The Life of a StarThe Life of a Star (15.1)(15.1)

BLM 15.1bBLM 15.1b

The Life of a StarThe Life of a Star (p. 468)(p. 468)

We say that stars have a “life” We say that stars have a “life” because they form from clouds of because they form from clouds of gas and dust and follow a predictable gas and dust and follow a predictable series of stages: series of stages:

they begin (“birth”) they begin (“birth”) they develop they develop they end (“die”).they end (“die”).

Each life might take billions of years or Each life might take billions of years or more.more.

Three types of StarsThree types of StarsThere are three types of stars:There are three types of stars:

Dwarf (same or less mass than the sun) - Dwarf (same or less mass than the sun) - 95%95%The sun is actually a dwarf.The sun is actually a dwarf.

Giant (10 times the mass of the sun) – Giant (10 times the mass of the sun) – 4%4%

Supergiant (30 times the mass of the sun) – Supergiant (30 times the mass of the sun) – 1%1%

Birth Birth All stars begin their lives as All stars begin their lives as

nebulasnebulas, which are huge clouds , which are huge clouds of dust and gases, mainly of dust and gases, mainly hydrogen and helium.hydrogen and helium.

As they swirl around, the dust As they swirl around, the dust bumps into each other and forms bumps into each other and forms larger and larger clumps.larger and larger clumps.

Early LifeEarly LifeWhen clumps have enough When clumps have enough

hydrogen and dust – nuclear hydrogen and dust – nuclear fusion starts. fusion starts. They have become They have become new stars.new stars.

They get hotter and hotter from the They get hotter and hotter from the nuclear fusion.nuclear fusion.

You would think that the larger a You would think that the larger a star is the longer it would live, star is the longer it would live, this is not true.this is not true.

Life of StarsLife of StarsDwarf starsDwarf stars undergo nuclear fusion for undergo nuclear fusion for

about 10 billion to 100 billion years. (about 10 billion to 100 billion years. (not not bright at allbright at all))

Giant starsGiant stars produce energy for a few produce energy for a few million years. (million years. (5000x’s as bright as the 5000x’s as bright as the SunSun) )

Supergiant starsSupergiant stars produce energy for produce energy for about a million years. (about a million years. (extremely brightextremely bright) )

Giant and Supergiant stars use their energy Giant and Supergiant stars use their energy faster. This is why they are brighter and faster. This is why they are brighter and don’t last as long.don’t last as long.

Old AgeOld AgeWhen a star nears the end of its lifeWhen a star nears the end of its life

it starts to use the last of it’s it starts to use the last of it’s hydrogen fuel and swell slightly hydrogen fuel and swell slightly larger as pressure reduces and turns larger as pressure reduces and turns red (cools down).red (cools down).

SupernovaSupernova

A A supernovasupernova is an enormous final is an enormous final explosion of a star as it uses up the explosion of a star as it uses up the last of it’s fuel. last of it’s fuel.

The center of the star collapses inward The center of the star collapses inward to become either a neutron star or a to become either a neutron star or a black hole. black hole.

The outer layers of the star explode and The outer layers of the star explode and the gas and dust are pushed outwards.the gas and dust are pushed outwards.

What is left?What is left?Dwarf starsDwarf stars - cool and fade away. - cool and fade away.

Giant starsGiant stars - the core packs together as - the core packs together as a a neutron starneutron star. An extremely dense . An extremely dense star composed of neutrons.star composed of neutrons.

Supergiant starsSupergiant stars - the core packs - the core packs together as a black hole. A small, very together as a black hole. A small, very dense object with a force of gravity so dense object with a force of gravity so strong that nothing can escape from it. strong that nothing can escape from it. Even light cannot get away from its Even light cannot get away from its surface so they can exist undetected.surface so they can exist undetected.

SummarySummarySee page 469 in See page 469 in

your text.your text.

Handout BLM Handout BLM 15.1b.15.1b.

