11.1 Stars

Stars Stars are spherical objects in space made

of hot gases Stars radiate electromagnetic radiation

from a hot core Astronomers estimate there are more than

9000 billion billion stars in the universe

Interstellar matter: Stuff (dust and gas) between the stars

Dust obscures light from distant stars, but radio and infrared telescopes allow astronomers to observe the life cycle of stars

Nebula: Cloud of dust and gas

Star Life Cycle Gravity pulls gas and dust together inside a nebula

As the mass falls together it gets hotA protostar is formed

A star is formed when it is hot enough for a nuclear fusion reaction to start

This releases energy which keeps the core of the star hot

During this stable phase in the life of a star, the force of gravity holding the star together is balanced by the high pressure due to the high temperature

All stars go through similar cycles of birth, life and death

The path a star takes depends on the size of the star

Low Mass StarsSmall, dim, cool starsExist for most of life as red dwarf starsHydrogen fuel is burned slowly so red dwarf stars may last for 100 billion years

Near end of life they become very hot, small, dim white dwarf stars before burning out

White dwarf star size relative to Earth

Red dwarf star

Intermediate Mass Stars

Similar to our SunFaster fuel burning, may last for only 10 billion years

Near end of life they expand into a red giant before losing most of its mass and collapsing into a white dwarf and finally cooling to form a black dwarf

High Mass StarsMore than 12 times larger than our sunBurn hydrogen fuel very quickly and last only 7 billion years

Once fuel is used up massivestars become supergiants before exploding as a supernova

12-25 solar mass star supernovas collapse into a very dense hot neutron star

25+ solar mass star supernovas collapse into a black hole

Video: A Star is Born http://youtu.be/MGalnuFS2O0

Black HolesRegion of space where matter has collapsed in on itself resulting in a huge amount of mass being concentrated in an incredibly small area.

The gravitational pull of this region is so great that nothing can escape – not even light.

Black holes cannot be seen, we know they exist from the way they affect nearby dust, stars and galaxies

Most galaxies have supermassive black holes at their core

Life Cycle of Stars Flipbook You will create a flip book of images to illustrate the life cycle

of one type of star: Low, intermediate or high mass Your booklet must have a title page and minimum 12

drawings

After you complete your booklet work in groups of three (one with each type of star) to complete the worksheet

Characteristics of StarsSize – Compared relative to the mass of the sun (magnitude)

Colour – Reveals information about temperature, composition and movement

Remember that elements give off unique spectral patterns

Temperature – Red stars are coolest (~3000°C) and Blue stars are the hottest (20000°C - 35000°C)

Our yellow sun is about 6000°C

Luminosity – How brightly a star is shining

Hertzsprung-Russell Diagram

Shows the relationships between a stars temperature, luminosity and colour

A central band of stars on the graph is called the main sequence

90% of all stars fall are in the main sequenceWhen stars run out of fuel as they age they no longer fall on the main sequence

Hertzsprung-Russell Diagram

Doppler EffectLight and other forms of electromagnetic radiation travel in waves

Stretching or compression of these waves occurs when the object moves away or towards an observer

By analyzing the spectral patterns of stars astronomers can observe their movement

Blue Shift: Wavelengths compressed – Moving towards observer

Red Shift: Wavelengths stretched – Moving away from observer