Galaxies And The Universe Final

Front 1

Why did it take us until the 1920s to know we were in the milky way? (Three reasons)

Back 1

-. If the distance to the Milky Way center were scaled to the size of this room, then on the same scale the solar system would be the size of DNA. The galaxy is really big!
-We’re inside of it (like being in a forest and trying to see how big the forest is)
-Dust obscures visible light from stars in the disk of the galaxy, especially distant ones

Front 2

. If the distance to the Milky Way center were scaled to the size of this room, then on the same scale the solar system would be the size of ...

Back 2

a molecule of DNA (10^ 7 m)
in otherwords, the galaxy is HUGE compared to the size of the solar system.

Front 3

Distance from the solar system to the center of the galaxy is...

Back 3

25,000 Ly

Front 4

What is dust?

Back 4

• small specks of solid matter (biggest ones up to millions and billions of molecules)
• Typical size: Diameter ~ .4microns (range .01-1micron)
• Chemical composition- silicates (like sand) or carbon compounds (graphite/stoot).
• Comes from stars when they expel planetary nebulae, etc. When particles from stars cool, they congeal

Front 5

Why does dust matter?

Back 5

obscures our ability to see things
• Absorption and scattering- collectively, referred to as extinction

Front 6

Why do the best IR and visible light images come from space?

Back 6

Earth’s atmosphere is only partly transparent to IR photons

Earth’s atmosphere causes images to be blurred.

Front 7

Describe the Milky Way Galaxy.

Back 7

Disk thickness = 5,000ly. No sharp cutoff. Half the stars would be within this range. Disk has most of the dust. The bulge is right in the middle Nucleus w/black hole. There are also stay clusters, or globular clusters, in the halo or region about the dist. We are within the thick part, about 2/3rds of the way out. Why can we see things in the halo without dust? Not too much dust in the halo.

Front 8

Star Cluster

Back 8

little piece of a galaxy at helps gravitationally; group of stars which all formed at the same time, so they have the same age. Very useful to astronomers

Front 9

Globular clusters

Back 9

-have a well defined cut off
-large, 10^5-10^6 pc
-mostly in halo, but some in disk and bulge.
-Mostly halo, some a disk or bulge, few, heavy elements
-Age 10^10 years

Front 10

open cluster

Back 10

o small, 10^2,-10^3 stars
-found only in the disk of the galaxy
-has lots of heavy elements (heavier than helium)
-younger than 10^9 years

Front 11

HR diagrams of Star Clusters with Different Ages

Back 11

• Diagram 1- A= 10^7. Main sequence is very high. As the star ages, more stars die and so the main sequence turn off is 2.5 solar masses. When is 10^8 billion, it’s a regular main sequence stars.
• Massive stars leave the main sequence first.
• By obtaining Hr diagram of a star cluster, and determining the turn off point from the main sequence, you can determine the age of a cluster and therefore know the age of a cretin piece of the galaxy.
• Star clusters in halo are older with fewer heavy elements- formed before the dist.

Front 12

Elliptical Galaxies

Back 12

o Smooth, featureless, shape, in projection, some round, some flatter, but none are flatter than a 3:1 axial ratio. But what is their true three dimensional shape? We don’t always know. But in three dimensions, most are not oblate spheroids, but thiaxal ellipsoids (like a squashed football).

• There are NO YOUNG STARS and VERY LITTLE DUST AND COLD GAS in ellipticals… in a way, they are dead. No potential for new stars.

Front 13

• Spirals

Back 13

o all contain disk and bulge
o Bulge- not thin, significantly extended in all 3 directions. More centrally concentrated. Like an E galaxy in many ways.
o Disk- Thin, less centrally concentrated.
• Type Sa- bigger bulge (less disk)
• In spirals, disks contain gas, dust & ongoing star formation, usually in spiral arms. STILL ALIVE!

Front 14

• Lenticulars (Sø’s)

Back 14

o Contain disk and bulge (like spirals)
o This has no gas, dust or ongoing star formation, unlike spirals
o IE, if all the gas and dust is used up in a spiral, it becomes this.

Front 15

• Limitations of Hubble Classification system

Back 15

• Only based on visual appearance, may not be based upon most fundamental differences. Not on quantified measurements
• Ellipticals are based upon apparent shape, but that does not represent the true shape
• Bars are not so fundamental. Not all or nothing! There’s a continuum of bar strengths, from weak bars to really strong bars
• Suggests elliptical evolves into Spirals, but not true. But spirals can turn into elliptical, not a good evolutionary sequence.
• Leaves out most of the galaxies in the universe

Front 16

Other galaxies not covered by the Hubble Classification system

Back 16

-small galaxies (most in the universe)
-interacting and disturbed galaxies → galaxies in interesting evolutionary phases.
-Low surface brightness galaxies- really really faint!
-Most massive galaxies in the universe- cD galaxies.