SummarySummaryDwarfsDwarfs GiantsGiants SupergiantsSupergiants

Same size as SunSame size as Sun 10 times mass of 10 times mass of SunSun

30 times mass of 30 times mass of SunSun

95%95% 4%4% 1%1%From sm. NebulaFrom sm. Nebula From med. NebulaFrom med. Nebula From very lg. From very lg.

NebulaNebula in heat and sizein heat and size in heat and sizein heat and size in heat and sizein heat and size

Last 10-100 billion Last 10-100 billion yryr

Lasts 3-5 million yrLasts 3-5 million yr Lasts 1 million yearsLasts 1 million years

Not very brightNot very bright BrightBright very brightvery brightGases drift awayGases drift away Core collapsesCore collapses Core collapsesCore collapses

Fades awayFades away Neutron star Neutron star createdcreated

Black hole createdBlack hole created

Questions p. 471Questions p. 4711. Describe how a star forms.1. Describe how a star forms.Stars form from huge clouds of dust Stars form from huge clouds of dust

and gases called and gases called nebulasnebulas. The dust . The dust and gases swirl around, forming and gases swirl around, forming clumps. These clumps attract each clumps. These clumps attract each other because of gravity and grow other because of gravity and grow larger and larger. When they are larger and larger. When they are large and dense enough, they large and dense enough, they begin to produce large amounts of begin to produce large amounts of light energy and other forms of light energy and other forms of energy.energy.

Questions p. 471Questions p. 4712. Describe the differences between the 2. Describe the differences between the

life of a low-mass star and that of a star life of a low-mass star and that of a star 10 times the Sun’s mass.10 times the Sun’s mass.

Low-mass stars cool down and swell up Low-mass stars cool down and swell up into a red giant. Outer layers drift away into a red giant. Outer layers drift away and the star shrinks to become a white and the star shrinks to become a white dwarf which will cool and fade away. dwarf which will cool and fade away.

High-mass stars swells into a red High-mass stars swells into a red supergiant which undergoes a supergiant which undergoes a supernova. This leaves behind either a supernova. This leaves behind either a neutron star or a black hole depending neutron star or a black hole depending on the mass of the original star. on the mass of the original star.

Questions p. 471Questions p. 4713. What is a supernova?3. What is a supernova?A supernova is a type of explosion that A supernova is a type of explosion that

occurs when the source of energy of occurs when the source of energy of a high-mass star is used up. The a high-mass star is used up. The outer layers of the star expand outer layers of the star expand outward rapidly.outward rapidly.

Test Review QuestionsTest Review QuestionsCh.13Ch.13: 13.1, 13.3, 13.4: 13.1, 13.3, 13.4

p. 434-435: Questions 7, 11.p. 434-435: Questions 7, 11.

Ch. 14Ch. 14: 14.7, 14.10, 14.11: 14.7, 14.10, 14.11p. 464-465: Questions 3a, 8-10, 11-14. p. 464-465: Questions 3a, 8-10, 11-14.

Ch.15Ch.15: 15.1: 15.1p. 484-485: Questions 2-4, 6-8.p. 484-485: Questions 2-4, 6-8.

Topics by section:Topics by section:13.1:13.1: Basic Terms, How planet’s move, Key differences Basic Terms, How planet’s move, Key differences

between planets and stars.between planets and stars.13.3:13.3: Rotation vs. Revolution, How does this relate to Rotation vs. Revolution, How does this relate to

the Earth’s days, years, seasons.the Earth’s days, years, seasons.13.4:13.4: Constellations – know how to locate on a star map. Constellations – know how to locate on a star map.14.7:14.7: Composition of the Sun, Parts of the Sun, How the Composition of the Sun, Parts of the Sun, How the

Sun’s energy is made.Sun’s energy is made.*14.10:*14.10: 5 key characteristics of the Sun: Colour, Size, 5 key characteristics of the Sun: Colour, Size,

Temperature, Brightness, and Spectrum.Temperature, Brightness, and Spectrum.14.11:14.11: 4 Types of Galaxies, Which is ours? 4 Types of Galaxies, Which is ours?*15.1:*15.1: Stages of the life of a star, Know a little about Stages of the life of a star, Know a little about

each stage.each stage.