Download A100H–Exploring the Universe: Dark Matter, Dark Energy Martin D

A100H–Exploring the Universe: Dark Matter, Dark Energy
Martin D. Weinberg
UMass Astronomy
[email protected]
April 21, 2016
Read: Chap 23
04/21/16 – slide 1
Announcements
⊲ Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
Read: Chap 23
Final Exam: Friday 29 Apr at 10:30 am–12:30 pm, here!
⊲
⊲
⊲
Emphasizes Chapters 19–23
Some topics from entire course folded in . . .
Same format: approximately 2/3 multiple choice,
1/3 short answer
04/21/16 – slide 2
Announcements
⊲ Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
Read: Chap 23
Final Exam: Friday 29 Apr at 10:30 am–12:30 pm, here!
Today: Dark Matter & Dark Energy and the Big Bang
⊲
⊲
What is the evidence for dark matter and dark
energy?
What does this imply about the future of the
Universe?
04/21/16 – slide 2
Announcements
⊲ Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
Final Exam: Friday 29 Apr at 10:30 am–12:30 pm, here!
Today: Dark Matter & Dark Energy and the Big Bang
⊲
⊲
What is the evidence for dark matter and dark
energy?
What does this imply about the future of the
Universe?
Your questions?
Read: Chap 23
04/21/16 – slide 2
What is dark matter?
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
Two Basic Options for Dark Matter
1. Ordinary Dark Matter (MACHOS)
Massive Compact Halo Objects: dead or failed stars
in halos of galaxies
2. Extraordinary Dark Matter (WIMPS)
Weakly Interacting Massive Particles:
neutrino-like particles
Read: Chap 23
mysterious
04/21/16 – slide 3
What is dark matter?
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
Two Basic Options for Dark Matter
1. Ordinary Dark Matter (MACHOS)
Massive Compact Halo Objects: dead or failed stars
in halos of galaxies
2. Extraordinary Dark Matter (WIMPS)
Weakly Interacting Massive Particles:
neutrino-like particles
mysterious
Best bet!
Read: Chap 23
04/21/16 – slide 3
Why believe in WIMPS?
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
Read: Chap 23
1. There is not enough ordinary matter
2. WIMPs could be left over from Big Bang
3. Models involving WIMPs explain how galaxy formation
works
04/21/16 – slide 4
Why believe in WIMPS?
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
1. There is not enough ordinary matter
2. WIMPs could be left over from Big Bang
3. Models involving WIMPs explain how galaxy formation
works
Projected view of
n-body simulation
Read: Chap 23
04/21/16 – slide 4
Why believe in WIMPS?
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
1. There is not enough ordinary matter
2. WIMPs could be left over from Big Bang
3. Models involving WIMPs explain how galaxy formation
works
Projected view of
n-body simulation
Read: Chap 23
04/21/16 – slide 4
Why believe in WIMPS?
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
1. There is not enough ordinary matter
2. WIMPs could be left over from Big Bang
3. Models involving WIMPs explain how galaxy formation
works
“Pie diagrams”
Read: Chap 23
04/21/16 – slide 4
Why believe in WIMPS?
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
LSS data and simulations compared
⊲
Read: Chap 23
04/21/16 – slide 5
Why believe in WIMPS?
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
LSS data and simulations compared
⊲
Read: Chap 23
04/21/16 – slide 5
Why believe in WIMPS?
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
LSS data and simulations compared
⊲
Read: Chap 23
04/21/16 – slide 5
Summary I
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
What is the evidence for dark matter in galaxies?
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⊲
Rotation curves of galaxies are flat, indicating that
most of their matter lies outside their visible regions
What is the evidence for dark matter in clusters of
galaxies?
⊲
Masses measured from galaxy motions, temperature
of hot gas, and gravitational lensing all indicate that
the vast majority of matter in clusters is dark
What is the evidence for dark matter on very large
scales?
⊲
Read: Chap 23
The distribution of galaxies and clusters in the
Universe are consistent with simulations only when
dark matter is included
04/21/16 – slide 6
Dark-Matter Detection
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
If dark matter is made up of WIMPs, then millions, possibly billions, of WIMPs must pass through every square
centimeter of the Earth each second!
⊲
Read: Chap 23
04/21/16 – slide 7
Dark-Matter Detection
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
If dark matter is made up of WIMPs, then millions, possibly billions, of WIMPs must pass through every square
centimeter of the Earth each second!
⊲
Two types of experiments designed to look for WIMPS
1. Direct detection experiments
Look for the scattering of dark matter particles off
atomic nuclei within a detector
The Axion Dark Matter eXperiment (ADMX)
searches for axions
2. Indirect detection
Look for the products of WIMP annihilation
Read: Chap 23
04/21/16 – slide 7
Direct detection
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
Direct detection experiments operate deep underground
to reduce the interference from cosmic rays.