Front 17

Barred galaxies

Back 17

Spiral galaxies with an additional linear feature of nearly uniform brightness centered on the nucleus
• About half of spirals and Sø’s have them

Front 18

Smallest Galaxies

Back 18

• dominant type of galaxy by number but not mass. [FYI- Milk Way is bigger for a galaxy.]
• both dwarf elliptical and dwarf irregular types. 100,000xs smaller than us- “dwarf galaxy companions
o Dwarf irregulars- essentially low mass versions of spiral galaxies. Disk systems, which lack symmetry and beauty, do not have spiral arms do to the byproduct of their low mass.
o May be the building blocks for bigger galaxies, merging with each other until they are big.
ie Large Magellanic Cloud, orbits the milk way, one day might be eaten by us

Front 19

Major differences between disks and bulges/elliptical

Back 19

• Gas content- disks contain lots of cold gas. E/B’s don’t.
• Ages of Stars- disks have young stars and ongoing star formation. Ellipticals and bulges don’t.
• Shape- disk thin, bulges round.
• Motions of stars -Most stars in a disk travel in nearly circular orbits close to the disk plane. • There are roughly circular orbits in the disk plane, they orbit in the same direction and close to the same plane. Orbits are organized.
• However, in an elliptical, stars look like a swarm of bees! They orbit around the center, but in this case the stars are orbiting in different directions. Orbits are not confined to a plane.

Front 20

Spiral Arms

Back 20

• Spiral arms- spiral shaped regions of enhanced density & enhanced star formation. The amount of extra stars in an arm is modest compared to overall density, and stars move in and out of these arms
• Caused by a wave or disturbance in the disk.
• Arms are not material arms (stuff does not stay in them) but a wave feature through which stars and gas pass.

Front 21

2 reasons for excess light in the spiral arms

Back 21

o stars slow down in spiral arms, causing a “traffic jam” of all stars.
o Gas clouds are compressed and shocked on the arm. Some massive stars explode as supernovae on the backside of the arm. Star formation is thus triggered on the arms. Most luminous young stars are massive O stars, which blow up directly after formation on the arms. They explode as Type II supernovae before they move far from the arm.

Front 22

What does the space between stars contain?

Back 22

o Gas- individual atoms & molecules
o Dust- small pieces of solid matter (millions/billions of particles)
• (Mass dust is about 1% mass of gas)
o Planets, asteroids, comets, meteorites, other debris
o Photons (from lots of things)
o Magnetic fields
o Gravity & gravitational waves
o Cosmic rays- “fast gas” (nuclei, electrons moving at high speed)
o Dark matter (?)

Front 23

Things about gas

Back 23

o Primordial- created in the big bang, existed before stars and galaxies
o “recycled” through stars, stellar mass loss in all stars through solar wind (including those on the main sequence). Envelope ejection (red giant & planetary nebulae stage) Supernovae
o Stars in galaxies form from gas
o Protogalaxy (before it becomes a galaxy) is just a cloud of gas

Front 24

Hydrogen- HI

Back 24

o Simplest and most abundant element in the universe (~ ¾ of the matter in the universe by mass)
o Helium (~1/4 of the matter in the in the universe by mass)
- I means the atom has all its electrons (II means it is missing one electron)

Front 25

Spin-flip transition

Back 25

o If the spins of proton and neutron are the same, eventually is will spontaneously switch to another state. The spin of the electron will flip so that it is opposite the spin of the proton, so that proton and electron have anti-parallel shift.
o Remember: The spinning electric charges are making electric fields. Think of them like bar magnets with like ends together- they don’t like it and flip! When they flip this is easier to maintain, and it can stay like this.
o HI is an upper energy state, and when it switched is goes to a lower energy state. When the atom goes though its spontaneous spin flip transition it emits a photon.

Front 26

How do we detects hydrogen?

Back 26

o The emitted photon from a spin-flip transition is a very weak one, only 1/42 GHz, λ=21.1cm. Energy is a pathetic 5.9 * 10^-6 eV. Expressed as a temperature, this is .07K. Room temp is 300K.
o If we measure spectral line of HI, at λ = 21. cm in a given direction then we can figure out how many hydrogen atoms are in that direction. By measuring Doppler Shift, can determine gas motions, learn masses

Front 27

What makes up the mass of a galaxy?

Back 27

o Mgas/mtotal ~ 1%
o Mstars/mtotal ~ 9%

~90% is dark matter

Front 28

Where is hydrogen located in a spiral galaxy

Back 28

• HI is in disks, not bulges
o Found further from the center than the stars
• → indicates that star formation is inefficient in the outer parts of the galaxies (gas density are too low)
• allows us to measure masses of galaxies far from the center as gas clouds orbit. Ultimately will provide evidence for dark matter)

Front 29

Doppler shift

Back 29

• apparent change in λ (and in frequency eg. Electromagnetic waves) due to relative motion between source and observer
o motion along the ling of sight towards the observer (negative velocity) this causes a blueshift (λ < original λ)
o motion along the light of sign away from the observer (λ> original λ) is a redshift
• But what is something doesn’t happen along the line of sight or line of motion?
o You don’t’ have a Doppler shift.

Front 30

3 things that cause λ of light to shift:

Back 30

• Doppler shift
• Cosmological redshift
• Gravitational redshift

Front 31

Measuring Rotation Velocities of Spiral Galaxies Using Doppler Shifts of the HI 21 cm line

Back 31

• We observe three different spectrums (flux versus wavelength) for the right, left and center of the galaxy. (assume the galaxy is not moving towards or away from the earth, observed with radio telescopes). Then we compare the differences to the standard wavelength.

