A100H–Exploring the Universe: Quasars, Dark Matter, Dark Energy
Martin D. Weinberg
UMass Astronomy
[email protected]
April 19, 2016
Read: Chaps 20, 21
04/19/16 – slide 1
Announcements
⊲ Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
Read: Chaps 20, 21
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
04/19/16 – slide 2
Announcements
⊲ Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
Read: Chaps 20, 21
Final Exam: Friday 29 Apr at 10:30 am–12:30 pm, here!
Orchard Hill observing
⊲
⊲
Open on Thursdays when weather is good
See http://www.astro.umass.edu/~orchardhill
for details
04/19/16 – slide 2
Announcements
⊲ Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
Final Exam: Friday 29 Apr at 10:30 am–12:30 pm, here!
Orchard Hill observing
Today: Quasars and Active galaxies
⊲
⊲
⊲
⊲
Dark Matter & Dark Energy
⊲
⊲
⊲
Read: Chaps 20, 21
What are quasars?
What is the power source for quasars and other
active galactic nuclei?
Do supermassive black holes really exist?
How do quasars let us study gas between the
galaxies?
What is dark matter & dark energy?
What is the evidence for dark matter?
Does dark matter really exist?
04/19/16 – slide 2
Quasars
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
The highly redshifted spectra of quasars indicate large
distances
From brightness and distance we find that luminosities
of some quasars are > 1012 LSun
Variability shows that all this energy comes from region
smaller than solar system
Read: Chaps 20, 21
04/19/16 – slide 3
Quasars
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
Quasar is an abbreviation for “quasi-stellar object”
⊲
Quasar in a
galaxy
Their spectra looks like those of stars
But way too bright to be seen at observed redshift
It took decades to figure out what is going on
Their existence is consistent with supermassive black
holes at the centers of galaxies
Read: Chaps 20, 21
04/19/16 – slide 4
Quasars
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
Quasar is an abbreviation for “quasi-stellar object”
⊲
The accretion
disk
around
the black hole
Their spectra looks like those of stars
But way too bright to be seen at observed redshift
It took decades to figure out what is going on
Their existence is consistent with supermassive black
holes at the centers of galaxies
Read: Chaps 20, 21
04/19/16 – slide 4
Thought question
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
What can you conclude from the fact that quasars usually
have very large redshifts?
Read: Chaps 20, 21
(A) They are generally very distant
(B) They were more common early in time
(C) Galaxy collisions might turn them on
(D) Nearby galaxies might hold dead quasars
04/19/16 – slide 5
Thought question
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
What can you conclude from the fact that quasars usually
have very large redshifts?
(A) They are generally very distant
(B) They were more common early in time
(C) Galaxy collisions might turn them on
(D) Nearby galaxies might hold dead quasars
All of the above!
Read: Chaps 20, 21
04/19/16 – slide 5
Quasars and collisions
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
Galaxies around
quasars sometimes
appear disturbed
by collisions
04/19/16 – slide 6
Non-thermal emission
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
Synchrotron emission:
⊲
Read: Chaps 20, 21
Electron spirals around magnetic field line
Accelerating electron emits photons
Relativistic speeds
04/19/16 – slide 7
Non-thermal emission
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
Synchrotron emission:
⊲
Read: Chaps 20, 21
Electron spirals around magnetic field line
Accelerating electron emits photons
Relativistic speeds
04/19/16 – slide 7
Distribution of wavelengths
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Quasars powerfully radiate energy over a very wide range of
wavelengths, indicating that they contain matter with a wide
range of temperatures
Read: Chaps 20, 21
04/19/16 – slide 8
Radio Galaxies
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Radio galaxies contain active nuclei shooting out vast jets of
plasma that emits radio waves coming from electrons moving
at near light speed
Read: Chaps 20, 21
04/19/16 – slide 9
Radio Galaxies
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Radio galaxies contain active nuclei shooting out vast jets of
plasma that emits radio waves coming from electrons moving
at near light speed
Read: Chaps 20, 21
04/19/16 – slide 9
Radio Galaxies
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
The lobes of radio galaxies can extend over hundreds of
millions of light years
Read: Chaps 20, 21
04/19/16 – slide 10
Jets
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
An active galactic nucleus can
shoot out blobs
of plasma moving at nearly the
speed of light
Speed of ejection
suggests
that a black hole
is present
04/19/16 – slide 11
Origin of Jets
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Jets are thought to come from twisting of magnetic field in the
inner part of accretion disk
Read: Chaps 20, 21
04/19/16 – slide 12
What produces the jets?
