Chapter-24
Space Science
A.Stars and Galaxies
Learning Card-1
Choose the correct answer:
1. The element which was condensed to form a protostar is.
a. Hydrogen b.Helium c. Lithium d. Carbon.
2. The value of chandrashekar limit is
a) 1.4 times the earth mass
b) 1.4 times the sun mass
c) 14 times the earth mass
d) 14 times the sum mass
3. The celestial object emitting radiation in pulses is called
a. Quasar b. Black hole c. white dwarf d. Pulsar.
4. The period of revolution of the Sun in the Milky Way galaxy is
a. about 250 years
b. about 250 million light years.
c. about 100 years
d. about 25 million years.
5. The theory which explains about the begining of the universe is
a. Supernova theory b. steady state theory
c. Bigbang theory d. Antiuniverse theory
Question and Answers:
1. Which is the first stage in the evolution of stars?
Protostar
2. What is planetary nebulla?
The outer envelope of the Red gaint gets detached and thrown out into space. It forms a cloud called Planetary Nebula
3. Define pulsars.
The neutron star which emits radiation in pulses are called Pulsars
4. What is supernova explosion?
The explosion of stars which are 5 times more massive than sun, after Red gaint state is called Supernova explosion
5. Name the types of galaxies.
a. Elliptical galaxies.
b. Spiral galaxies
c. Irregular galaxies.
6. Write an exmple for spiral galaxy.
Milky way or Akasha ganga
7. Name the theory that explains about the origin of universe.
Big bang theory.
8. What is big bang?
The explosion of Primordial Fire ball with a bang which led to the beginning of universe is called “Big bang”
Chapter-24
Space Science
A.Stars and Galaxies
Learning Card-2
Choose the correct answer:
1. The evidence for the universal expansion is
(a) Doppler effect of light (b) Doppler effect of sound
(b) Existance of black hole (d) Existance of solar system
2. A star to end its life as white dwarf its mass after redgaint stage must be
(a) Equal to Chandrashekar limit
(b) Greater to Chandrashekar limit
(c) Lesser to Chandrashekar limit
(d) 1.4 times lesser to its original mass
3. The stages of evolution of stars
(a) Protostar --> Red giant--> White dwarf--> Steady state
(b) Protostar--> Neutron star--> Red gaint--> Black hole
(c) Protostar--> Steady state--> Red gaint--> Neutron star
(d) Protostar--> Steady state--> White dwarf--> Neutron star
Question and Answers:
1. What is galaxy?
Galaxy is a group of billions of stars, gas, and dust which are bound by huge gravitation force.
2. State Hubble's law.
Hubble's law - "The velocity of the recession of a celestial body is proportional to its distance from us".
3. Name our native galaxy.
Milky Way or Akasha Ganga
4. A star observed to be bluish white in colour. What is the approximate temperature on its surface?
About 10,000K - 50,000K
5. Write the differences between
(a) Pulsars and Quasars
| Pulsars | Quasars |
| It is a fast spinning neutron star | Group of stellar objects, emitting radiation |
| Emits radiation in pulses | They emit more of radio waves |
(b) Neutron star and black hole
| Neutron star | Black hole |
| Emits radiation | Does not emit radiation |
| Possible to identify in space | Not possible to identity in space |
6. Super match
| Temp | Colour | Star |
| 2000-3500K | Red | Betelgeause |
| 3500-5000K | Orange yellow | Arcturus |
| 5000-6000K | Yellow | Sun |
| 6000-10,000K | Yellowish white | Sirius |
| 10000-50000K | Bluish white | Rigel |
7. Write a short note on Milky Way.
Milky Way galaxy is our native galaxy, where our solar system is present. It is a spiral galaxy. It consists of about 200 billion stars in it. Its diameter is about 1 lakh light year. Its diameter is about 1 lakh light year. Its central thickness is about 6000 light year. Sun is located about 28000 light years from the centre.
8. What is stellar evolution?
The process from bisth to the death of star is called stellar evolution.
9. Write the different stages of evolution of star having the mass lesser than the Chandrashekar limit.
Protostar-->Steady state--> Red gaint stage -->White dwarf
10. Write the different stages of evolution of a star having the mass greater than the Chandrashekar limit.
(a) 5 times greater mass them sun
Protostar --> Steady state -->Red gaint -->Neutron
(b) 30 times greater mass than sun
Protostar -->Steady state -->Red gaint--> Neutronstar -->Blackhole
11. Explain the changes that occur in a star to reach its steady state.
Huge hydrogen gas clouds are contracted due to gravity
– Increase in density and pressure
– Spherical mass formed at the centre
– 99% mass concentrated at centre – protostar
– Huge ball contracts due to gravitation
– Temperature increases to millions of Kelvin
– Hydrogen fuses to form helium, heat, and light radiation are emitted
– Outward force due to radiation expands star
– Outward force balances inward gravitational pull--> steady state
12. Write the changes that occur in the star before it reaches the red gaint stage.
After steady state - outward radiation force increase – Outer layer expands - surface area increases – Temperature decreases - emits radiation of lesser frequences - appearses red in colour
Chapter-24
Space Science
A.Stars and Galaxies
Learning Card-3
Choose the correct answer:
1. Which is the fundamental force led to the birth of star.
a) Electrostatic force b) Nuclear force
c) Gravitational force d) Magnetic force
2. The event that occurs when iron forms in the core of a star is.
a) Big bang b) Supernover explosion c) Neutron star d) Pulsar
3. Heavy mass, small volume, intense gravition field are the features of
a) Quabars b) Pulsar c) Whitedwarf d) Blackhole
Question and Answers:
4. A and B are two galaxies. If A is showing red shift and “B” is showing blue shift, how do you interprete their motion related with earth?
Star A is moving away from the earth and star B is moving towards the earth
5. Comment on the existance of life on earth, when sun reaches red gaint stage.
The tempeature on the earth surface increases. The atmosphere may, blown off. The oceans may go dry. Due to higher temperature the life on the earth may be destroyed (vanished)
6. You are an astronomer. How do you find the existance of the black hole in the universe?
Black hole cannot be detected by the properties like pressure or temperature. It could be detected only by its high gravitation force. It does not allow even the light to come out of it. It can grab or swallow the near by objects.
7. Why a star becomes red in red-gaint stage.
In the red gaint stage the star begans to swell and the surface area of the star increases.As a result temperature of the star decreases and hence it emits light of lower frequency. There fore star appears to be Red in clour
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