COMPONENTS OF THE UNIVERSE

Chapter 11

11.1 STARS Stars are spherical objects in space

that radiate energy from their hot cores like a thermonuclear reactor.

They outnumber all other celestial bodies.

Stars have a life span like all living things on earth.

How long a star lives for depends on its mass.

Carl Sagan, an American writer and astronaut, once said “there are more stars in the Universe than grains of sand on all the beaches on the earth.”

Space is not empty, but filled with interstellar matter which is made up of gas (mainly hydrogen) and dust.

Even though only 1% of all interstellar matter is dust , it is the dust that makes it hard for astronomers to see light from distant stars.

The Birth of a Star Stars begin to form from the

materials in a NEBULA, when gravity starts acting on chunks of gas and dust. The mass grows until it finally collapses in on itself.

An early phase of star, called a protostar, is created.

If the protostar collects enough dust and gas, its core will reach 10 000 000 ºC and the atoms start to fuse together.

The Birth of a Star

The process of hydrogen atoms joining to form helium atoms is called nuclear fusion.

Nuclear fusion creates an enormous amount of energy.

It is the energy given off by fusion that causes stars to glow.

The Evolution of STARSSimilar to all living things, stars age. They all start in a NEBULA, but the path

of development differs depending on the mass of the newborn star.

The three paths are; Low Mass Stars Intermediate Mass Stars High Mass Stars

Low Mass Stars These stars start out small and

remain that way for most of their life as dim to cool red dwarfs. Red dwarfs burn their hydrogen at a much slower rate and may last for 100 billion years.

Intermediate Mass Stars These stars are similar in mass to our Sun.

They burn their hydrogen faster than low mass stars. They last about 10 billion years.

They will eventually expand into a red giant, then they collapse into a small, dim white dwarf. As it cools, it turns into a black dwarf, a dense, dark body of mostly carbon and oxygen.

High Mass Stars These stars have 12 times the mass of our

Sun. They expand and burn their gases rapidly becoming red giants. Their life span is about 7 billion years.

They have a violent ending collapsing onto themselves with a massive explosion called a supernova. When these supernovas explode they send heavy elements into space. The carbon, oxygen, and hydrogen we use on earth comes from these supernovas exploding.

BLACK HOLES When a star more than 25 times more

massive than our Sun explodes into a supernova, it becomes a black hole and collapses into itself.

Because the material is so dense and has an extraordinary amount of gravitational pull, nothing can escape its force, not even light.

BLACK HOLES Proof that black holes exist:a) material pulled toward the center of

black holes will emit radiation b) gravity from black holes affects

passing stars and galaxiesc) models show how super-dense

objects can distort light from stars

STAR SIZES Many stars visible

from Earth are much larger that our Sun.

Analyzing STAR COLOURS Two things can be determined about

stars when looking at them through powerful telescopes.

The stars colour reveals;A) temperature and compositionB) whether the star is moving away from

earth or toward earth

Colour and Temperature

RED stars are cool 3000oC YELLOW stars are hot 6000oC BLUE stars are hottest

20,000oC-35,000oC

Colour and Composition Spectroscopes are used to analyze chemical

composition. Using a spectroscope, the light emitting from a star reveals spectral bands that show certain gases in the star.

Colour and Motion Scientists use something called the “Doppler Effect”which measures changes in wavelength because ofmotion. Changes in sound waves can also be detected.When waves are analyzed it shows whether the patternof light is being compressed or extended. If a star iscoming closer toward Earth, the wavelengths of lightbecome compressed.

Section 11.1 Quiz