Maharashtra Board Class 8 Science Chapter 19 Life Cycle of Stars Solutions

1. Search And You Will Find:

Question a. Our galaxy is called .......... .
Answer: Our galaxy is called the Milky Way and Mandakini.
In simple words: Our galaxy is known by two main names: the Milky Way and Mandakini.

🎯 Exam Tip: Remember both names for our home galaxy, as they are often interchangeably used in questions.

Question b. For measuring large distances, ........ is used as a unit.
Answer: For measuring large distances, the light year is used as a unit.
In simple words: A light-year is a unit of distance, representing how far light travels in one year, used for vast cosmic distances.

🎯 Exam Tip: Understand that a light-year measures distance, not time, a common misconception.

Question c. The speed of light is ............. km/s.
Answer: The speed of light is 300000 km/s.
In simple words: Light travels incredibly fast, covering 300,000 kilometers every second.

🎯 Exam Tip: Memorize the speed of light as a fundamental constant in physics and astronomy.

Question d. There are about .......... stars in our galaxy.
Answer: There are about 100 billion stars in our galaxy.
In simple words: Our galaxy, the Milky Way, contains an estimated 100 billion stars.

🎯 Exam Tip: This figure helps to appreciate the vast scale of our galaxy; specific numbers for astronomical objects are often tested.

Question e. The end stage of the Sun will be .......... .
Answer: The end stage of the Sun will be a white dwarf.
In simple words: After exhausting its nuclear fuel, our Sun will eventually shrink and become a white dwarf.

🎯 Exam Tip: Know the life cycle stages of stars, especially for average-mass stars like our Sun, as this is a core concept.

Question f. Stars are born out of ............ clouds.
Answer: Stars are born out of interstellar clouds.
In simple words: Stars form when dense regions within vast clouds of gas and dust between stars collapse under gravity.

🎯 Exam Tip: The term "interstellar clouds" is key to describing the birthplaces of stars; ensure correct terminology.

Question g. Milky way is a .......... galaxy.
Answer: Milky way is a spiral galaxy.
In simple words: Our home galaxy, the Milky Way, has a characteristic spiral shape with arms extending from its center.

🎯 Exam Tip: Classify galaxies by their shapes (spiral, elliptical, irregular) and know which type the Milky Way is.

Question h. Stars are gigantic spheres of .......... gas.
Answer: Stars are gigantic spheres of hot gas.
In simple words: Stars are massive balls of extremely hot, glowing gas, primarily hydrogen and helium.

🎯 Exam Tip: Emphasize "hot gas" to convey the primary composition and state of matter in stars.

Question i. The masses of other stars are measured relative to the mass of the .......... .
Answer: The masses of other stars are measured relative to the mass of the Sun.
In simple words: The Sun's mass serves as a standard unit for comparing the masses of other stars in astronomy.

🎯 Exam Tip: Understanding this relative measurement helps in comprehending stellar classifications and evolution.

Question j. Light takes .......... to reach us from the Sun while it takes .......... to reach us from the moon.
Answer: Light takes about 8 minutes to reach us from the Sun while it takes about 1 second to reach us from the moon.
In simple words: Sunlight reaches Earth in approximately 8 minutes, while moonlight (reflected sunlight) takes only about 1 second to travel from the Moon to Earth.

🎯 Exam Tip: These timeframes illustrate the vast difference in distance between the Earth-Sun and Earth-Moon systems.

Question k. The larger the mass of a star, the faster is its .......... .
Answer: The larger the mass of a star, the faster is its evolution.
In simple words: More massive stars burn through their nuclear fuel at a much higher rate, causing them to evolve and reach their end stages more quickly than less massive stars.

🎯 Exam Tip: This is a crucial concept linking a star's mass directly to its lifespan and evolutionary speed; understand the inverse relationship.

Question l. The number of fuels used in the life of a star depends on its .......... .
Answer: The number of fuels used in the life of a star depends on its mass.
In simple words: A star's initial mass determines how many different types of nuclear fusion reactions it can sustain throughout its lifetime, influencing its evolution.