Front 32

Orbital speed of sun around center of the Milky Way

Back 32

220 km/sec (“fast”), .027 cm/sec
Takes sun 2 x 10^8 years to go around the Milky Way

Front 33

Rotation of the Milky Way

Back 33

• According to Newton’s and Einstein’s Law of Gravity, there is not enough mass in the known stars and gas to account for the high rotational velocities of galaxies. So...
o 1) there is some undetected and unknown form of mass which contributes to most of the mass in galaxies, called dark matter.
o 2) Maybe the law of gravity need modification? It would need modification for really large distances or small accelerations
• we don’t know which is correct. More people think that Dark Matter exists, it is more likely. However, suggestion#2 should be taken seriously.

Front 34

Why are the effects of Dark Matter felt on scales of galaxies but not within the classroom?

Back 34

• The density of dark matter relative to normal matter is low in the room but not in the galaxy.
• Dark Matter is less centrally concentrated than stars
o Galaxies are bight in the middle, dark in outer parts
• Dark matter seems to be roughly in a spherical halo

Front 35

What is dark matter? Two possibilities

Back 35

• 1 faint lumps of “normal” (baryonic) matter eg brown dwarfs, black holes, planets, little things, prunes (ie, little thinks that don’t emilt lights)
o MACHOs- Massive Compact Halo Objects
o However, we don’t think this is it, we can find these things if we look hard enough
• Most likely- Dark Matter is some exotic subatomic particle
WIMPs- weekly interacting massive particles, similar to neutrinos.

Front 36

Groups of galaxies

Back 36

• ~10-50 galaxies
• mostly spirals and dwarfs
• no central concentration of mass
• dwarfs are concentrated around big galaxies
• 2 million light years between Milky way and Andromeda

Front 37

Clusters of galaxies

Back 37

o ~100 members
o roughly spherical
o high central concentration of mass
• typically big galaxy is found at center (usually a giant elliptical)
o don’t find as many spirals, but lots of elliptical and Lenticular galaxies
o typically 10 MLY
o environment helps determine the morphology
o we find in them good evidence for dark matter
o we also learn that there is dark matter between galaxies

Front 38

Superclusters of galaxies

Back 38

o filamentary
o Where they intersect we see clusters and groups
o ~100 Million LY
o in spaces between, there are voids, where the density is really low

Front 39

To what scale is the universe not uniform?

Back 39

• The universe is not uniform on smaller scales of <100 MLY. At 14 Billion light years, the universe begins to look rather smooth

Front 40

Interacting galaxies

Back 40

• they are in and interesting and important stage of evolution
• they can merge, form a messy system but over time settles down and to form a different, larger galaxy. Usually you get an elliptical, or a spiral with a bigger bulge.
• These interactions change the types of galaxies
o Cluster spirals and dwarfs, Over time, they interact and orbit with each other, and at a later time then some of the galaxies merge, super giant elliptical.

Front 41

What will happen when the Milky Way collides with the Andromeda Galaxy?

Back 41

The Sun's orbit will change
• They will make a disorganized system of stars, a starburst is triggered, and elliptical galaxy eventually forms, and the galaxies merge.
o Nothing happens to stars the get flung out

Front 42

Mergers of galaxies

Back 42

• Galaxies are so large that compared to the space between them that they often collide. They must interact
o Stars- orbits get scrambled, and stars tend to make a big bulge or even an elliptical. Disks get partly destroyed.
o Collisions of stars are extremely rare!! Stars are PUNY compared to the space between them. Galaxies are almost empty of solid matter. 100 billion star galaxies can collide with only a few stars colliding
o Total gravitational field from each galaxy deflects the orbits of stars in the other galaxy, which changes the distribution of stars, thereby changing the shape of the galaxy
o Gas- gas clouds fill the volume of a galaxy, so they collide directly and lose energy and settles to form a new disk. Can get compressed and causes lot of new star formation (if there’s a ton of this, its called a starburst)

Front 43

Measuring Mass in Clusters

Back 43

• In order for fast-moving galaxies not to fly away from cluster, there must be enough h Mass M to hold galaxies in the cluster. Total mass is 10x more than the mass in the stars and gas! Therefore, there must be DARK MATTER!
o F = ma = mv^2/R^2 = Fgrav
o Fgrav = GMm/R^2

Front 44

How gravitational lenses work

Back 44

• Amount of bending depends on cluster mass
• Total mass of cluster can be measured from amount of bending
• Not enough stars and gas in a cluster to account to bending → 90% of cluster must be made of dark matter
• Basically, gravity can bend the path of light!! Eisenstein thought so
• so you see the galaxy in several wrong places!
• Clusters of galaxies are very good at doing this. The amount of bending depends on the mass, another good way to find the mass of the cluster

Front 45

Quasars

Back 45

Very distant objects with L = 10^37 J/sec = 10^13 L_sun. But we figured right away that they couldn’t be really big galaxies, because the are was really small, less than 1ly in size

Front 46

• How do we know that quasars are so “small?”

