BACKGROUND:
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 star’s gravity, preventing it
from collapsing. However, when a star’s 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.
PROCEDURE:
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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.