🎯 Exam Tip: Recognize mass as a primary factor influencing a star's entire life cycle, including its fuel consumption and end stage.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक सर्पिल आकाशगंगा को दर्शाता है, जिसमें हमारा सौर मंडल भी स्थित है। यह आकाशगंगा तारों, गैस और धूल का एक बड़ा संग्रह है।

2. Who Is Telling Lies?

Question a. Light year is used to measure time.
Answer: False. (Light year is used to measure distance.)
In simple words: The statement is false because a light-year is a unit of astronomical distance, not time.

🎯 Exam Tip: Always remember that a light-year is a unit of distance (how far light travels in a year), not a unit of time.

Question b. End stage of a star depends on its initial mass.
Answer: True.
In simple words: The ultimate fate of a star, such as becoming a white dwarf, neutron star, or black hole, is directly determined by its starting mass.

🎯 Exam Tip: A star's initial mass is the most critical factor influencing its entire life cycle and final form; this is a fundamental concept.

Question c. A star ends its life as a neutron star when the pressure of its electrons balances its gravity.
Answer: False. (A star ends its life as a neutron star when the pressure of its neutrons balances its gravity.)
In simple words: The statement is false; in a neutron star, it is the degeneracy pressure of neutrons, not electrons, that counteracts gravity.

🎯 Exam Tip: Distinguish between electron degeneracy pressure (in white dwarfs) and neutron degeneracy pressure (in neutron stars) as the stabilizing forces.

Question d. Only light can emit from the black hole.
Answer: False. (Not even light can be emitted by a black hole.)
In simple words: This statement is false because a black hole's immense gravitational pull prevents anything, including light, from escaping once it crosses the event horizon.

🎯 Exam Tip: A defining characteristic of a black hole is its ability to trap light, making it truly "black."

Question e. The Sun will pass through the supergiant stage during its evolution.
Answer: False. (The Sun will pass through the red giant stage during its evolution.)
In simple words: This is false; our Sun is not massive enough to become a supergiant star and will instead evolve into a red giant, then a white dwarf.

🎯 Exam Tip: Differentiate between the evolutionary paths of average-mass stars (like the Sun) and massive stars; only massive stars become supergiants.

Question f. The Sun will end its life as a white dwarf.
Answer: True.
In simple words: The Sun, being an average-mass star, is predicted to eventually shed its outer layers and leave behind a dense core, a white dwarf.

🎯 Exam Tip: Understand the final stages for Sun-like stars; white dwarfs are the common end-state for stars up to about 8 solar masses.

3. Answer The Following Question:

Question a. How do stars form?
Answer: There are huge clouds of gas and dust in the empty spaces between the stars in a galaxy. These clouds are called interstellar clouds. The size of an interstellar cloud is about a few light years.
When an interstellar cloud starts contracting due to some disturbance, its density and temperature increase. This results in formation of a dense sphere of hot gas and nuclear energy generation starts at the centre of the star. Therefore, the gas sphere becomes self-luminous. Thus a star is formed, i.e., a star is born.
A huge interstellar cloud can produce thousands of stars at a time.
In simple words: Stars are born from massive interstellar clouds of gas and dust that collapse under gravity. As the cloud contracts, it heats up, forming a dense sphere where nuclear fusion begins, making it a self-luminous star.

🎯 Exam Tip: Focus on the role of gravity and nuclear fusion as the key mechanisms for star formation from interstellar clouds.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह हबल अंतरिक्ष दूरबीन द्वारा ली गई अंतरतारकीय बादलों की एक तस्वीर है, जहाँ से नए तारों का जन्म होता है। ये बादल गैस और धूल से बने होते हैं।
ℹ️ चित्र व्याख्या (Diagram Explanation): यह तारों का एक बड़ा समूह दर्शाता है। इनमें से अधिकांश तारे एक ही अंतरतारकीय बादल से बने हैं, जो तारों के निर्माण की प्रक्रिया को दर्शाता है।

Question b. Why do stars evolve?
Answer: Although stars appear stable for quite a long period of time, their properties do change, though very slowly. A change in the properties of a star, leading to its passing through different stages, is called evolution of the star. Burning of the fuel at the centre of the star and a gradual decrease in its amount is the main reason of evolution of a star.
In simple words: Stars evolve because they continuously consume their nuclear fuel, primarily hydrogen, in their core. As this fuel depletes, the star's internal balance changes, causing its properties to alter and leading it through different life stages.

