is about 1.4 times the solar mass .

● This value is known as chandrashekar’s limit

● Star with mass lower than chandrashekar’s limit will end up as ------> White dwarf

● Star with mass higher than chandrashekar’s limit will Undergo a ------> Supernova explosion

Step IV : White Dwarf (Mass less than 1.4 Chandrashekhar’s Limit)

● A helium star that is dense , small and bright is called white dwarf.● Star of mass less than 1.4 times the solar mass evolve into white dwarf stage

How is White dwarf formed?● As the core of red giant contracts temperature reaches 108 Kelvin ● Helium fuses to form Carbon ● Once entire Helium fuses into carbon the core cannot contract ● Outer envelope get detached and thrown into space ● Star collapse under the gravity ● Due to increase in temperature Star shines and now called White Dwarf

Step V : Black Dwarf ● After White dwarf stage

nuclear reaction inside the star stops

● Internal energy is lost ● NO light is emitted● Star become Black

dwarf that is the death of star

Death of Sun like Star

Stages of stellar Evolution Sun like Star 5 times as sun 30 times as sun

1. Protostar 1. Protostar 1. Protostar

2.Steady State 2.Steady State 2.Steady State

3.Red Giant 3.Red Giant 3.Red Giant

4.White Dwarf 4. Supernova 4. Supernova

5.Black DWarf 5.Neutron Star 5.Black Hole

Supernova ● After red giant if the mass of star is about 5

times that of sun then supernova explosion takes place

● Helium formed in the core continue to contract under gravity.

● Due to increase in the temperature helium fuses into Carbon -----this followed by fusion of carbon into Oxygen

● The process continues and ther is formation of heavier elements such as Magnesium and silicon core which lie one inside other

● Huge amount of energy is produced ● This result in increase in temperature and

pressure● Star explode with brilliant flash ● Matter is thrown into the space with high

speed

● This is called supernova

● After Supernova a sphere of neutron remains at center and is called neutron star.

● It is highly dense object.● It collapse under the

influence of its own gravity

● It is a star composing mainly of packed neutrons

● It is the super dense remnant of supernova

Neutron Star

Black Hole● Black hole takes place if

the mass of star is 30 times that of the mass of sun

● Black hole are formed from a massive neutron star that go on contracting infinitely under the influence of their own gravity

● Black hole are so massive and dense that even light cannot escape from them.

Properties of Black hole cannot be determined

● Nothing comes out of black hole

● No information in the form of light or radio waves comes from a black hole.

● This is why it is not possible to determine temperature , pressure or chemical composition of a black hole.

Special stars Pulsar : a spinning neutron star that emmits radio wave is called Pulsar.

Quasar : ● It is massive and remote

celestial object● Emits large amount of

energy● It has Star – like image in

telescope● Quasar is the short form

of Quasi Stellar Sources

● The Stars differ in their temperature.● The different colour of the star are due to

difference in their temperatureStar Name Colour Surface temperature

Betelgeuse ( Red Star in the night Sky)

Red 2500 – 3500 K

Arcturus Orange yellow 3500 – 5000 K

Sun Yellow 5000 – 6000 K

Sirius ( Brighest star in the sky )

Yellowish white 6000 – 10000 K

Rigel Bluish White 10000 - 50000 K

Why do star differ in their Colour

Betelgeuse ( Red Star in the night Sky) Arcturus

Sun Sirius ( Brighest star in the sky ) Rigel

Galaxy A group of star containing thousand of million of stars along with gas and dust held together by the force of gravity orbiting about a common center is called Galaxy.

Milky way: ( Spiral Galaxy)● It is the galaxy which includes the

sun and solar system.● The diameter of galaxy is about

1,00,000 light years● It looks like Flat Disc with a central

bulge and thickness tapers towards edge

● Sun is located in the galaxy about 28,000 light years from the center

Different types of Galaxies

1.Elliptical Galaxies :● These are most common

type of galaxies in the universe

● They contain quite dim stars

● It is difficult to see the stars of galaxy

Spiral galaxy

● They have spiral shape .

● They contain very bright and newly formed stars.

● Our galaxy milky way is a spiral galaxy

Irregular Galaxy

● These galaxies do not have shape

● These galaxies are normally small and faint

● Hence more difficult to detect

Cosmology ● The study of the universe as a whole, including

theories about its origin , evolution, structure and future is called Cosmology

● The most accepted theory about origin of universe is ------ Big Bang Theory

Big Bang Theory● Big bang theory was put forward by

Edwin Hubble.● According to this theory the matter

in the universe was in the form of fiery region forming a huge dens primordial mass known as primordial fire ball

● It had high density and temperature● Due to increase in the pressure and

temperature it was exploded about 15-20 billions years ago

● This explosion is called big bang● This explosion threw matter and

radiation in space with high speed ● This caused universe to expand ● As the matter and radiation cooled ,

stars and galaxies were formed

Red Shift ● Long observation of the spectra of

galaxies reveals a gradual shift of the spectral lines towards longer wavelength. This shift is known as ‘RED SHIFT’ of galaxies.

● Edwin Hubble and his co-workers studied the red shift of various galaxies .

● They discovered that red shift of galaxy is proportional to its distance from us.

Hubbles Law“ The velocity of recession of a

celestial body is proportional to its distance from observer’’

➢ The star nearest to earth is _____➢ The sun is currently in ______stage➢ The nuclear fuel that is currently used up in the sun is _______➢ The colour of Betelgeuse is_____

the densest celestial object in the universe is _____➢ The galaxy of which we are part is _____➢ The Indian name of Milky way is ______➢ The diameter of milky way is _____ light years ➢ The theory that explains the origin of universe satisfactorily is

____➢ The sun will eventually ends up as ______➢ The spinning neutron star is called ______➢ A pulsar emits ______ waves ➢ Light year is a unit of ____________

Evaluation

Thank YouPrepared by

Gulzar . I . DGovernment P.U.college

(High School)ThyamagondluNelamangala tq

Bangalore rural distMob no : 8277367100