Dark Matter
By Joel Tome
Period 3
What is Dark Matter?
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The mass in galaxies and
galactic clusters inferred to
exist:
 by rotational properties of
galaxies
 bending of light
 and other techniques
 but has not been confirmed to
exist by observations at any
electromagnetic wavelength
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Originally called missing mass
Dark Matter on a Molecular Level
►
►
decoupled from the rest of the
universe since before the time
primordial nucleosynthesis
began
experienced large fluxuations in
density distribution since early
in the history of the universe
Properties
► forms
large-scale clumping and other mass
distributions in the universe
► controls overall mass distribution in the universe
 without affecting the microwave background radiation
 or any other observational constraints in the universe
► drew
gas and other matter into the vicinity of
peaks in its distribution over universe’s history
► Covers anywhere between 20-85% of the universe
Two Theories of Creation
► Hot
Dark matter
 of very lightweight particles, even lighter than
electrons
 may be composed of neutrinos
 development of superclusters, and vast empty
regions called voids
 do not explain the smaller-scale structures
Cold Dark matter
► consists
of heavy particles that formed in
the earliest microseconds (10^-43 second
after the big bang)
► strong, weak, and electromagnetic forces
still unified
 can explain the formation of both large-scale
and small-scale structures in the universe
Fritz Zwicky (1898-1974)
► Swiss
astrophysicist
► examined a cluster of
galaxies in
constellation Coma
Berenices (Berenice's
Hair) in 1933
► Noticed high velocity
of individual galaxies
 Could have escaped
from g attraction
Zwicky’s Conclusion
► Amount
of matter actually present must be
greater than was visible
 Used doppler shifts to confirm invisible material
Milky Way
► Research
 Milky Way contain
invisible matter
► Exerting
gravitational
influence
► Most from galactic halo
(10 times D of visible
galaxy)
 Galactic Halo cannot be
seen (dark matter)
Two theories on current Dark Matter
Ordinary matter not yet detected
(from large objects that give off
little light)
► Brown Dwarf
 Material composition of a star
but…
► Contains too little mass to
permit core to initiate
thermonuclear fusion
► White Dwarf
 Low mass may actually make
up half of dark matter in
universe
► Black Holes
 Another massive compact halo
object (MACHO)
►
Not Accepted because…
► There
are too few
MACHOs to account for
all dark matter in the
universe
Theory 2
► Weak
interaction but
massive particles
(WIMP)
► Could explain cold dark
matter
► Hypothetical form of
matter: nonbaryonic
matter
 Doesn’t contain
protons/neurons
Impact
►
►
Thought to play a crucial
role in determining fate of
universe
Based on mass in the
universe, will it continue to
expand OR shrink under its
own gravity
Video
► http://videos.howstuffworks.com/nasa/1356
2-chandra-dark-matter-video.htm
Works Cited
Angelo, Joseph A., Jr. "dark matter." Science Online. Facts On File, Inc. Web. 15 Apr.
2011.
<http://www.fofweb.com/activelink2.asp?ItemID=WE40&SID=5&iPin=ESA0690&SingleR
ecord=True>.
► "Dark matter." Gale Encyclopedia of Science. Ed. K. Lee Lerner and Brenda Wilmoth
Lerner. 4th ed. Detroit: Gale Group, 2008. Discovering Collection. Gale. Mid-Pacific
Institute. 15 Apr. 2011
<http://find.galegroup.com/srcx/infomark.do?&contentSet=GSRC&type=retrieve&tabID
=T001&prodId=DC&docId=EJ264404
0661&source=gale&srcprod=DISC&userGroupName=mid&version=1.0>.
► Hooper, Dan. "Dark matter." World Book Advanced. World Book, 2011. Web. 15 Apr.
2011.
► Kusky, Timothy. "dark matter." Science Online. Facts On File, Inc. Web. 15 Apr. 2011.
<http://www.fofweb.com/activelink2.asp?ItemID=WE40&SID=5&iPin=EESS0052&Single
Record=True>.
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