11.1 stars

1. 11.1 Stars

2. 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

3.  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

4. Star Life Cycle
Gravity pulls gas and dust together inside a
nebula
As the mass falls together it gets hot
A protostar is formed

5.  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

6. All stars go through similar cycles of birth, life
and death
The path a star takes depends on the size of
the star

7. Low Mass Stars
Small, dim, cool stars
Exist for most of life as red dwarf stars
Hydrogen 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

9. Intermediate Mass Stars
Similar to our Sun
Faster 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

11. High Mass Stars
More than 12 times larger than our sun
Burn hydrogen fuel very quickly and last only 7
billion years
Once fuel is used up massive
stars 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

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

14. Black Holes
Region 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

15. 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

16. Characteristics of Stars
Size – 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

17. 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 sequence
When stars run out of fuel as they age they no
longer fall on the main sequence

18. Hertzsprung-Russell Diagram

19. Doppler Effect
Light 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