🎯 Exam Tip: The depletion of nuclear fuel and the subsequent changes in internal pressure and temperature are the fundamental drivers of stellar evolution.

Question c. What are the three end stages of stars?
Answer:
1. Stars having initial mass less than 8 times the mass of the Sun ultimately become white dwarfs.
2. Stars having initial mass between 8 and 25 times the mass of the Sun ultimately become neutron stars.
3. Stars having initial mass larger than 25 times the mass of the Sun ultimately turn into black holes.
In simple words: The final stage of a star's life depends on its initial mass: less massive stars become white dwarfs, medium-mass stars become neutron stars, and very massive stars become black holes.

🎯 Exam Tip: Clearly remember the mass thresholds for each of the three end stages of stars, relating them to solar mass units.

Question d. Why was the name black hole given?
Answer: When a star having initial mass larger than 25 times the mass of the Sun reaches its end stage, its gravitational force and density increase exponentially. All nearby objects get attracted towards the star and nothing can come out of it, not even light. All incident light is absorbed by the star. We can probably see a very minute black hole at its place. Hence, the name is given as black hole.
In simple words: The name "black hole" is given because its gravitational pull is so extreme that nothing, not even light, can escape from it, making it appear completely black to an observer.

🎯 Exam Tip: The defining characteristic of a black hole is its event horizon, beyond which the escape velocity exceeds the speed of light, trapping everything inside.

Question e. Which types of stars end their life as a neutron star?
Answer: Stars having initial mass between 8 and 25 times the mass of the Sun end up as neutron stars. When these stars pass through the supergiant stage, their size increases to 1000 times. Huge explosion that occurs in the last stage of these stars is very powerful and very high energy is given off. After the huge explosion, called the supernova explosion, their central portion contracts in size to about 10 km. In this stage, such stars are completely made up of neutrons and hence are called neutron stars.
In simple words: Stars with an initial mass between 8 and 25 times that of the Sun will end their lives as neutron stars, forming after a supernova explosion compresses their core into a dense ball of neutrons.

🎯 Exam Tip: Associate neutron stars with massive progenitors (8-25 solar masses) and the supernova explosion that precedes their formation.

4. A. If You Are The Sun, Write About Your Properties In Your Own Words.

Question A. If you are the Sun, write about your properties in your own words.
Answer: There are billions of stars in the galaxy called the Milky Way and Mandakini. I am one of the small stars called the Sun. I have my own family called the solar system. There are planets, satellites, asteroids, comets and meteors in my family. My mass is \(2 \times 10^{30}\) kg which is about 3.3 lakh times that of the earth. With a radius of 695700 km, my size is about 100 times that of the earth. My surface temperature is about 5800 K while it is \(1.5 \times 10^7\) K at the centre.
72% of my mass consists of hydrogen while 26 % consists of helium. Rest 2 % is made up of elements heavier than helium. I am about 4.5 billion years old and the scientists on the earth have concluded that not much change has taken place in my properties during this period. According to the scientists, in the end stage of my life, I will turn into a red giant star. Thereafter, I will first explode and then contract to become as small as the earth. I will appear small as well as white and hence, I will be called a white dwarf. This will be my last stage for ever.
In simple words: The Sun describes itself as an average star in the Milky Way, the center of the solar system, with a mass of \(2 \times 10^{30}\) kg, a radius 100 times Earth's, and surface temperature of 5800 K. Composed mostly of hydrogen and helium, it's 4.5 billion years old and is projected to become a red giant, then a white dwarf.