Back 46

Rapid time variability- A key property of quasars is that their brightness varies really fast! Light is variable in time with timescales of 1 year or less. This means that the thing must be less than 1 light year in size. Why? Blob of something 1 light year in size that emits a sudden burst of light

Front 47

How to get so much energy from such a small region? You can’t just take a whole bunch of star and put them in one spot.

Back 47

• What is the source of energy in an AGN
Gravitational! Stuff falling into a very deep gravitational well.
Gravity is an efficient energy source if the gravitational field is very strong
How can a black hole emit lots of energy? It can’t, but stuff falling in can emit lots of energy just before it goes in!

Front 48

Unified Model of an AGN

Back 48

Massive blackhole at the very center
Accretion dist (bright) thermal (BB) emission, optical, x ray emulsion,
Size- light days to light years
Jets- sometimes come out of the middle of them. Jets, powered by non thermal radiation. Move really fast, close to the speed of light, v is comparable to c. Jets connect out to radial lobes, whose size can be a million light years! Beyond the extend of stars!
BUT not all AGNs have these parts. For example, a lot don’t have jets.
It can look different from different angles!!! If jet is aimed right toward you, it can appear much brighter, and have a relativistic effect.
Sometimes dust around the center can obscure the accretion disk

Front 49

Types of AGN and their host galaxies.

Back 49

• Quasars- highest luminosities, bright at optical wavelengths.
• What kind of galaxies? Quasars are like ours with interaction
• Interactions trigger AGN (nuclear)activity. Nuclei of some unknown galaxy plays a part. With some fuel, it is kicked to the vicinity of the black hole.
• All massive galaxies have supermassive black holes at their center, but you can only see the AGN if the black hole is being fed.
o Radio galaxies- have jets and groves, but don’t have an optical wavelength, (not much concentration in the disk)
o Blazars- jet is shot right towards us, like Radios but the jet is viewed end on.
o Seyfert galaxies- lower luminosities four in lower luminosity than in spirals.
• Red- radio emission from relativistic particles in radiation

Front 50

Radio emission AGN

Back 50

-Electromagnetic radiation not like blackbody radiation
-Looks similar to the other spectrum, peaks in a color. But the radiation gets and lobes have a shorter, steeper slope! Produced in a different way
-Whenever you accelerate a charged particle, you produce a photon
-Synchrotron radiation
-Electrons spiraling around a coiled magnetic field. Because it is rotating, it emits photons, shows that the stuff is close to the speed of light

Front 51

Blackbody vs. Synchrotron radiation

Back 51

• Blackbodies- electrons accelerated by colliding w/ other charged particles, speeds about speed of light
• Synchrotron - surrounded by electromagnetic field , accelerateed by magnetic fields, speeds “fast”

Front 52

superluminal motion

Back 52

• Series of pictures show that the blobs in jets appear to move faster than the speed of light, blobs moved over 200 light years in 8- years. Impossible! Shift is NOT a actually moving faster than the speed of light. This is an obtical illusion, caused by stuff moving at nearly the speed of light, and right toward you. So how does a whole blob of stuff move at nearly the speed of light? The universe can do it, in the vicinity of massive black holes!!
• What is clear evidence that an AGN contains a black hole? Fast orbital motions indicating a lot of mass in a small space

Front 53

Black hole

Back 53

• Any object whose escape speed is greater than the speed of light.

Front 54

Escape speed

Back 54

How do you throw a rock so that it never returns to earth? How fast does it have to be moving to “just escape?”
• Escape speed from surface of the earth = 7miles/second, Orbital speed= 5 miles/second

Front 55

• The sun suddenly turns into a black hole. What happened to the earth?

Back 55

o The earth stay in the same orbit! BLACK HOLES DON’T SUCK THAT MUCH! You only get sucked in if you’re like within 10 Schwarzschild radius

Front 56

What is the principle of the size of a black hole?

Back 56

• In principle, anything of any mass can be a black hole if in satisfies that Schwarzschild radius.
o If the sun was a blackhole, with 2*10^33gm, radius 3 km!!
o Blackhole at the center of the galaxy, around 10^6 M_sun, must be 3 * 10^6
o Person- 80kg, 10^25m, 10^9 times small than a proton
In reality, only things with very big masses become black holes

Front 57

Classical physics of Newton (in contrast to Einstein)

Back 57

• According to the classical physics of Newton, space is fixed and uniform and time passes at an unchanging rate.
• Example 2: rockship moving at Vrocket = .5c. I shoot laxer at stop sigh. Vl(aser) = 1c. Laser blast hits the stop sign at…
-Newton says this is 1.5C.
-Einstein says is is c, and he is right! Weird but true!!

