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Cosmology and extragalactic astronomy

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If M varies with radius, and v is constant. Mass proportional to radius ... This is a NaIAD detector from UKDMC, Boulby Mine. Look for recoil from 'Heavy WIMP' ... – PowerPoint PPT presentation

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Title: Cosmology and extragalactic astronomy


1
Cosmology and extragalactic astronomy
Mat Page
Mullard Space Science Lab, UCL
6. Dark matter
2
5. Dark Matter
  • This lecture
  • Dark Matter
  • where is it?
  • what could it be?
  • some experiments to find it.

3
Recap of galaxy rotation
  • Orbital velocities rise OK but then dont fall
    off.
  • Something wrong
  • Either gravity not a 1/r2 (!!)
  • or there is more mass than we can see.
  • This is dark matter

4
(No Transcript)
5
Where must the mass be?
  • Recall M r v2/G
  • If M varies with radius, and v is constant
  • Mass proportional to radius
  • for a disc thickness h, density
  • for a sphere, density
  • Must extend out to visible edge of galaxy

6
What could dark matter be?
  • Two classes of candidates
  • MACHOs
  • Massive Compact Halo Obects
  • WIMPs
  • Weakly Interacting Massive Particles

7
What could MACHOs be?
  • Discrete objects that are very difficult to
    detect
  • Brown dwarfs / large Jupiters
  • White dwarfs
  • Small black holes.

8
What could WIMPs be?
  • New particles we havent yet seen
  • Neutrinos
  • Lightest Supersymmetric particles (neutralinos)
  • Axions (Big bang remnants).

9
Detecting MACHOs
  • Machos are small and dense.
  • But they have mass, so cause curvature in
    spacetime.
  • Will focus light from a background star as they
    pass in front - star will change brightness.

10
MACHO events
  • MACHO project looked for these events.
  • 1m telescope in Australia looked at LMC every
    night possible for several years.
  • Saw some!

11
..but not many
  • Not many low-mass (planet size) MACHOs.
  • Some 0.5 Mo events (black holes, white dwarfs?)
  • MACHOs could account for UP TO 40 of dark matter.

12
Detecting WIMPs
  • Several current future experiments
  • This is a NaIAD detector from UKDMC, Boulby Mine
  • Look for recoil from Heavy WIMP
  • None confirmed yet.

13
How are they doing?
UKDM
Other planned experiments
14
But none found so far
  • Big, risky science.
  • Would be as important for particle physics as for
    cosmology.
  • Could net the Nobel prize if found.
  • But you have to detect one first.

15
Some key points about dark matter
  • 90 of the mass in the Universe
  • Most of the mass in the outer parts of galaxies.
  • Two possible candidates for dark matter
  • WIMPs
  • weakly interacting massive particles
  • searches underway, none found so far
  • MACHOs
  • massive compact halo objects
  • can only make up to 40 of dark matter
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