THE LIFE CYCLE OF A STAR What is

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 450 x smaller to over 1000 x 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 Stars Path 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/astronomyactivities/life-of-stars. html

Types of Stars PATH TWO Massive Stars

Massive Stars • Massive stars have a mass 3 x times that of the Sun. • Some are 50 x 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 6 A - 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 6 B- 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 2000 C to above 30, 000 C, 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 100 x the Sun. If have diameters up to 1000 x that of the Sun and have luminosities often 1, 000 x 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 8000 C 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.