Front 58

Basic ideas of Special relativity

Back 58

o First principle: the laws of physics are the same for all observers as long as they are moving at constant velocities
o Second principle: regardless of your speed or direction of motion, you will always measure the speed of light to be the same
o Consequently, space and time cannot be thought of as separate entities - they are intrinsically linked

Front 59

Length contraction

Back 59

a stick has a length L when at rest. When moving, at velocity V, it has a shorter length. L = Lo squareroot (1- (v^2)/(C^2))

Front 60

Time dilation

Back 60

 You at rest on Earth. Friend flying past you at high speed V.
• According to you: interval between your heartbeats is t_0= 1 second
• According to your friend the interval between her heartbeats is the same.
• You measure interval between her heartbeats as t= t_0/(squareroot 1- (v^2)/(C^2). You measure a longer time.
o Ex, v = .99c t = 7 seconds

Front 61

Relativistic Increase in Mass

Back 61

• As v → c, mass → infinity
• As V increases, you need a larger and larger force in order to accelerate it.
o An infinite force would be required to get mass moving v = c
• Therefore, particles of matter cannot move at the speed of light

Front 62

Twin paradox

Back 62

• One twin gets on a rocketship and goes away at relativistic speeds. The twin that took the trip returns younger. Ahhh!!
• What “breaks the symmetry” between you and your twin, that allows the twin to be much younger than you on return?
o Twin accelerated at start and end, whereas you did not.
• Special relativity only works at constant velocities! If something is accelerating, we need more than special relativity! We need general relativity! Clock example, clock that goes on a plane is younger.

Front 63

Equivalence Principe

Back 63

• No way to locale distinguish between gravity and acceleration.
• Objects of two different masses accelerate the same!
o All objects in a gravitational field accelerate a the same rate, independent of their mass.

Front 64

Basic Ideas of General Relativity

Back 64

• The mass of an object alters the properties o space and time around it.
• Gravity causes space to curve and time to slow down
• Gets rid of an idea of the “force of gravity”
• Rather, gravity is curved spacetime.

Front 65

General Relativity and the bending of light

Back 65

• principle equivalence implies that gravity can bend light.
• Since acceleration can cause the path of light to appear curved, then, by the principle of equivalence, gravity must also cause light path to appear curved. Observations show that this happens!! Newton could not explain this.

Front 66

Some proof of Einstein's theories of relativity

Back 66

• Deflection of starlight by masses
o Star’s aren’t in the right position during an eclipse.
• Gravitational lensing- basically the same thing, path of light gets bent
• Precession of Mercury’s orbit
• Gravitational time delay- time passes more slowly in a gravitational felid, the strong the field the slower it is
• Gravitational time delay- radio signals from the mars rover were delayed by the sun
• Muons live longer if they are going fast!

Front 67

Structure of a black hole

Back 67

Singularity- all the mass of a black hole is crushed to very small volume, perhaps infinite density at singularity

-Event horizon- Horizon beyond which nothing (including light) can escape. We have no way of learning anything about events, physical processes, etc, that occur beyond the event horizon

Front 68

Three properties of black holes

Back 68

• Mass
• Eclectic charge- actually neutral, but theoretical charged. Big thing with a big charge will attract opposite charge and become neutral
• Spin or angular momentum- Jets come from accretion hole, not from the disk
• How do you avoid being sucked in to a black hole? Go into orbit!! Not anti gravity, that doesn’t exist.

Front 69

• How do you measure the mass of a black hole?

Back 69

o You can measure the period and the radius of your orbit and then use Newton’s for of Kepler’s 3rd law, as long as you are a few AU from the event horizon. General relativity would give you the exact same answer.

Front 70

General Relativity & Curvature of space

Back 70

• Rolling balls on a curves sheet follow trajectories similar to those of things (masses and mass-less things) in curved space.
• What determines the trajectory’s orbit? How the sheet (or space) is curved by masses, Speed of things, And it doesn’t depend on the masses of things being moved around!
• The well becomes deeper as whatever it is become denser.
• Strength of gravity is the same outside the area it effects, it is different in the hole. Effects of relativity become important when the wells of the gravity wall are steep (IE if the object is very very dense)

Front 71

Tidal forces

Back 71

Differential gravity forces. The difference in gravitational force on different parts of the object.

-if you fell into a black hole, this would rip your head off, your legs down, and squish your middle. Stronger gravity at your feet, closer to the black hole. Spaghettification.
-Think of being tied between two cars, going the same direction, but two different speeds, you will get stretched out!!

Front 72

Strength of the tidal forces just outside the event horizon depends on mass of black hole

Back 72

• Stellar mass black hole → tidal forces are strong. Much bigger difference between your feet and your head
• Supermassive black hole- tidal forces are weak. Relative difference between feet, head and center of the black hole is much smaller!! So you don’t get ripped apart, tidal forces wouldn’t kill you.

Front 73

I drop my friend Luke into a black hole. Will I ever see him pass the event horizon?

Back 73

• Because time slows down near black holes!! There is a gravitational time dilation, similar to that which occurs in special relativity. Clocks run slow in gravitational fields, even in the earth. Effect becomes really large when gravity is really strong, like at the event horizon of a black holes. There, it becomes infinite. Time begins to stop. You see a frozen image of Luke, forever!!! However, Luke HAS gone through, he doesn’t see time slow down.
o So what does Luke see when he goes through the black hole?

Front 74

So what does Luke see when he goes through the black hole?

Back 74

• The view of the outside world changes only slightly, and there is no clue that you have actually fallen through the horizon. You can still see the outside universe, you’ll still see photons. The image would be very faint, plus they would be redshifted. Might be in radio. Eventually, the rate of photons would diminish. You would see images of other people as well.

