THE LIFE CYCLE OF A STAR

What is a Star?•Stars are glowing gas that

start in Nebulae. •They vary in size, mass and

temperature, diameters ranging from 450x smaller to over 1000x larger than that of the Sun.

•Surface temperature can range from 3,000 degrees Celsius to over 50,000 degrees Celsius.

Star Color •The color of a star is determined by its temperature▫Hottest stars are

blue ▫Coolest stars are

red.

•The Sun is 5,500 degrees Celsius, and appears yellow

Brightness•The energy produced is by nuclear fusion

in the core. •The brightness is measured in magnitude

Measuring•There are two ways to measuring the

brightness of a star:▫Apparent magnitude is the brightness

seen from Earth▫Absolute magnitude which is the

brightness of a star seen from a standard distance of 10 parsecs (32.6 light years).

Stars can be plotted on a graph using the Hertzsprung Russell Diagram

• It shows that the temperature coincides with the luminosity

•Hotter the star- - higher the luminosity

•You can tell the size of each star from the graph ▫higher the radius the

higher the temperature and luminosity.

Homework

•Star Types - - Color, surface Temperature, and characteristics Worksheet

•HR Diagram Worksheet

How a star is formed and the types of stars…

Where they are born…•In nebulae. •Huge clouds of dust and gas collapse under

gravitational forces, forming protostars.

Types of StarsPath ONE(Small Stars)

Small Stars•Have a mass up to one and a half times

that of the Sun. ▫Stage 1- Stars are in a Nebula, that

condenses into a huge globe of gas and dust it contracts under its own gravity.

•Stage 2 – It then heats up and starts to glow forming Protostars. ▫Central temperature can reach 15

million degrees centigrade.

•Stage 3 - Nuclear reactions start and hydrogen fuses to form helium.

•Stage 4 - The star begins to release energy, stopping it from contracting and causes it to shine. It is now a Main Sequence Star. (This is our sun)

•Stage 5 - A star of one solar mass remains in main sequence for about 10 billion years, until all of the hydrogen has fused to form helium.

•Stage 6 - The helium core now starts to contract further and reactions begin to occur in a shell around the core.

•Stage 7 - The core is hot enough for the helium to fuse to form carbon. The outer layers begin to expand, cool and shine less brightly. The expanding star is now called a Red Giant.

•Stage 8 - The helium core runs out, and the outer layers drift of away from the core as a gas shell, called a Planetary Nebula.

•Stage 9 - The remaining core (80% of the original) is now in its final stages. The core becomes a White Dwarf the star eventually cools and dims.

•Stage 10- When it stops shining, the now dead star is called a Black Dwarf.

Homework

•Start Project: life Cycle of a star

•http://www.kbteachers.com/astronomy-activities/life-of-stars.html

Types of Stars

PATH TWOMassive Stars

Massive Stars

•Massive stars have a mass 3x times that of the Sun.

•Some are 50x that of the Sun

•Stage 1- Nebula as well•Stage 2 - Massive stars develop similar to

a small star until it reaches its main sequence stage.

•The stars shine steadily until the hydrogen has fused to form helium (it takes billions of years in a small star, but only millions in a massive star).

•Stage 3 - The massive star becomes a Red Supergiant and starts off with a helium core surrounded by a shell of cooling, expanding gas.

•The massive star is much bigger in its expanding stage.

•Stage 4 - In the next million years a series of nuclear reactions occur forming different elements in shells around the iron core.

•Stage 5 - The core collapses in less than a second, causing an explosion called a Supernova, in which a shock wave blows of the outer layers of the star. (The actual supernova shines brighter than the entire galaxy for a short time).

•Stage 6A - Sometimes the core survives the explosion. If the surviving core is between 1.5 - 3 solar masses it contracts to become a tiny, very dense Neutron Star.

•Stage 6B- If the core is much greater than 3 solar masses, the core contracts to become a Black Hole.

HOMEWORK

•FINISH PROJECT TIMELINE

Key Vocab!!!

NEBULA

•A nebula is a cloud of gas (hydrogen) and dust in space.

•Nebulae are the birthplaces of stars. •There are different types of nebula.

▫Emission Nebula▫Reflection Nebula▫Dark Nebula▫Planetary Nebula

STAR •A star is a luminous globe of gas producing

its own heat and light •They are born from nebulae•consist mostly of hydrogen and helium gas. •Surface temperatures range from 2000C to

above 30,000C, and the corresponding colors from red to blue-white.

•The brightest stars have masses 100 times that of the Sun and emit as much light as millions of Suns.

• They live for less than a million years before exploding as supernovae.

•The faintest stars are the red dwarfs, less than one-thousandth the brightness of the Sun.

•The smallest mass possible for a star is about 8% that of the Sun (80 times the mass of the planet Jupiter), otherwise nuclear reactions do not take place.

•Objects with less than critical mass shine only dimly and are termed brown dwarfs or a large planet.

• Towards the end of its life, a star like the Sun swells up into a red giant, before losing its outer layers as a Planetary Nebula and finally shrinking to become a white dwarf.

RED GIANT•This is a large bright star with a cool

surface. • it runs on hydrogen fuel •diameter's between 10 and 100x the Sun. •If have diameters up to 1000x that of the

Sun and have luminosities often 1,000,000x greater than the Sun.

RED DWARF •These are very cool, faint and small stars,

approximately one tenth the mass and diameter of the Sun.

•They burn very slowly and have estimated lifetimes of 100 billion years.

WHITE DWARF•This is very small, hot star•White dwarfs have a mass similar to that

of the Sun, but only 1% of the Sun's diameter; approximately the diameter of the Earth.

•The surface temperature is 8000C or more

• luminosity's are 1% of the Sun or less. •White dwarfs are the shrunken remains of

normal stars

SUPERNOVA •This is the explosive death of a star, and

often results in the star obtaining the brightness of 100 million suns for a short time.

•They leave behind neutron stars and black holes.

•Supernovae are thought to be main source of elements heavier than hydrogen and helium.

NEUTRON STARS •produced when a supernova explodes,

forcing the protons and electrons to combine to produce a neutron star.

•Neutron stars are very dense.

•If its mass is any greater, its gravity will be so strong will become a black hole.

BLACK HOLES•Black holes are believed to form from

massive stars at the end of their life times.

•The gravitational pull in a black hole is so great that nothing can escape from it, not even light.

•The density of matter in a black hole cannot be measured.

•Black holes distort the space around them, and can often suck neighboring matter into them including stars.