ASTR 1120 ASTR 1120 General Astronomy: General Astronomy: Stars & Galaxies Stars & Galaxies !NNOUNCEMENTS !NNOUNCEMENTS • Midterm #3 this Thursday 11/17; covering lect. 15-21 (and corresponding reading in Ch. 19-22) • last part of class today will be review • HW #8 due today, 5pm • HW #9 due Tue, 12/01, by 5pm ALTERNATE FINAL on Monday, Dec.7th, 5:30pm- ALTERNATE FINAL on Monday, Dec.7th, 5:30pm- 7:00pm, 7:00pm, in in Muenzinger Muenzinger E131 E131
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ASTR 1120 General Astronomy: Stars & Galaxies · Stars & Galaxies!NNOUNCEMENTS ¥ Midterm #3 this Thursday 11/17; covering lect. 15-21 (and corresponding reading in Ch. 19-22) ¥
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covering lect. 15-21 (and corresponding reading in Ch. 19-22)
• last part of class today will be review
• HW #8 due today, 5pm
• HW #9 due Tue, 12/01, by 5pm
ALTERNATE FINAL on Monday, Dec.7th, 5:30pm-ALTERNATE FINAL on Monday, Dec.7th, 5:30pm-
7:00pm,7:00pm, in in Muenzinger Muenzinger E131E131
Numerical simulations of structure formationNumerical simulations of structure formation
REVIEW
Lessons from ImaginaryLessons from Imaginary
UniversesUniverses•• Cold (Slow) dark matterCold (Slow) dark matter
works better than works better than hot (fast)hot (fast)dark matterdark matter
•• Neutrinos are too fastNeutrinos are too fast––structure would bestructure would besmeared outsmeared out
•• What is slow and darkWhat is slow and darkenough? We donenough? We don’’t knowt knowyet!yet!–– Particle experiments underParticle experiments under
wayway……....
Dark Matter and the Fate of theDark Matter and the Fate of the
UniverseUniverse
•• Expansion begins with the Big Bang (weExpansion begins with the Big Bang (we’’ll talk aboutll talk about
this after the break)this after the break)
•• At that point, everything in the universe is flungAt that point, everything in the universe is flung
apart atapart at outrageous speeds!outrageous speeds!
•• Several different models for Several different models for PastPast and and FutureFuture
depending upon the amount of depending upon the amount of dark matterdark matter
Very important diagramVery important diagram
““Average distanceAverage distance
betweenbetween
galaxiesgalaxies””
measure ofmeasure of
““expansion factorexpansion factor
of Universeof Universe””
Hubble constantHubble constant NOWNOW
sets how fastsets how fast
universe isuniverse is
expandingexpanding NOWNOWBig Bang = when distance zeroBig Bang = when distance zero
TIMETIME
SIZ
ES
IZE
NOWNOW
The expansion rate of the universe isThe expansion rate of the universe is
not necessarily constant for all timenot necessarily constant for all time
•• GRAVITYGRAVITY should SLOW should SLOW
expansion rate expansion rate !!
decelerationdeceleration
•• Different models forDifferent models for
different amounts of darkdifferent amounts of dark
mattermatter
–– LetLet’’s ignore s ignore acceleratingaccelerating for for
nownow
Since gravity is what pulls everythingSince gravity is what pulls everything
back in,back in, there must be athere must be a magic numbermagic number
•• Just the right amount of mass (in our currentJust the right amount of mass (in our current
universe) to slow down expansion but notuniverse) to slow down expansion but not
enough toenough to cause cause recollapserecollapse
•• We call this exact amount of matter, theWe call this exact amount of matter, the
CRITICAL DENSITYCRITICAL DENSITY
~10~10-29-29 grams/cm grams/cm33 = a few atoms in a closet = a few atoms in a closet
CriticalCritical Universe Universe
•• Density ofDensity of
matter =matter =
““criticalcritical
densitydensity””
•• Will expandWill expand
foreverforever, but, but
more andmore and
more slowlymore slowly
with timewith time
FlatFlat UniverseUniverse
Recollapsing Recollapsing UniverseUniverse
•• Dark matterDark matterdensity isdensity isgreatergreater than than““critical densitycritical density””
•• Expansion willExpansion willstop in thestop in thefuture, willfuture, willcollapse backcollapse backinin
–– Big CrunchBig Crunch
–– Oscillations?Oscillations?
Closed UniverseClosed Universe
Coasting UniverseCoasting Universe
•• The universeThe universehas alwayshas alwaysexpanded at theexpanded at thesame ratesame rate(no deceleration(no decelerationdue to gravity!)due to gravity!)