Front 75

Different kinds of black holes

Back 75

Stellar M to 30 M_sun- They’re are nearby, in our galaxy! From the collapsed cores of the most massive star. There could be millions in our galaxy alone, because every large star becomes one. We’ve detected 10 of them.
• Galactic (supermassive) million-billion M_sun
Form from mergers of stellar mass black holes. You need high densities, like the center or galaxies. Galaxies have one or two of these (two if there was a merger).
• Medium Mass black holes, between the two masses probably exist. Mini-holes may or may not exist.

Front 76

How do we see black holes, or know that they are there?

Back 76

• Stuff falling into a black hole heats up and emits a lot of radiation before it falls in
• Gravitational effects on nearby objects, Stars orbiting something massive and dark
o Gravitational lensing
o Easiest way to see are those in binary star systems, where mass from the stars is getting pulled into the black hole
o If a star gets close enough to be ripped apart by tidal forces, the disk gets lit up, which we can detect, and maybe even form a jet
o Remember, black holes don’t always need to have a disk!

Front 77

Significance of Hubble Law

Back 77

It was Hubble who discovered that the universe was expanding.
Hubble “constant” = Ho= 71 km/(s Mpc)
-says the farther away a galaxy is from us, the faster it expanding away from us
• We can use it to get distances to galaxies, but this relation only holds for galaxies at intermediate distances

Front 78

Cosmological redshift

Back 78

o interpret as recession speed using Doppler formula
this is what the Hubble Law is basically measuring

Front 79

Doppler shift versus cosmological redshift

Back 79

Doppler shift- Caused by object’s motion through space
Cosmological redshift- caused by expansion of space, carries galaxies with it. photons are stretched out to longer wavelengths as the space in the universe expands. photon going from one galaxy to the next, by the time it gets to B the universe has stretched out. Think of the rubber band analogy.

Front 80

Chocolate chip muffin analogy of expanding universe

Back 80

There is no special place in the muffin, just like the universe on large scales. Distance between chips before baking is whatever. This grows after baking. X, 2x → 3x, 6x.
Expansion velocity between A, B. 3X-x/t 2x-t. Conclusion, zx is further away, t has receded from A2x as rapidly
• Also, there is no special chocolate chip. Any other one would see the galaxies expanding away from it. Okay, we don’t see any special place in the universe.
• Think of the balloon, not center and no edge. Put galaxy stickers on the balloon. The galaxies themselves don’t expand.

Front 81

The expansion of the universe takes place where...?

Back 81

primarily in the huge voids between clusters of galaxies, “small” objects like galaxies or Earth do not.

Front 82

• What is it that keeps localized regions of space, planetary systems, star clusters, and galaxies, from participation in the general expansion of the universe?

Back 82

o Their mutual or self gravity
o So does gravity overcome the force of the hubble flow? Yeah

Front 83

Why doesn't the Hubble law work for the nearest ( D < 20 Mpc) and the most distant galaxies (Z > .01, D > 400 Mpc)

Back 83

For nearest- motions through space due to gravitational attraction are greater than the hubble flow

For farthest- relativistic effects make relationship between observed reshift and distance more complicated.• Hubble “constant” not the same for galaxies at large distances. Since expansion rate varies with time, so Hubble “constant” not constant. Ho is present value of expansion in the universe

Front 84

Fate of the universe

Back 84

P_crit = = 9.5 * 10^ -27 kgm ^ -3
P_m = = 2.6 * 10^27 kg m^-3
(Bayronic 10%, Dark Matter 90%)
Add Λ and it proves there definitely isn't enough mass in the universe to make it recollapse. Universe will expand forever. Ωm < 1 and Λ > 0

Front 85

How old is the universe

Back 85

Without factoring in gravity to slow down expansion and Λ to speed it up, we get 14 billion years. (basically just the inverse of the Hubble constant)

Factoring in gravity and Λ, we get 13.7 +/- .5 billions years, this is our best estimate.

Front 86

Evidence that the universe has evolved over time (or evidence of the big bang)

Back 86

expansion of the universe, the night sky is dark, most quasars and most star formation is at red shifts between 2 and 4. This was a period of great activity, less goes on in today’s universe. Cosmic background radiation. Photons which come from every direction, almost the same intensity from every location in the sky. Radiation left over from very early universe, leftover glow from big bang. Relic from a hotter, denser universe.

Front 87

How do we measure cosmological distance and time?

Back 87

We don’t have any direct distance measurements for z > 1; Type Ia supernovae can be seen beyond z > 1. But they don’t go off in every galaxy of quasar. What we observe is the cosmological redshift

Not so simple to relate this to a distance, because you need to know the “cosmological parameters.” What we need to know is everything about the universe
• Expansion of rate Ho
• amount of mass in the universe acting to decelerate the expansion
• amount of ark energy

Front 88

What did the universe look like at very high z?

Back 88

The universe looks different at high z. Galaxies are high z mean more irregular. Quasars more common than today. We think that every galaxy has a super massive black hole in the center. Fever later the gas goes away and the SMBH lights the sky up, we see it as an AGN, especially quasars. This happened a lot more frequently in the early universe, when galaxies were merging, galaxies mergers move towards gas and merge towards centers. When subermassive hole is not being fed, NO AGN with saturation most galaxies as in nearby universe. Lots of supermassive black holes, but very little feeding, very few AGN. Peak of star formation peaks with quasars.