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
Rotating disk winds up magnetic
field
Gas heated, ionized at inner
edge of disk
Electrons accelerated by magnetic field
Emits synchrotron radiation
04/19/16 – slide 13
Observations of disks and jets
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
Disk: 75 ly (250 pc) in diameter
04/19/16 – slide 14
Jets
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
Radio galaxies
don’t
appear
as
quasars because dusty
gas
clouds
block
our
view
of
accretion
disk
04/19/16 – slide 15
Appearance depends on disk orientation
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
Accretion disk EDGE on:
⊲
⊲
Read: Chaps 20, 21
⊲
See both jets, double-lobed radio source
Hot accretion disk hidden by cooler disk at larger
radii
04/19/16 – slide 16
Appearance depends on disk orientation
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
Accretion disk EDGE on:
⊲
⊲
Read: Chaps 20, 21
⊲
See both jets, double-lobed radio source
Hot accretion disk hidden by cooler disk at larger
radii
Accretion disk TILTED:
⊲
⊲
⊲
See both blackbody radiation from disk and
synchrotron radiation from jets
Very luminous ⇒ Quasar
Less luminous ⇒ Radio galaxy
04/19/16 – slide 16
Appearance depends on disk orientation
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
Accretion disk EDGE on:
⊲
⊲
⊲
Accretion disk TILTED:
⊲
⊲
⊲
See both blackbody radiation from disk and
synchrotron radiation from jets
Very luminous ⇒ Quasar
Less luminous ⇒ Radio galaxy
Accretion disk FACE on:
⊲
⊲
Read: Chaps 20, 21
See both jets, double-lobed radio source
Hot accretion disk hidden by cooler disk at larger
radii
Intense source of Synchrotron emission
Called a Blazar
04/19/16 – slide 16
Characteristics of Active Galaxies
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
Luminosity can be enormous (> 1012 LSun )
Luminosity can rapidly vary (comes from a space smaller
than solar system)
Emit energy over a wide range of wavelengths (contain
matter with wide temperature range)
Some drive jets of plasma at near light speed
04/19/16 – slide 17
What is the power source for quasars and other active
galactic nuclei?
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
04/19/16 – slide 18
What is the power source for quasars and other active
galactic nuclei?
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Accretion of gas onto a supermassive black hole appears to be
the only way to explain all the properties of quasars
Read: Chaps 20, 21
04/19/16 – slide 18
Energy from a Black Hole
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
Gravitational potential energy of matter falling into black
hole turns into kinetic energy
Friction in accretion disk turns kinetic energy into
thermal energy (heat)
Heat produces thermal radiation (photons)
This process can convert 10-40% of E = mc2 into
radiation
04/19/16 – slide 19
What about the luminosity?
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
Blackbody radiation comes from
an accretion disk of hot gas
Friction causes gas to slowly fall
into hole
Friction heats the disk, light
comes from the inner edge of accretion disk
Instabilities in the accretion disk
cause the variations in luminosity
04/19/16 – slide 20
Do supermassive black holes really exist?
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
04/19/16 – slide 21
Do supermassive black holes really exist?
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Orbital speed and distance of gas orbiting center of M87
indicate a black hole with mass of 3 billion MSun
Read: Chaps 20, 21
04/19/16 – slide 21
Do supermassive black holes really exist?
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
Orbits of stars at
center of Milky
Way stars indicate
a black hole with
mass of 4 million
MSun
04/19/16 – slide 22
Black holes in galaxies
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
Many nearby galaxies—perhaps all of them—have
supermassive black holes at their centers
These black holes seem to be dormant active galactic
nuclei
All galaxies may have passed through a quasar-like stage
earlier in time
04/19/16 – slide 23
Black holes in galaxies
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
Mass of a galaxy’s
central black hole
is closely related
to mass of its bulge
04/19/16 – slide 24
Black holes in galaxies
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
Development
of
central black hole
must be related to
galaxy evolution,
somehow
04/19/16 – slide 24
Interacting galaxies: feeding the monster
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Observed to be at the center of distant galaxies
The fuzzy extension and irregular morphology typical of
interacting galaxies
Galaxy interactions deposit into the nuclear regions to
feed the Black Hole
Stellar bars might be able to funnel gas into the nucleus
from the disk of the galaxy
[Stars][Gas]
Read: Chaps 20, 21
04/19/16 – slide 25
How do quasars let us study gas between the galaxies?
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
04/19/16 – slide 26
How do quasars let us study gas between the galaxies?
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
Gas clouds between a quasar and Earth absorb some of a
quasar’s light
04/19/16 – slide 26
How do quasars let us study gas between the galaxies?
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
Gas clouds between a quasar and Earth absorb some of a
quasar’s light
We can learn about protogalactic clouds by studying the
absorption lines they produce in quasar spectra
04/19/16 – slide 26
Summary
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
What are quasars?
⊲
Active galactic nuclei are very bright objects seen in
the centers of some galaxies, and quasars are the
most luminous type
What is the power source for quasars and other active
galactic nuclei?
