Dark Matter

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Dark Matter
Da yang Jacob Daeffler
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What do we mean by dark matter?

• Material whose presence can be inferred from its
  effects on the motions of stars and galaxies, but
  which cannot be seen directly because it emits
  little or no radiation.
• Also know as missing mass.

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Contents of the Universe

• Normal Matter 4.4
• Normal Matter inside stars 0.6
• Normal Matter outside stars 3.8
• Dark Matter 25
• Dark Energy 71

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Evidence for Dark Matter

• In Galaxies
• In Clusters of Galaxies.

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Evidence for Dark Matter in Galaxies
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With out Dark Matter

• The motion of stars in a galaxy should be like
  fixed points on turning disk.

• The motion of planets in our solar system.

OR
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Scientist who first proved dark matter

• The first to provide evidence of and infer to the
  existence of a phenomenon that has come to be
  called "dark matter" was Swiss astrophysicist
  Fritz Zwicky, of the California Institute of
  Technology (Caltech) in 1933.

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Scientist who first proved dark matter

• He applied the virial theorem to the Coma cluster
  of galaxies and obtained evidence of unseen mass.
  When he compared this mass estimate to one based
  on the number of galaxies and total brightness he
  found there was 400 times more mass than
  expected.

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Rotation Curves

• Forty years after Zwicky a scientist named Vera
  Rubin found that most stars in galaxies orbit at
  roughly the same speed which means that their
  masses were more than the locations of the most
  stars. This says that more than fifty percent of
  the mass of galaxies is contained in a dark
  galactic halo.

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The visible portion of a galaxy lies deep in the
heart of a large halo of dark matter
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Evidence for Dark Matter in In Clusters of
Galaxies
We can measure the velocity of the galaxies in a
cluster and from that velocity compute the mass
and the mass is much larger than the mass of the
stars
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Does dark matter really exist?

• Our Options
• Dark matter really exists, and we are observing
  the effects of its gravitational attraction
• Something is wrong with our understanding of
  gravity, causing us to mistakenly infer the
  existence of dark matter

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YES!

• Dark matter really exists, and we are observing
  the effects of its gravitational attraction
• Something is wrong with our understanding of
  gravity, causing us to mistakenly infer the
  existence of dark matter
• Because gravity is so well tested, most
  scientists prefer option 1

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Composition of Dark Matter

• Dark matter can be categorized by either baryonic
  or non-baryonic
• Baryonic contains baryons which are protons and
  neutrons. Examples are non-luminous gas, MACHOs
  (massive compact halo object) and brown dwarfs

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NonBaryonic

• Consists of nonbaryonic particles such as
  electrons and neutrinos
• Hot dark matter-nonbaryonic particles that move
  ultrarelativistically.
• Warm dark matter-nonbaryonic particles that movie
  relativistically.
• Cold dark matter-nonbaryonic particles that move
  non-relativistically.

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Types of Dark Matter

• Ordinary Dark Matter (MACHOS)
• Massive Compact Halo Objects
• dead or failed stars in halos of galaxies
• Extraordinary Dark Matter (WIMPS)
• Weakly Interacting Massive Particles
• mysterious neutrino-like particles

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Role of Dark Matter in galaxy formation
Gravity of dark matter is what caused
protogalactic clouds to contract early in
time Dark matter is still pulling things
together After correcting for Hubbles Law, we
can see that galaxies are flowing toward the
densest regions of space
?
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Summary

• What is Dark Matter
• Evidence of Dark Matter
• Composition of Dark Matter
• Types of Dark Matter
• Role of Dark Matter in galaxy formation