Front 89

Olber’s paradox: why is the sky dark at night?

Back 89

The Newtonian universe is infinite in space, and infinitely old and uniformly filled with stars. In this universe, night sky would be as the sun or the surface of. This would be bad, then the temperature in space would be equal to temperature of the sun. Because every line of sight would interrupt a star, like a forest, if you’re in the middle you can’t see out, because every line of sight is interrupted.

Sky is dark due to cosmic light horizon- there hasn't been enough time for some light to reach us. Presently distance to CLH is 13.7 BLy, gets bigger all the time.

Front 90

How can galaxies exist beyond the CLH< if it is 13.7 billion years away, and the inverse is only 13.7 billion years old?

Back 90

• Because space can expand faster than the speed of light! Nothing can move through space faster than light. But relativity says distant regions of space can move faster than the speed of light.

Front 91

Cosmic Microwave Background radiation

Back 91

-2.7 degree K cosmic microwave background radiation field
*-• Spectrum of a nearly perfect blackbody, most perfect that has ever been measured, never seen before. Peaks in the radio part of the spectrum, λ= 1.1mm. Temperature of 2.725 K.
-*• Isotropy of the cosmic microwave background. Nearly the same I every single direction. Intensity of photons nearly the same in all directions. This means all of space experienced the big bang. Formed long before stars and galaxies existed.

Front 92

I thought that the big Bang was hot! If the cosmic microwave background radiation is the radiation left over from the ig band, when did the universe cool down to about 3K?

Back 92

• Just recently!! The universe used to be several thousand degrees. As they have traveled and been stretched out by a factor of 1000 they became cooler because of the expansion of space.
Now the are 2.7 K, when they were produced they were ~ 3000 K.

Front 93

How do cosmic photons interact with matter?

Back 93

Today they don't. But in the past, the CMB photons had more energy & shorter wavelengths, and thus at some point in the past must have had enough energy to ionize atoms. After some expansion, the cosmic photons could travel without being absorbed. This transition from opaque → transparent to CMB is called “era of recombination-" 380,000 years after the big bang. From this we can set z to something, because we know that at that time z was 1100.

Front 94

What was the universe like before z > 1100?

Back 94

Filled with high energy photons reacting vigorously with Ps and ex. Matter is in the form of plasma. Atoms can form but are quickly destroyed (ionized) by cosmic photons.

Front 95

If the universe if full of microwave radiation, why isn’t it cooking?

Back 95

The intensity is must higher in a microwave oven. Also it is a very tiny spectrum in a microwave oven. Microwaves interact with molecules in food but not atoms and the universe is mostly atoms

Front 96

Dipole Anisotorpy in the CMB

Back 96

When you subtract 99.9% of the average signal, you get a dipole pattern
In graph form, with the lowest 90% of the range removed, as opposed to the whole scale, you get this. Keep removing 90%, three times, (temperature ranging from 2.7366 to 2.732) a tiny scale, you get a sine curve. 1/1000th of the scale shows you this. • This pattern is a Doppler shift. Its caused by the rotation of the earth with respect to the cosmic background. Moves sinyonsoitally.

Front 97

So why are we moving with respect to the CMB?

Back 97

Gravitational pull on earth and milky way from various “local” sources. So net motion is 370 km/s towards Leo (in between Virgo and Great Attractor). The Great Attractor is the largest supercluster in the region

Front 98

The Second Antisotrophy- Small scale fluctuations in CMB

Back 98

This is with 99.999% removed. If dipole and Milky War artifacts are subtracted from CMB map small fluctuations remain. Small λ shifts in the CMB spectrum from one spot to another. Correspond to small temperature differences. ΔT/T ~ 6*10^-6 (difference between the hottest and coldest spots on the maps). Shows the seeds of structure in the universe, like a baby picture.

Front 99

•How and when did structure form in the universe?

Back 99

Now, matter distribution in the universe is very lumpy! There are places in the universe that are much denser than the average density (10^4 H atom m^3). Lumps didn’t form before recombination because cosmic radiation was coupled to matter, preventing lumps from cooling, until z = 1000.

Front 100

How does a lump of matter form from gravity?

Back 100

If you have lump of matter which has collected by its self gravity (like Earth) it would take a LOT of energy to disassemble it, because you’d have to fight against gravity to do it. Think of the reverse situation. Pieces of matter being pulled together by self-gravity by conservation of energy, energy must be released when this happens. If energy can’t be released, then the lump can’t collapse. Energy is released by photons. If photons can get out, thing can collapse (after decoupling.) But if photons can’t get out, the thing can’t collapse (before decoupling).

Front 101

How do we know that the dipole signal in the CMB is a Doppler shift and the small-scale fluctuations are temperature differences?

Back 101

The spectra. For the dipole, we see two blackbody curves, one redshifted and one blueshifted. Two blackbody curves, on top of another, hot spots versus cool curves. These never cross, one is just a higher temperature blackbody curve.

Front 102

How far could the fastest signal go during the entire history of the universe up to that point?

