Dark Matters
Steinn Sigurðsson
Astro 120-33 - Mar 2017
Options for Dark Matter
Massive Compact Halo Objects - MACHOs
“normal” stuff, in lumps - but does not shine
Weakly Interacting Massive Particles - WIMPs
something new - a new particle not known
to physics that does not interact with light
Or…???
MACHOs?
Could be dark massive objects
dark “lumps” - pebble size to size of (very) small galaxies
Like dwarf stars - M stars
Or white dwarfs - dead stars
Or black holes - what mass
stellar?
tiny - from Big Bang?
massive?
Transparency
Look not just using visible light - also
infrared (heat) radiation, microwave and
radio, ultra-violet and x-rays
Don’t see anything - rules out some stuff:
eg “snowballs” would be seen in infrared
looking for things that are completely
transparent to all forms of light. How?
microLensing
IF halo is made from MACHOs then we can
see them through microlensing
Look for background stars - Magellanic
clouds or Milky Way bulge - getting brighter
due to faint or unseen foreground halo
object passing in front of the star
Been done - MACHO and OGLE projects
Quantity matters
There are MACHOs in the galaxy We see them in
microlensing
They are planets, dead stars, some very faint red
dwarf stars, and stray black holes
Microlensing now used to find planets!
There are not nearly enough of them to be the Cold
Dark Matter - would need 100 times more MACHOs
then we find.
MACHOs are NOT the Dark Matter we are looking for
WIMPs?!
Standard Model of particle physics explains the
particles that make up normal matter
Also predicts a number of other particles, including
massive ones
None of those can explain WIMPs
Need new particles beyond the Standard Model
Standard Model is not complete, expect more physics
beyond it - problem is there are lots of particles
predicted by different theories - too many
What’s the matter
What is the nature of the Cold Dark Matter?
Constitutes ~ 20-25% of the mass of the universe
‘bout 5-6 times more than of normal “baryonic” matter
MACHOs are mostly ruled out
Must be WIMPs, but WHAT?
Many, many candidates from particle physics - all of
them hypothetical, not a single one confirmed
Standard Model
Neutrons+protons are composite:
quarks (1/3 and 2/3 electric charge)
flavours: up, down; strange, charm; top bottom
always confined never seen free
usually sets of 2 or 3
also carry “colour“ charge: red, green or
blue
gluons - carry strong nuclear force, hold quarks together
other particles like pions and kaons made from
quark and gluon combos - most are unstable.
Standard Model 2
electron - plus heavy partners, muon μ and tau τ neutrinos: νe νμ ντ So three “generations” for each type of particles
photon - γ - transmits electro-magnetic force
W and Z particles - transmits weak nuclear force
H - Higgs boson - spin 0 particle, gives mass to
other particles g - graviton - spin 2 - transmits gravity
http://CPEPweb.org
Dark Matter
Dark matter particle MUST be beyond
Standard Model - a new particle - like…
Lightest Supersymmetric Partner
Axion
Sterile neutrinos
Higgs
WIMPzillas
Manyfold matter
Shadow matter
Really weird stuff...