All the basic knowledge about dark matter and dark energy

1. Dark Matter, Dark Energy, and
the Fate of the Universe

2. Mass within Sun’s
orbit:
1011 MSun
Observable stars
and gas clouds:
~few 109 MSun

3. Dark Matter: An undetected form of mass that emits little or
no photons, but we know it must exist because we observe
the effects of its gravity
Dark Energy: An unknown form of energy that is causing
the universe to expand faster over time
Dark matter and dark energy

4. • “Normal” Matter: ~ 4.4%
– Normal Matter inside stars: ~ 0.6%
– Normal Matter outside stars: ~ 3.8%
• Dark Matter: ~ 25%
• Dark Energy ~ 71%
What is the Universe made of?

6. Spiral galaxies all tend to have flat rotation curves
indicating large amounts of dark matter

7. The visible
portion of a
galaxy lies
deep in the
heart of a
large halo of
dark matter

8. measure the
velocities of
galaxies in a
cluster from
their Doppler
shifts
Mass is 50 x
larger than
the mass in
stars!

9. Clusters contain
large amounts hot
gas: emits x rays
Temperature of hot
gas tells us cluster
mass:
85% dark matter
13% hot gas
2% stars

10. Gravitational lensing of background galaxies also tells us
the mass

14. • 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
The
Best
Bet
What is dark matter made of?

15. MACHOs do not
cause enough
lensing events to
explain all the
dark matter

16. • There’s not enough ordinary matter
• WIMPs could be left over from Big Bang
• Models involving WIMPs explain how galaxy
formation works
Why Believe in WIMPs?

17. Gravity of dark matter is what caused protogalactic clouds
to contract early in time


18. WIMPs don’t
contract to
center because
they don’t emit
photons, so
they can not
radiate away
their orbital
energy

19. Maps of galaxy positions reveal extremely large
structures: superclusters and voids

20. WIMP models agree better with observations

21. Critical
density of
matter
Not enough
dark matter
Fate of
universe
depends
on the
amount
of dark
matter
Lots of
dark matter

22. Amount of dark matter
is ~25% of the critical
density suggesting fate
is eternal expansion
Not enough
dark matter

23. But expansion
appears to be
speeding up!
Not enough
dark matter
Dark
Energy?

24. Brightness of distant white-dwarf supernovae tells us how
much universe has expanded since they exploded

25. Accelerating universe is best fit to supernova data