•• The age of theThe age of theUniverse = 1/HUniverse = 1/Hoo
Open UniverseOpen Universe
Three models for fates of universeThree models for fates of universe
CLOSEDCLOSED
OPENOPEN
FLATFLAT
Which model predicts theWhich model predicts the youngestyoungest
ageage for the universe today? for the universe today?
A.A. RecollapsingRecollapsing
(closed)(closed)
B.B. CriticalCritical
(flat) (flat)
C.C. CoastingCoasting
(open) (open)
Clicker QuestionClicker Question
•• A.A. RecollapsingRecollapsing
•• Age of universe isAge of universe is
how far to lefthow far to left
curves hitcurves hit
horizontal axishorizontal axis
(distance between(distance between
galaxies = 0)galaxies = 0)
What determines the future averageWhat determines the future average
distance between galaxiesdistance between galaxies??
A. The rate of expansion, with a slower expansionrate meaning a greater average distance
BB.. The rate of expansion, with a faster expansionrate meaning a greater average distance
C.C. Only on the density of matter in the universe.
Clicker QuestionClicker Question
What determines the future averageWhat determines the future average
distance between galaxiesdistance between galaxies??
A. The rate of expansion, with a slower expansionrate meaning a greater average distance
BB.. The rate of expansion, with a faster expansionrate meaning a greater average distance
C.C. Only on the density of matter in the universe.
Clicker QuestionClicker Question
Which model has the slowest future rate ofWhich model has the slowest future rate of
expansion?expansion?
A.A. RecollapsingRecollapsing
BB.. CriticalCritical
C. CoastingC. Coasting
Clicker QuestionClicker Question
Which model has the slowest future rate ofWhich model has the slowest future rate of
expansion?expansion?
A.A. RecollapsingRecollapsing
BB.. CriticalCritical
C. CoastingC. Coasting
Clicker QuestionClicker Question
•• Recollapse Recollapse to big crunchto big crunch::
–– Crushing heatCrushing heat
–– Destruction of all matterDestruction of all matter
–– Rebirth?Rebirth?
•• Eternal expansionEternal expansion::
–– Cold, galaxies dimmingCold, galaxies dimming
–– Star formation slowingStar formation slowing
–– Everything winds up as a brown dwarf, blackEverything winds up as a brown dwarf, blackdwarf, neutron star or black holedwarf, neutron star or black hole
What is the fate of the Universe?What is the fate of the Universe?
Is there enough dark matterIs there enough dark matter
to to recollapse recollapse the universe?the universe?
Baryonic matter:Baryonic matter: only a few % of critical density only a few % of critical density
Dark matter:Dark matter: only about 25% of what is needed only about 25% of what is needed
•• Universe should be in between the Universe should be in between the ““coastingcoasting””and and ““criticalcritical”” models models
The Universe will expand foreverThe Universe will expand forever
Which is it?Which is it?
… and with an unexpected twist…
A New Twist for the 21A New Twist for the 21stst
CenturyCentury
•• Scientists using whiteScientists using white
dwarf supernovae todwarf supernovae to
measure distancesmeasure distances
discovered somethingdiscovered something
quite strangequite strange
UsingUsing supernovae to determinesupernovae to determine
the fate of the Universethe fate of the Universe• Redshifts of the
Supernovae areSupernovae are notnot consistent even withconsistent even with
the expectations of a coasting universe!!!the expectations of a coasting universe!!!
Universe is accelerating?!?!
How can the universe beHow can the universe be
accelerating???????accelerating???????
A force that counteracts gravity?A force that counteracts gravity?
““Dark energyDark energy”–”– outweighs every other form of outweighs every other form of
mass/energy!mass/energy!
Truly an Truly an unknown force in all of physicsunknown force in all of physics
The Cosmological ConstantThe Cosmological Constant actually exists!actually exists!
(“Einstein’s Greatest Blunder” )
FourFour models for fates of universe models for fates of universe
CLOSEDCLOSED
OPENOPEN
FLATFLAT
ACCELERATINGACCELERATING
What is meant by What is meant by ““dark energydark energy””??
A.A. The energy associated with dark matter throughThe energy associated with dark matter throughE=mcE=mc22
B.B. An unknown form of energy thatAn unknown form of energy that counteractscounteractsgravity and causes the expansion of thegravity and causes the expansion of theuniverse to accelerate.universe to accelerate.
C.C. Any unknown force thatAny unknown force that acts like gravityacts like gravity
D.D. Highly energetic particles that are believed toHighly energetic particles that are believed toconstitute dark matterconstitute dark matter
E.E. The total energy in the universe after the BigThe total energy in the universe after the BigBang but before the first starsBang but before the first stars
Clicker QuestionClicker Question
What is meant by What is meant by ““dark energydark energy””??
A.A. The energy associated with dark matter throughThe energy associated with dark matter throughE=mcE=mc22
B.B. An unknown form of energy thatAn unknown form of energy that counteractscounteractsgravity and causes the expansion of thegravity and causes the expansion of theuniverse to accelerate.universe to accelerate.