🎯 Exam Tip: When describing the Sun, include its key physical properties (mass, size, temperature, composition) and its predicted evolutionary path (red giant to white dwarf).

B. Describe White Dwarfs.

Question B. Describe white dwarfs.
Answer: Depending on the initial mass, stars can reach one of the three end stages. White dwarf is one such stage of stars having initial mass less than 8 times the mass of the Sun. These stars undergo huge expansion and their radius increases by a factor of 100 to 200. These stars appear reddish because of their large size and lower temperature. Hence, these stars are also called red giant stars.
At the end of their evolution, these stars explode, their outer gas envelope is thrown outward and the inner part contracts to the size of the earth. However, the density in the star becomes very high. In this stage, the pressure due to electrons becomes independent of temperature and sufficient to balance the gravitational force for ever.
In this stage, such stars look white and due to their small size they are called white dwarfs.
In simple words: White dwarfs are the dense, small, and hot remnants of stars with an initial mass less than 8 times the Sun's. They form after a star sheds its outer layers and its core contracts to about Earth's size, stabilized by electron degeneracy pressure.

🎯 Exam Tip: Highlight the defining characteristics of white dwarfs: small size (Earth-like), high density, stability due to electron degeneracy pressure, and their origin from Sun-like stars.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक सफेद बौने तारे के निर्माण के दौरान बाहर फेंके गए बाहरी गैसीय आवरण को दर्शाता है, जिसके केंद्र में सफेद बौना तारा होता है।

Can You Recall?

Question 1. What is a galaxy?
Answer: A system of billions of stars, their planetary systems and interstellar clouds of gas and dust held together by gravitational attraction is called a galaxy.
In simple words: A galaxy is a massive system of billions of stars, planetary systems, gas, and dust, all bound together by gravity.

🎯 Exam Tip: Remember that gravity is the primary force that holds a galaxy's vast components together.

Question 2. What are the different constituents of our solar system?
Answer: The different constituents of our solar system are as follows :
1. Sun as a star.
2. Eight planets, namely, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune; of which Mercury, Venus, Earth and Mars are made up of rocks and minerals, while Jupiter, Saturn, Uranus and Neptune are made up of gases.
3. Natural satellites of some planets revolving around the respective planets.
4. Asteroids located between Mars and Jupiter.
5. Comets made up of ice, dust and gases.
6. Meteors and meteoroids.
In simple words: Our solar system consists of the Sun, eight planets (both rocky and gas giants), their natural satellites, asteroids, comets, and meteors, all gravitationally bound.

🎯 Exam Tip: List the major components of the solar system, including the star, planets, and minor bodies, demonstrating a comprehensive understanding.

Question 3. What are the major differences between a star and a planet?
Answer:
1. Nuclear/atomic explosions regularly take place at the centre of stars. This causes the discharge of heat and light. Hence, stars shine. Planets do not discharge any light. They are visible due to the light reflected by them.
2. Stars are very big in size and massive relative to planets.
3. Stars twinkle, planets do not.
4. Stars are made up of hydrogen, helium and other light elements.
5. Planets are made up of solid, liquid or gaseous substances or a combination thereof.
In simple words: Stars generate their own light and heat through nuclear fusion, are much larger, and twinkle; planets, on the other hand, reflect light, are smaller, and do not twinkle, being composed of rock, liquid, or gas.

🎯 Exam Tip: Focus on the ability to perform nuclear fusion as the key distinguishing factor, along with size, luminosity, and composition differences.

Question 4. What is a satellite?
Answer: An astronomical object orbiting a planet is called a satellite.
In simple words: A satellite is any celestial body that orbits around a larger planet.

🎯 Exam Tip: Define a satellite simply as an object in orbit around a planet, whether natural (like the Moon) or artificial.

Question 5. Which is the star nearest to us?
Answer: The star nearest to us is the Sun.
In simple words: The Sun is the star closest to Earth.

