What is dark matter?

• 96% of the universe is missing• In fact, all of the stuff we can

detect in the universe:– All of the matter– All of the energy – Only seems to account for

4% of the total size of the universe

• Scientists have been measuring the movements of millions of stars and galaxies

• And the way light bends on its way to us from distant galaxies billions of light years away

• The results say the same thing again and again

• There is a lot more out there than we see

• The straight answer: we don’t know

• Whatever it is, it doesn’t emit or absorb light like normal matter

• So we’re call it dark matter• We think it accounts for 23% of

all the matter in the universe

Pie of matter and energy[NASA]

• It’s invisible, but its gravity gives it away by bending passing light, like a lens

• The cluster of galaxies in the front of this image, called Abell 1698, is bending the light from galaxies behind, making the curved streaks

• Abell 1698 must contain dark matter to bend the light this much

Galaxy Cluster[NASA]

• This map shows dark matter has been around since as far back as we see, around 13.4 billion years billion years

• It’s scattered all through the universe, like an invisible skeleton holding normal matter in the shapes we see

Dark matter map[NASA]

• Invisible astronomical objects called Massive Compact Halo Objects - MACHOS - may explain some of it

• MACHOS are things like neutron stars and black holes, which have huge masses but give out no light

• But most dark matter is probably made from something completely mysterious

[CERN]

• Dark matter might also be made of a completely undiscovered kind of subatomic particle

• These particles are called supersymmetric particles, or sparticles for short

• Some are weakly interacting massive particles: WIMPS

• Top of the list of suspected dark matter WIMPS are neutralinos

• Making sparticles, like neutralinos, needs more powerful particle accelerators than ever before

• The LHC will be able to collide particles with enough energy to make them

• We won’t see them directly, but the huge detectors at the LHC may pick up hints of their existence

[CERN]

• The biggest machine on Earth• To glimpse a shadow world of

particles• That most of the matter in the

universe is made from…

[CERN]