How are stars born?

Grade 6 Science Study Guide

Test: Friday, April 4^th

How are stars born?

1. 
   All stars start as a nebula
   
2. 
   Gravity can pull some of the gas and dust in a nebula together
   
3. 
   The contracting cloud is then called a protostar
   
4. 
   A star is born when the gas and dust from a nebula become so hot that nuclear fusion starts
   

How do stars die (low or medium stars)

1. 
   The main sequence of a main star becomes a giant …the outer parts become bigger and drift into space forming a cloud of gas called planetary nebula
   
2. 
   The blue-white core of the star cools and becomes a white dwarf
   
3. 
   The white dwarf runs out of fuel and becomes a black dwarf and dies.
   

How do stars die (high mass stars)

1. 
   The red super giant explodes- this is called a supernova
   
2. 
   Materials of a supernova may form a neutron star
   
3. 
   The most massive stars become black holes
   

TERM DEFINITION

Black dwarf	What a medium mass star becomes at the end of its life
White dwarf	A star left at the core of a planetary nebula
Nebula	A large cloud of gas or dust in space
Protostar	The earliest stage of a star’s life
Supernova	A red super giant star explodes
Neutron star	The remains of a high mass star
Black hole	Exerts such a strong gravitational pull that no light escapes
Planetary nebula	A cloud of gas

The 4 main types of galaxies	Spiral Barred spiral Elliptical irregular
Spiral galaxy	-Made up of a flattened disk, a bulge at its center, and a halo -they have a variety of shapes and are classified according to the size of the bulge and the tightness and appearance of the arms -these galaxies rotate like a hurricane or whirlpool
Barred spiral galaxy	are spirals that have a bar running across the center of the galaxy
Elliptical galaxies	do not have disk or arms they are characterized by a smooth, ball shaped appearance
Irregular galaxies	tend to be smaller objects without definite shape they have hot newer stars mixed in with lots of gas and dust

Edwin P. Hubble

• 
  he identified the relationship between a galaxy’s distance and the speed with which it is moving
  
• 
  Hubble’s Law: the farther a galaxy is from Earth, the faster it is moving away from us
  
• 
  He developed a method of classifying the different shapes of galaxies with the Hubble Tuning Fork
  

The Hubble Telescope

• 
  Is a space based telescope
  
• 
  It launched from earth by means of a space shuttle in 1990
  
• 
  The 5 areas of the universe that the Hubble telescope helped us to understand are:
  
  • 
    the expanding universe, star birth, star death, black holes, and galaxy evolution
    

Star classification

Stars are classified by their:

• 
  spectra
  
• 
  temperature
  
• 
  mass
  
• 
  color
  
• 
  luminosity
  

• 
  The 7 main types of stars
  

O,B,A,F,G,K and M

• 
  group O: blue
  
• 
  group B: blue/white
  
• 
  group A: white
  
• 
  group F: white
  
• 
  group G: yellow/white
  
• 
  group K: yellow orange
  
• 
  group M: red orange
  

The H-R diagram (the Hertzsprung – Russell)	a diagram that plots star color vs. its luminosity, spectral type, temperature, and mass
Dwarf star	Are relatively small stars, up to 2o times larger than our sun and 20,000 time brighter… our sun is a dwarf star
Red dwarf	A small, cool, very faint, main sequence star..they are the most common type of star
Blue giant	A huge, very hot, blue star It is a post-main sequence star that burns helium
Super giant	Is the largest known type of star It’s an old star
White dwarf	A small, very dense, hot star that is made mostly of carbon

The life cycle of a low/ medium mass star

Birth.. nebula → protostar → main sequence star → red giant → planetary nebula → white dwarf → death.. black dwarf

The life cycle of a high mass star

Nebula → protostar → main sequence star → red super giant → supernova → neutron star → black hole