🎯 Exam Tip: This is a direct factual recall question; ensure accurate identification of the Sun as our nearest star.

Project:

Question 1. Use your imagination and make models of the Milky Way and the solar system.
Answer: N.B. Students can make these models and display the same in science exhibition. You can use sand, scrap material, stones, pebbles, marbles, pieces of glass, beads, etc.
In simple words: This is a creative project encouraging students to build physical models of the Milky Way galaxy and our solar system using various craft materials.

🎯 Exam Tip: For practical-based questions, describe the components and materials clearly to show understanding of the required outcome.

Question 2. Write the effects: If the Sun disappears ..........
Answer: N.B. You can write the effects with the help of the following points:
1. No sunrise, no sunset, no beauty of morning and evening wee hours.
2. In the absence of the gravitational force due to the Sun, the earth will drift away in the galaxy.
3. Darkness, no source of energy, end of life on the earth.
4. Moon will be invisible.
5. The temperature of the earth will fall below the freezing point of water. All oceans will also freeze.
6. Even the atmosphere will freeze and fall on the earth. This will cause more cosmic rays to reach the earth.
In simple words: If the Sun disappeared, Earth would experience perpetual darkness, plummeting temperatures causing oceans and atmosphere to freeze, a loss of solar gravity leading to drifting, and an increase in harmful cosmic radiation, effectively ending all life.

🎯 Exam Tip: When outlining hypothetical scenarios, consider the cascading effects across multiple scientific domains (gravity, light, temperature, life, atmosphere).

Class 8 Science Chapter 19 Life Cycle Of Stars Important Questions And Answers

Match The Columns:

Question 1.

Column 'A'	Column 'B'
1. Gravitational force	a. Alpha Centauri
2. The star nearest to us other than the Sun	b. \(2 \times 10^{30}\) kg
3. Mass of the Sun	c. \(10^{30}\) g
	d. towards the centre of a star or a planet

Answer:

Column 'A'	Column 'B'
1. Gravitational force	d. towards the centre of a star or a planet
2. The star nearest to us other than the Sun	a. Alpha Centauri
3. Mass of the Sun	b. \(2 \times 10^{30}\) kg

In simple words: This table matches astronomical terms like gravitational force, the nearest star other than the Sun, and the Sun's mass with their correct descriptions or values.

🎯 Exam Tip: Pay close attention to numerical values and specific definitions when matching columns for accuracy.

Question 2. Mass of the star:

Column 'A'	Column 'B'
1. < 8 Msun	a. Proton star
2. between 8 and 25 times Msun	b. Black hole
3. > 25 Msun	c. Neutron star
	d. White dwarf

Answer:

Column 'A'	Column 'B'
1. < 8 Msun	d. White dwarf
2. between 8 and 25 times Msun	c. Neutron star
3. > 25 Msun	b. Black hole

In simple words: This table correctly matches a star's initial mass range (relative to the Sun's mass) with its corresponding end stage.

🎯 Exam Tip: Memorize the critical mass thresholds that determine whether a star will become a white dwarf, neutron star, or black hole.

Answer The Following Questions In One Sentence Each:

Question 1. Name the star nearest to the earth.
Answer: The Sun.
In simple words: The Sun is our nearest star.

🎯 Exam Tip: This is a direct knowledge recall; ensure you can instantly identify the Sun as Earth's closest star.

Question 2. Other than the Sun, which is the star nearest to the earth?
Answer: Alpha Centauri.
In simple words: Alpha Centauri is the closest star system to Earth, besides our Sun.

🎯 Exam Tip: Be precise: Alpha Centauri is a star system, and its closest component (Proxima Centauri) is the absolute nearest non-solar star.

Question 3. What would be the last stage of the Sun?
Answer: The last stage of the Sun would be white dwarf.
In simple words: The Sun's ultimate fate is to become a white dwarf.

🎯 Exam Tip: Reinforce the understanding of the Sun's specific evolutionary path as an average-mass star.

