Post on 17-Jul-2015
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
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