⊲
The only model that adequately explains the
observations holds that supermassive black holes are
the power source
04/19/16 – slide 27
Summary
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
Do supermassive black holes really exist?
⊲
Observations of stars and gas clouds orbiting at the
centers of galaxies indicate that many galaxies, and
perhaps all of them, have supermassive black holes
How do quasars let us study gas between the galaxies?
⊲
Absorption lines in the spectra of quasars tell us
about intergalactic clouds between those quasars
and Earth
04/19/16 – slide 28
Unseen influences
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
Dark Matter: An undetected form of mass that emits
little or no light but whose existence we infer from its
gravitational influence
Dark Energy: An unknown form of energy that seems to
be the source of a repulsive force causing the expansion
of the Universe to accelerate
⊲
Read: Chaps 20, 21
04/19/16 – slide 29
Unseen influences
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
Dark Matter: An undetected form of mass that emits
little or no light but whose existence we infer from its
gravitational influence
Dark Energy: An unknown form of energy that seems to
be the source of a repulsive force causing the expansion
of the Universe to accelerate
⊲
Read: Chaps 20, 21
Contents of the Universe
Component
Normal Matter:
Normal Matter inside stars:
Normal Matter outside stars:
Dark Matter:
Dark Energy:
Fraction
4.4%
0.6%
3.8%
23%
73%
04/19/16 – slide 29
Evidence for dark matter in galaxies
Rotation Curve
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
We measure the mass of the solar system using the orbits
of planets
⊲
⊲
⊲
⊲
⊲
Orbital period, P
Average distance, a
a3 = P 2 ⇒ P = a3/2
2πa
a
1
Orbital velocity: v =
∝
∝√
P
P
a
4.5
Alternatively:
4
average velocity
3.5
3
GM
R
r
GM
v=
R
v2 =
2.5
2
1.5
1
0.5
0.5
1
1.5
2
2.5
3
semi-major axis
Read: Chaps 20, 21
04/19/16 – slide 30
Evidence for dark matter in galaxies
Rotation Curve
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
We measure the mass of the solar system using the orbits
of planets
Solar systems rotation curve declines because Sun has
almost all the mass
⊲
Read: Chaps 20, 21
04/19/16 – slide 30
Evidence for dark matter in galaxies
Rotation Curve
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
We measure the mass of the solar system using the orbits
of planets
Solar systems rotation curve declines because Sun has
almost all the mass
Rotation curve of galaxies stay flat with distance
1. Mass must be more spread out than in solar system
04/19/16 – slide 30
Evidence for dark matter in galaxies
Rotation Curve
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
We measure the mass of the solar system using the orbits
of planets
Solar systems rotation curve declines because Sun has
almost all the mass
Rotation curve of galaxies stay flat with distance
1. Mass must be more spread out than in solar system
2. Mass in galaxies is spread out over a larger region
than the stars
04/19/16 – slide 30
Evidence for dark matter in galaxies
Rotation Curve
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
We measure the mass of the solar system using the orbits
of planets
Solar systems rotation curve declines because Sun has
almost all the mass
Rotation curve of galaxies stay flat with distance
1. Mass must be more spread out than in solar system
2. Mass in galaxies is spread out over a larger region
than the stars
3. Most of a galaxy’s mass seems to be dark matter!
04/19/16 – slide 30
Evidence for dark matter in galaxies
Rotation Curve
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
We measure the mass of the solar system using the orbits
of planets
Solar systems rotation curve declines because Sun has
almost all the mass
Rotation curve of galaxies stay flat with distance
⊲
4.5
4
average velocity
3.5
3
2.5
2
1.5
1
0.5
0.5
Read: Chaps 20, 21
1
1.5
2
semi-major axis
2.5
3
04/19/16 – slide 30
Location of the dark matter
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
The visible portion
of a galaxy lies
deep in the heart
of a large halo of
dark matter
04/19/16 – slide 31
Dark matter in clusters
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
We can measure
the
velocities
of galaxies in a
cluster from their
Doppler shifts
04/19/16 – slide 32
Dark matter in clusters
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
The mass we find
from galaxy motions in a cluster is about 50
times larger than
the mass in stars!
04/19/16 – slide 32
Dark matter in clusters
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
Clusters contain
large amounts of
X-ray emitting hot
gas
Temperature
of
hot gas (particle
motions) tells us
cluster mass:
85%
13%
2%
dark matter
hot gas
stars
04/19/16 – slide 33
Dark matter in clusters
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Gravitational lensing, the bending of light rays by gravity,
can also tell us a cluster’s mass
Read: Chaps 20, 21
04/19/16 – slide 34
Dark matter in clusters
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
All three methods of measuring cluster mass indicate similar
amounts of dark matter
Read: Chaps 20, 21
04/19/16 – slide 35
Does dark matter really exist?