Question 4. Name two forces that act on any star.
Answer: Gravitational force and the force due to the pressure of hot gas are the two forces that act on any star.
In simple words: The two primary forces acting on a star are its inward gravitational pull and the outward pressure from its hot gas.

🎯 Exam Tip: Understand the concept of hydrostatic equilibrium, where these two forces balance to maintain a star's stability.

Question 5. What is a black hole?
Answer: A black hole is the end stage of a quite big star, where due to the extremely high gravitational force, nothing, not even light, comes out.
In simple words: A black hole is the collapsed remnant of a very massive star, possessing such strong gravity that nothing, not even light, can escape its pull.

🎯 Exam Tip: The key defining feature of a black hole is its immense gravitational force which prevents the escape of light.

Answer The Following Questions:

Question 1. How is stability of stars maintained?
Answer: Properties of a star remain unchanged for quite a long time. The gravitational force and the force due to the pressure of the hot gas act together on a star. The gravitational force acts towards the centre of the star and tries to bring the gas particles close together. Hot gas shows the tendency to spread and its force acts away from the centre of the star. This force tries to disperse the gas particles. A balance between the gravitational force and the force due to the hot gas keeps the star stable.
However, if the magnitude of any one force is more than that of the other force, the star either contracts or expands depending upon which force dominates.
In simple words: The stability of a star is maintained by a delicate balance between two opposing forces: the inward pull of gravity, which tries to collapse the star, and the outward pressure generated by the hot gas from nuclear fusion in its core, which tries to expand it. This equilibrium keeps the star stable for billions of years.

🎯 Exam Tip: The concept of "hydrostatic equilibrium" is central to explaining stellar stability; identify the two opposing forces and their balance.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक तारे में कार्यरत दो मुख्य बलों - गुरुत्वाकर्षण बल (अंदर की ओर) और गर्म गैस के दबाव के कारण उत्पन्न बल (बाहर की ओर) को दर्शाता है। इन बलों का संतुलन तारे को स्थिर रखता है।

 

causes the gas pressure to decrease and the balance between the gravitational force and the force due to the gas pressure is no more maintained.

As the magnitude of the gravitational force is now more than that of the force due to the gas pressure, the star starts contracting. This causes another fuel to start burning, e.g. on exhausting hydrogen, helium starts undergoing fusion. Availability of multiple fuels depends on the mass of the star.

The higher the mass of the star, the more is the number of fuels used. The star either contracts or expands during the course of using these fuels. This may cause the imbalance between the gravitational force and the force due to the hot gas.

3. Total exhaustion of the fuel: When all fuels are exhausted, the energy generation in the star finally stops completely and the temperature of the star starts decreasing. The balance between the gravitational force and the force due to the gas pressure can no more be maintained. The evolution of the star ends and the star proceeds to its end stage.

4. End stage of a star: Once the fuel in the star is totally exhausted, the energy generation in the star stops and subsequently the gas pressure decreases, the star starts contracting and its density starts increasing. When the density becomes very high, some new types of pressures are generated which are independent of the temperature of the gas.

In such a case, the pressure remains stable despite low temperature and absence of any energy generation and thus the star remains stable for ever. This stage is the end stage of the star. Depending on the initial mass, stars can reach one of the three end stages.

(i) Stars having initial mass less than 8 times the mass of the Sun ultimately become white dwarfs.
(ii) Stars having initial mass between 8 and 25 times the mass of the Sun ultimately become neutron stars.
(iii) Stars having initial mass larger than 25 times the mass of the Sun ultimately turn into black holes.
In simple words: Stars evolve through stages due to fuel burning and gravitational forces. Their life ends as white dwarfs, neutron stars, or black holes, depending on their initial mass.

🎯 Exam Tip: Understanding the four key stages of stellar evolution (initial stability, fuel burning, total exhaustion, and end stage) is crucial for describing a star's lifecycle.

Write Short Notes On The Following:

 

Question 1. End stages of stars having initial mass less than 8 times the mass of the Sun.
Answer: These stars undergo huge expansion and their radius increases by a factor of 100 to 200 during their various stages of evolution. These stars appear reddish due to their lower temperature. Hence, they are called red giant stars.