Typically use either cryogenic or noble liquid detector
technologies.
⊲
⊲
Read: Chap 23
Cryogenic detectors operating at temperatures
below 100mK, detect the heat produced when a
particle hits an atom in a crystal absorber such as
germanium.
Noble liquid detectors detect scintillation produced
by a particle collision in liquid xenon or argon.
04/21/16 – slide 8
Direct detection
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
Read: Chap 23
SLAC argon
detector
04/21/16 – slide 9
Direct detection
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
Two of the Italian DAMA (for DArk MAtter) collaboration experiments detected an annual modulation in the
event rate that they claim is due to dark matter.
As the Earth orbits the Sun, the velocity of the detector
relative to the dark matter halo will vary by a small
amount.
This claim is so far unconfirmed and unreconciled with
negative results of other experiments.
Read: Chap 23
04/21/16 – slide 10
Indirect detection
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
If WIMPs are their own antiparticle, two WIMPs could
annihilate to produce:
⊲
⊲
gamma rays
particle-antiparticle pairs
If the WIMP is unstable, WIMPs could decay into
particles
These processes could be detected indirectly through
⊲
⊲
an excess of gamma rays
anti-protons or positrons emanating from high
density regions
Fermi Gamma-ray Space Telescope is currently being
used to look for indirect signals
Read: Chap 23
04/21/16 – slide 11
Indirect detection
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
WIMPs passing through the Sun or Earth may scatter off
atoms and lose energy!
⊲
⊲
⊲
⊲
Read: Chap 23
WIMPs may accumulate at the center of these
bodies, increasing the chance of
collision/annihilation
Could observe distinctive signal in the form of
high-energy neutrinos
Such a signal would be strong indirect proof of
WIMP dark matter
Neutrino telescopes are searching for this signal
04/21/16 – slide 12
Summary I
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
Does dark matter really exist?
⊲
⊲
Read: Chap 23
Either dark matter exists or our understanding of
our gravity must be revised
What might dark matter be made of?
⊲
There does not seem to be enough normal
(baryonic) matter to account for all the dark matter,
so most astronomers suspect that dark matter is
made of (non-baryonic) particles that have not yet
been discovered
04/21/16 – slide 13
The Fate of the Universe
Will the Universe continue expanding forever?
Does the Universe have enough kinetic energy to escape its own
gravitational pull?
⊲
⊲
⊲
Application of General Relativity to the entire Universe
Solve for motion in 4-dimensional space-time
Trade off between energy of expansion and self-gravity of all the
mass and energy!
Read: Chap 23
04/21/16 – slide 14
The Fate of the Universe
Will the Universe continue expanding forever?
Does the Universe have enough kinetic energy to escape its own
gravitational pull?
⊲
⊲
⊲
⊲
Application of General Relativity to the entire Universe
Solve for motion in 4-dimensional space-time
Trade off between energy of expansion and self-gravity of all the
mass and energy!
Einstein’s equations
Rµν
1
8πG
− R gµν + Λ gµν = 4 Tµν ,
2
c
Cosmological constant
Read: Chap 23
04/21/16 – slide 14
The Fate of the Universe
Will the Universe continue expanding forever?
Does the Universe have enough kinetic energy to escape its own
gravitational pull?
Fate of Universe depends on the amount of dark matter
2-d sketch
of possible
solutions
Read: Chap 23
04/21/16 – slide 14
The Fate of the Universe
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
Closed Universe: there is enough matter in the Universe
that gravity will eventually overcome the expansion of
space
⊲
⊲
⊲
⊲
This geometry has positive curvature
Parallel lines converge
Matched Einstein’s original model without a
cosmological constant
What is the cosmological constant?
◦
◦
Read: Chap 23
Value of the energy density of the vacuum
Introduced to “hold back gravity” and achieve a
static universe
04/21/16 – slide 15
The Fate of the Universe
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
Closed Universe: there is enough matter in the Universe
that gravity will eventually overcome the expansion of
space
Open Universe: there isn’t enough matter to stop
expansion, so the Universe will continue to expand
forever at the same rate
⊲
⊲
Read: Chap 23
This space-time has negative curvature
(saddle-shaped)
Parallel lines diverge
04/21/16 – slide 15
The Fate of the Universe
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
Closed Universe: there is enough matter in the Universe
that gravity will eventually overcome the expansion of
space
Open Universe: there isn’t enough matter to stop
expansion, so the Universe will continue to expand
forever at the same rate
Flat Universe: the expansion of the Universe and the
density of matter perfectly balance out, so the Universe’s
expansion slows down over time but never quite stops
completely
⊲
⊲
Read: Chap 23
This space has no overall curvature
Parallel lines stay parallel
04/21/16 – slide 15
The Fate of the Universe
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
Read: Chap 23
04/21/16 – slide 16
The Fate of the Universe
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
Read: Chap 23
Fate of Universe
depends on the
amount of dark
matter
04/21/16 – slide 17
The Fate of the Universe
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
Read: Chap 23
Amount of dark matter is ≈ 25% of
the critical density suggesting fate is
eternal expansion
04/21/16 – slide 18
The Fate of the Universe
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
Estimated age depends on both dark matter and dark energy
Read: Chap 23
04/21/16 – slide 19
The Fate of the Universe
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
But expansion appears to be
speeding up!
