Universe Cycle - Universe (4)
Post Lab 

  • Exploring how galaxies evolve.
  • Comparing other components within galaxies.
  • black hole
  • neutron star
  • supernova
  • worksheet
  • Internet

Students determine if galaxy formation theory is still valid.


The names of many celestial objects are used in our everyday language. People talk about black holes, quasars, pulsars, neutron stars, supernova and many other things. Even candy, like Milky Way, is named for a galaxy.

The unit of a galaxy is a very dynamic place, in some areas stars can be born, die, and even explode! The evolution of galaxies also can be seen within the Universe. Not all galaxies were created at the same time. All of the stars that are grouped together did not all form at the same time. However it seems that some galaxies contain older stars, like the ellipsoidal galaxies. This can mean that they either didn't have that much fuel in each of the stars or that it formed the earliest and is now aging. In 1993, some astronomers felt that evidence on ellipsoidal galaxies leaned toward two galaxies that have merged.

Galaxies are composed of stars. A star is a ball of hot gas held together by its own gravity. A star forms a diffuse cloud of interstellar gas condenses due to gravity, and begins to undergo nuclear fusion. The energy release associated with fusion causes the star to shine. The energy of fusion balances the starís gravity, preventing it from collapsing. However, when a starís internal energy dwindles, the star may fade from sight into a white dwarf star, or a neutron star, an extremely high density object composed of 99% neutrons. Neutron stars are probably remnants from supernova explosions.

All phases of the stars seem to be present in galaxies and not between the empty space between the galaxies. A pulsar is a rapidly spinning neutron star. For reasons that are not fully understood, pulsars emit regular bursts "pulses" of radiation. The collapse of a super massive star may form a black hole, an object whose gravitational pull is so strong that nothing can escape its pull, not even light. A globular cluster is a roughly spherical group of hundreds of thousands to about a million stars. Globular clusters seem to be made of very old stars. A quasar (short for quasistellar radio source) is a point source, no more than one light year in diameter that emits tremendous amounts of energy, as much as hundreds of galaxies. Current hypotheses suggest that quasars are powered by super massive black holes.


  1. The worksheet has the students look at the "evolution" of some of the shapes of the galaxies. This theory claims that the spiral galaxies with large arms were probably formed with a greater burst of energy than an ellipsoidal galaxy. Go over the sequence given by this scientist (Dr. Hubble) as he explained how the evolution of the galaxies may have occurred.

  1. Science however, may change with more data. This diagram has been modified with new information. As the students looked at the different sites, they may read that new information changes this theory. If so, they should record this information on the worksheet. This worksheet tries to get the students to realize that information on the Internet can help them update their knowledge base in science.

  2. Have the students research galaxy formation on the Internet. As they do this, they will discover that the evolution they saw in the diagram is unlikely. This will help students to realize that science changes with new data and insights, and that information on the Internet can help them update their knowledge about science.

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