At the end of evolution, these stars explode, their outer gas envelope is thrown out and the inner part contracts roughly to the size of the earth. Hence, the density of the star becomes very high. In this stage, the pressure due to electrons becomes independent of temperature and sufficient to balance the gravitational force for ever. Such stars look white and due to their small size they are called white dwarfs.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र विभिन्न तारों के आकारों की तुलना दर्शाता है। इसमें सूर्य (Sun) और सुपर जायंट स्टार (Super Giant Star) के साथ-साथ सफेद बौने (White Dwarf) और लाल दानव तारे (Red Giant Star) के सापेक्ष आकार को दर्शाया गया है, जिससे छात्रों को उनके द्रव्यमान और तापमान के आधार पर तारों के विकास की कल्पना करने में मदद मिलती है।
In simple words: Stars with initial mass less than 8 times the Sun's mass become red giants, expanding and cooling, then shed their outer layers and contract into dense, hot white dwarfs.

🎯 Exam Tip: Remember that stars with less than 8 solar masses primarily evolve through a red giant phase before becoming white dwarfs, which are very dense and small remnants.

 

Question 2. End stage of the stars having mass between 8 and 25 times the mass of the Sun.
Answer: These stars pass through the red giant stage and later super giant stage, during which their size may increase to 1000 times. The huge explosion, called the supernova explosion, occurs in the last stage of the evolution. It is very powerful and very high energy is given off in this case.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक सुपरनोवा विस्फोट को दर्शाता है, जो तारों के जीवन चक्र के अंतिम चरणों में से एक है। यह एक विशाल तारकीय विस्फोट है जिसके दौरान एक तारा अपने पदार्थ का एक बड़ा हिस्सा अंतरिक्ष में फेंक देता है, जिससे एक अत्यंत उज्ज्वल और ऊर्जावान घटना होती है।

As a result, the stars are visible even during the day. Later their central portion contracts to about 10 km. In this stage, the stars are completely made up of neutrons and are called neutron stars. The pressure of these neutrons is independent of temperature and sufficient enough to balance the gravitational force for ever.
In simple words: Stars with initial mass between 8 and 25 times the Sun's mass become super giants, then explode as supernovae, leaving behind a dense core called a neutron star.

🎯 Exam Tip: For intermediate mass stars, the key events are the supergiant stage, supernova explosion, and the formation of a neutron star, emphasizing the role of neutron degeneracy pressure.

 

Question 3. End stages of stars having mass larger than 25 times the mass of the Sun.
Answer: After the supernova explosion, no pressure can balance the gravitational force. Hence these stars contract continuously and their gravitational force and density increase exponentially. All nearby objects get attracted towards these stars and not even light can come out of them. Light falling on these stars is completely absorbed by the star. We cannot see these stars. A very minute black hole is formed at the place of such a star. This is the end stage of these stars.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र तारों के जीवन चक्र और विकास के विभिन्न चरणों को दर्शाता है, जिसमें इंटरस्टेलर क्लाउड से लेकर कम द्रव्यमान वाले तारे (Low mass star) के सफेद बौने (White dwarf) में बदलने और उच्च द्रव्यमान वाले तारे (High mass star) के सुपरनोवा विस्फोट (Supernova explosion) के बाद न्यूट्रॉन तारे (Neutron star) या ब्लैक होल (Black hole) में बदलने की प्रक्रिया शामिल है। यह तारों के जन्म, विकास और मृत्यु के चरणों का एक स्पष्ट और विस्तृत प्रवाह चार्ट है।
In simple words: Stars with initial mass greater than 25 times the Sun's mass collapse completely after a supernova, forming a black hole with such immense gravity that nothing, not even light, can escape.

🎯 Exam Tip: High mass stars (over 25 solar masses) are unique because their post-supernova collapse leads to a black hole, a region where gravity is so strong that even light cannot escape, which is a key distinguishing factor.