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THE EVOLUTION OF STARS
Vicki MurilloAmherst Education Center
Earth ScienceMarch 2010
Objectives
After this lesson, you will be able to:
List the sequence of stages in the evolution of both low mass and high mass stars
Describe how the gas composition of a star changes as it evolves
Track the position of a star on a H-R diagram as it evolves
A Star is Born…
Eagle Nebula Orion Nebula
Image credit: http://hubblesite.org
Nebula
Nebula: a large cloud of gas and dust where stars form
A nebula contracts due to the force of gravity exerted by the particles of gas and dust.
As the particles condense and move closer together, temperature increases.
Fusion begins at 10 million degrees K (~ 18 million °F).
Energy radiates into space.
Fusion
Four hydrogen (H) nuclei combine to create one helium (He) nucleus, releasing huge amounts of energy
Image credit: http://nobelprize.org
Which Path to Take?
The life cycle of a star depends on its mass.
Low mass stars spend much more time in the main sequence stage and eventually end up as white dwarfs.
High mass stars evolve more quickly and violently. They end up as neutron stars or black holes.
Which Path to Take?
Image credit: http://essayweb.net/astronomy
Low Mass Stars
Image credits: http://hubblesite.org, http://chandra.harvard.edu, www.windows.ucar.edu
Main sequence star (Proxima
Centauri)
White Dwarf (Sirius B)
Increasing time
Nebula (Eskimo)
Red Giant (Arcturus)
Our Sun: A Low Mass Star
Image credit: http://www.theresilientearth.com, http://chandra.harvard.edu
High Mass Stars
Image credits: http://hubblesite.org, http://antwrp.gsfc.nasa.gov, www.windows.ucar.edu
Supergiant (Betelgeuse)
Main sequence star (Regulus compared to
Sun)
Supernova (M1)
Neutron Star Black Hole (NGC 1097)
Nebula (Cone)
High Mass Star Evolution
Image credit: http://astronomyonline.org
High Mass Star Evolution
Supernova: the explosion of the outer portion of a supergiant.
Neutron star: a supernova becomes a neutron star if its mass is between 1.4 and 3 times that of the Sun. Neutron stars are so dense that a teaspoonful would weigh more than 600 million tons in Earth’s gravity.
Black hole: If a supernova’s core is more than 3 times the Sun’s mass, it becomes a black hole. Its gravity is so strong that nothing can escape from it, not even light.
Recycled Matter
As supernovas explode, they release clouds of gas and dust. This material is recycled and is used to form new stars.
Crab Nebula: A supernova remnant Observers in China and Japan
recorded the supernova nearly 1,000 years ago, in 1054.
Image credit: http://hubblesite.org
Time to Assess Your Learning
Are you able to:
List the sequence of stages in the evolution of both low mass and high mass stars?
Describe how the gas composition of a star changes as it evolves?
Track the position of a star on a H-R diagram as it evolves?
Let’s give it a try!
Low Mass Stars
Image credits: http://hubblesite.org, http://chandra.harvard.edu, www.windows.ucar.edu
Main sequence star (Proxima
Centauri)
White Dwarf (Sirius B)
Increasing time
Nebula (Eskimo)
Red Giant (Arcturus)
High Mass Stars
Image credits: http://hubblesite.org, http://antwrp.gsfc.nasa.gov, www.windows.ucar.edu
Supergiant (Betelgeuse)
Main sequence star (Regulus compared to
Sun)
Supernova (M1)
Neutron Star Black Hole (NGC 1097)
Nebula (Cone)
How will the Sun’s composition change over time?
Image credits: http://www.suntrek.org
What will happen to these percentages in the future? Why?
Evolution and the H-R Diagram
Image credit: http://lcogt.net/en/book/h-r-diagram
Which stars are the youngest? Oldest? Which started as high mass stars?
Where is our Sun and what will happen to it?