C.C. Any unknown force thatAny unknown force that acts like gravityacts like gravity
D.D. Highly energetic particles that are believed toHighly energetic particles that are believed toconstitute dark matterconstitute dark matter
E.E. The total energy in the universe after the BigThe total energy in the universe after the BigBang but before the first starsBang but before the first stars
Summary of Galactic RecyclingSummary of Galactic Recycling
• Stars make new elements by fusion
• Dying stars expel gas and new elements, producinghot bubbles (~106 K)
• Hot gas cools, allowing atomic hydrogen clouds toform (~100-10,000 K)
• Further cooling permits molecules to form, makingmolecular clouds (~30 K)
• Gravity forms new stars (and planets) in molecularclouds
Gas C
ools
From HOTHOT to COLDCOLD
We observe star-gas-star cycle operating in Milky WayWe observe star-gas-star cycle operating in Milky Way’’ss
disk using many different wavelengths of lightdisk using many different wavelengths of light
Dark matter halo for galaxiesDark matter halo for galaxies
•• Dark matter extendsDark matter extendsbeyond visible part ofbeyond visible part ofthe galaxythe galaxy -- mass is-- mass is~10x~10x stars and gas!stars and gas!
•• Probably not normalProbably not normalmass that we know ofmass that we know of(protons, neutrons,(protons, neutrons,electrons).electrons).
•• Most likely subatomicMost likely subatomicparticles, as yetparticles, as yetunidentifiedunidentified (weakly(weaklyinteracting massiveinteracting massiveparticles particles –– WIMPsWIMPs?)?)
Stars appear to be
orbiting something
massive but
invisible … aa
black holeblack hole!
Orbits of stars
indicate a mass of
about 3-4 million4 million
MMsun sun withinwithin 600600
RRSchwarzchildSchwarzchild
SummarySummary
““Distance LadderDistance Ladder”” to measure universe to measure universe
Different standard candles are usefulDifferent standard candles are useful
for different distancesfor different distances
v = Ho ! d
Velocity of
Recession
(Doppler Shift)
Hubble’s
ConstantDistance
(km/sec) (km/sec/Mpc) (Mpc)
““HubbleHubble’’s Laws Law””
velocityvelocity
distancedistance
Best currentBest current
values forvalues for
expansionexpansion
HHoo = = 7171 +/- 4+/- 4
km/s/Mpckm/s/Mpc
Balloon analogy forBalloon analogy for
expanding universeexpanding universe
•• Each dot on theEach dot on the
balloon can beballoon can be
thought of as athought of as a
galaxy.galaxy.
As the balloonAs the balloon
expands, galaxiesexpands, galaxies
move farther awaymove farther away
from each otherfrom each other
Forming a Forming a diskdisk
with spiralwith spiral
•• As more materialAs more material
collapses,collapses, angularangular
momentummomentum spins itspins it
into a diskinto a disk
•• Stars now formedStars now formed
in in dense spiraldense spiral
armsarms –– disk starsdisk stars
are younger!are younger!
Angular momentum of protogalactic cloud
important in spiral galaxy formation
Making Making ellipticalsellipticals1.1. Higher density:Higher density: muchmuch
faster star formationfaster star formationuses up all the gasuses up all the gas
–– Nothing left to make aNothing left to make adiskdisk
oror
2.2. Lower spinLower spin–– Gas used up beforeGas used up before
•• Burst of star formationBurst of star formationuses up all the gasuses up all the gas
•• Leftovers:Leftovers: train wrecktrain wreck
•• EllipticalsEllipticals more commonmore commonin dense galaxy clustersin dense galaxy clusters(centers of clusters(centers of clusterscontaincontain central dominantcentral dominantgalaxiesgalaxies))
NGC 4038/39 AntennaeNGC 4038/39 Antennae
AGNs AGNs Central EnginesCentral Engines
How doHow do AGNs AGNs emit soemit somuch light in so littlemuch light in so littlespace?space?
•• They are powered byThey are powered byaccretion disks aroundaccretion disks aroundsupermassive supermassive blackblackholesholes
•• In some In some AGNsAGNs, huge, hugejets of material are shotjets of material are shotout at the poles. Theseout at the poles. Thesejets are strong radiojets are strong radiosources.sources.
JETJET
DISKDISK
REVIEW
““Central EngineCentral Engine”” -- artist -- artist’’s conceptions conception
•• Disk itself may orDisk itself may ormay not be obscuredmay not be obscuredby dustby dust
•• If bright nucleus isIf bright nucleus isvisible, looks like avisible, looks like aquasarquasar,, if not, thenif not, thenits aits a radio galaxyradio galaxy