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
The Options
1. Dark matter really exists, and we are observing the
effects of its gravitational attraction
2. Something is wrong with our understanding of gravity,
causing us to mistakenly infer the existence of dark
matter
⊲
Read: Chaps 20, 21
04/19/16 – slide 36
Does dark matter really exist?
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
The Options
1. Dark matter really exists, and we are observing the
effects of its gravitational attraction
2. Something is wrong with our understanding of gravity,
causing us to mistakenly infer the existence of dark
matter
⊲
Because gravity is so well tested, most astronomers prefer
Option #1
Some observations of the Universe are very difficult to
explain without dark matter
Read: Chaps 20, 21
04/19/16 – slide 36
What is dark matter?
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
Two Basic Options
⊲
Read: Chaps 20, 21
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
04/19/16 – slide 37
What is dark matter?
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
Two Basic Options
⊲
Read: Chaps 20, 21
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!
04/19/16 – slide 37
What is dark matter?
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
Other Options
3. Axions
Introduced to solve a deep problem with QCD, the
theory of strong interactions
Low-mass, slow-moving particles
Interact weakly with other matter: hard to detect
Decay into a pair of light particles (photons)
⊲
Read: Chaps 20, 21
04/19/16 – slide 38
What is dark matter?
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
Other Options
⊲
Read: Chaps 20, 21
3. Axions
4. The Kaluza-Klein particle
Theory postulates an invisible ‘fifth dimension’
curled up in space-time
A precursor to string theory, predicts the existence of
a particle that could be a dark matter particle, which
would have the same mass as 550 to 650 protons
04/19/16 – slide 38
What is dark matter?
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
Other Options
⊲
Read: Chaps 20, 21
3. Axions
4. The Kaluza-Klein particle
5. Gravitino
Particle resulting from combining general relativity
and ‘supersymmetry’
Supersymmetry: states that all ‘boson’ particles have
a ‘superpartner’, called a photino
The gravitino would be the superpartner of the
hypothetical ‘graviton’, thought to mediate the force
of gravitation.
04/19/16 – slide 38
What is dark matter?
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
Other Options
3. Axions
4. The Kaluza-Klein particle
5. Gravitino
Particle resulting from combining general relativity
and ‘supersymmetry’
Supersymmetry: states that all ‘boson’ particles have
a ‘superpartner’, called a photino
The gravitino would be the superpartner of the
hypothetical ‘graviton’, thought to mediate the force
of gravitation.
⊲
Most people still think WIMPS are the best bet!
Read: Chaps 20, 21
04/19/16 – slide 38
Why believe in WIMPS?
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
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
⊲
Read: Chaps 20, 21
04/19/16 – slide 39
Why believe in WIMPS?
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
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: Chaps 20, 21
04/19/16 – slide 39
Why believe in WIMPS?
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
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
⊲
Read: Chaps 20, 21
04/19/16 – slide 39
Summary I
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
What is the evidence for dark matter in galaxies?
⊲
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
04/19/16 – slide 40
Summary I
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
Does dark matter really exist?
⊲
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
04/19/16 – slide 41
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
Trade off between energy of expansion and self-gravity of all the
mass and energy!
Read: Chaps 20, 21
04/19/16 – slide 42
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
Read: Chaps 20, 21
04/19/16 – slide 42
The Fate of the Universe
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
Fate of Universe
depends on the
amount of dark
matter
⊲
Read: Chaps 20, 21
04/19/16 – slide 43
The Fate of the Universe
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
Amount of dark matter is ≈ 25% of
the critical density suggesting fate is
eternal expansion
⊲
Read: Chaps 20, 21
04/19/16 – slide 44
The Fate of the Universe
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Read: Chaps 20, 21
But expansion appears to be
speeding up!
Dark energy??
04/19/16 – slide 45
The Fate of the Universe
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Estimated age depends on both dark matter and dark energy
Read: Chaps 20, 21
04/19/16 – slide 46
Accelerating Universe
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Accelerating Universe is best fit to supernova data
Read: Chaps 20, 21
04/19/16 – slide 47
Accelerating Universe
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
⊲
Accelerating Universe is best fit to supernova data
Read: Chaps 20, 21
04/19/16 – slide 47
Summary II
Announcements
Quasars
Collisions
Spectrum
Jets
Characteristics
Power source
BH in galaxies
Gas between
galaxies
Summary
Unseen influences
DM in Clusters
Does it exist?
What is DM?
Why WIMPS?
Summary I
The Fate of the
Universe
Accelerating
Universe
Summary II
Will the Universe continue expanding forever?
⊲
Current measurements indicate that there is not
enough dark matter to prevent the Universe from
expanding forever
Is the expansion of the Universe accelerating?
⊲
An accelerating Universe is the best explanation for
the distances we measure when using white dwarf
supernovae as standard candles
⊲
Read: Chaps 20, 21
04/19/16 – slide 48