⊲
Dark energy??
Read: Chap 23
04/21/16 – slide 20
The Fate of the Universe
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
But expansion appears to be
speeding up!
⊲
Dark energy??
[We invoke the existence of some
unknown physics . . . ]
Read: Chap 23
04/21/16 – slide 20
Accelerating Universe
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
Accelerating Universe is best fit to supernova data
Read: Chap 23
04/21/16 – slide 21
Accelerating Universe
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
Accelerating Universe is best fit to supernova data
Read: Chap 23
04/21/16 – slide 21
Accelerating Universe
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
Nobel Prize 2011
⊲
Read: Chap 23
04/21/16 – slide 22
Summary II
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
Will the Universe continue expanding forever?
⊲
Is the expansion of the Universe accelerating?
⊲
Read: Chap 23
Current measurements indicate that there is not
enough dark matter to prevent the Universe from
expanding forever
⊲
An accelerating Universe is the best explanation for
the distances we measure when using white dwarf
supernovae as standard candles
04/21/16 – slide 23
Summary II
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
Will the Universe continue expanding forever?
⊲
Is the expansion of the Universe accelerating?
⊲
⊲
⊲
Read: Chap 23
Current measurements indicate that there is not
enough dark matter to prevent the Universe from
expanding forever
An accelerating Universe is the best explanation for
the distances we measure when using white dwarf
supernovae as standard candles
This implies that one could travel forever in a
chosen direction!
04/21/16 – slide 23
Extrapolate the expansion back in time
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
The Universe is current expanding. Imagine reversing the
arrow of time so that the Universe is then contracting . . .
What happens?
⊲
Read: Chap 23
04/21/16 – slide 24
Extrapolate the expansion back in time
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
The Universe is current expanding. Imagine reversing the
arrow of time so that the Universe is then contracting . . .
What happens?
The density increases.
The temperature increases.
⊲
Read: Chap 23
04/21/16 – slide 24
Extrapolate the expansion back in time
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
Read: Chap 23
The Universe is current expanding. Imagine reversing the
arrow of time so that the Universe is then contracting . . .
What happens?
The density increases.
The temperature increases.
Universe becomes ionized, like the inside of a star
04/21/16 – slide 24
Extrapolate the expansion back in time
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
The Universe is current expanding. Imagine reversing the
arrow of time so that the Universe is then contracting . . .
What happens?
The density increases.
The temperature increases.
Universe becomes ionized, like the inside of a star
As we keep going, fusion may occur.
Read: Chap 23
04/21/16 – slide 24
Extrapolate the expansion back in time
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
The Universe is current expanding. Imagine reversing the
arrow of time so that the Universe is then contracting . . .
What happens?
The density increases.
The temperature increases.
Universe becomes ionized, like the inside of a star
As we keep going, fusion may occur.
Still later, the temperatures get so high that the baryons
break up into constituent sub-particles (quarks).
Read: Chap 23
04/21/16 – slide 24
Extrapolate the expansion back in time
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
The Universe is current expanding. Imagine reversing the
arrow of time so that the Universe is then contracting . . .
What happens?
The density increases.
The temperature increases.
Universe becomes ionized, like the inside of a star
As we keep going, fusion may occur.
Still later, the temperatures get so high that the baryons
break up into constituent sub-particles (quarks).
????
Read: Chap 23
04/21/16 – slide 24
Extrapolate the expansion back in time
Announcements
What is DM?
Why WIMPS?
Summary I
Dark-Matter
Detection
The Fate of the
Universe
Accelerating
Universe
Accelerating
Universe
Summary II
Back in time
⊲
The Universe is current expanding. Imagine reversing the
arrow of time so that the Universe is then contracting . . .
What happens?
The density increases.
The temperature increases.
Universe becomes ionized, like the inside of a star
As we keep going, fusion may occur.
Still later, the temperatures get so high that the baryons
break up into constituent sub-particles (quarks).
????
Realm of the Early Universe
Read: Chap 23
04/21/16 – slide 24