Back 102

D = ct
D is the cosmic light horizon, t = age of the universe
At age of 380,000 years, the size of the cosmic light horizon and the size of the largest causally connected region (regions which were close enough to influence each other, if something physical like a signal could go from one spot to another). So we think that the biggest blobs in the CMB fluctuations are probably ~ 380,000 Ly in size.

Front 103

So how big does this appear if space is flat?

Back 103

If space is flat, blobs are 1° in angular size. But what we actually see…Biggest blobs are 1°!!
This strongly suggests that space in the universe is flat or nearly flat. They aren’t smaller than 1°, if so we would be in hyperbolic space. Its not larger than 1°, which would be a spherical space.

Front 104

• What is dark energy?

Back 104

The mass-energy needed to bridge the gap between the mass we know exists and what is needed to make the universe flat. It is causing the expansion to accelerate.

Front 105

Curvature of Space + Dark Energy

Back 105

Contents of the universe determines its curvature. Total amount of matter, radiation and dark energy
Rho_o = Rho m + Rho rad + Rho dark energy ← total density
• Ω_m= ρ_m/ρcrit
• Ωrad = ρ_rad/ρcrit
• Ω_Λ= ρ_Λ/ρcrit
• Ω_o = Ω_m + Ω _ rad + Ω_Λ
Ω_o ~ 1, and we know Ω_m = .27 and Ω_rad = .00005so we know that to make up the difference, Ω_Λ = .73!!!! IE, dark energy must exist, and there is more of it than mass and energy in the universe.

Front 106

Other evidence for Dark Energy

Back 106

-Acceleration of the expansion rate from measuring distance versus redshift of Type Ia supernovae
-Data shows the expansion is speeding up- data basically fits the red line. There’s been les expansion in the past, now its accelerating. We don’t understand it, but we’re calling it dark energy.

Front 107

Contents of the universe

Back 107

73% is dark energy
27% is matter
23% is dark matter
4% is baryonic (the stuff we sense)
baryonic in galaxies – 1% of the total
baryonic outside galaxies- 3% (← not yet detected)

Front 108

What do CMB photons tell us about the universe?

Back 108

the universe was once 10^9 denser and 10^3 hotter

Front 109

The Origins of the light elements

Back 109

-Some were formed in the very early universe
-Evidence that the universe was once 10^9 degrees hotter
-Tells us how much is DARK matter and how much is baryonic matter

Front 110

At t = 1-5 minutes after the Big Bang...

Back 110

T = 10^9 degrees – hot enough for nuclear reactions to occur – fusion
If it ever was this hot then we expect nuclear reactions to have occurred
BUT – would the atoms have existed?
At this time Hydrogen nuclei underwent nuclear reactions to form slightly heavier elements
Hydrogen fused to form deuterium (1), Helium (2), Lithium (3), Beryllium (4), Boron (5)
Not made in stars, but mostly in the BB

Front 111

So what is different about stars and the early universe? How are conditions in the early universe different that the conditions in the core of a star?

Back 111

Same temperatures and densities – but existing for DIFFERENT lengths of times
T=1-5 minutes vs. Stars existing for billions of years… Exactly like cooking – what you get out of cooking depends on how long you cook it – So temps and densities similar to the core of stars. The difference is the amount of time w/ the conditions suitable for fusion
o Stars – millions of years for light elements to be fused into heavier elements
o Early universe – only a few minutes – not enough time for light elements to be cooked.
Also = there are too much of the light elements to be explained by making them in stars.

Front 112

So what do the number of relative light elements in the early universe tell us?

Back 112

What we measure is the relative number of light elements which tells us the density of baryonic normal matter at the time when the universe was hot enough to fuse

Front 113

Density of the early universe- what would happen if it had been higher or lower?

Back 113

-If HIGHER – than more collisions - = more heavy elements
-If LOWER – than fewer collisions = less heavy elements

Front 114

So the very early universe had what kind of density?

Back 114

So we know that the EARLY universe has 4% of the critical density in the form of atoms
-Ratios of light elements means that the universe was 1027 denser and 109 hotter

Front 115

Inflation

Back 115

A brief period of superfast expansion hypothesized to occur a fraction of a second after the BB. Tries to solve horizon and flatness problems.
-The universe expanded by a factor of 10^50 in the time of 10^-32 seconds. Before this happened all regions of the universe were in causal contact.

Front 116

Horizon problem

Back 116

HOW CAN YOU HAVE very distant regions of space have very nearly identical temperatures? THEY ARE NOT WITHIN causal contact with each other…A is outside the Cosmic Light Horizon of B and it would seem that A and B could never have been in causal contact with one another.
In order to get something to be the same temperature they have to be touching… Things must be in contact with one another.

Front 117

The Flatness Problem

Back 117

WHY DOES the universe now appear so flat?
-If start with Omega being 0.9999 ( a little different from 1) – as the universe expands – it will be very different from 1
-This means that if it is 1 now
-Then it had to be EXTREMELY near 1 in the early universe
-OR maybe inflation happened which would flatten stuff out
-Can be understood if the universe expanded ENORMOUSLY at early times so much that the observable universe appears flat.

Front 118

Flatness problem and the Cosmic Light Horizon

Back 118

If the universe fit within our CLH(bracelet) - Within our CLH – we can tell if universe was curved
-WELL – what if the region of the universe is bigger ( basketball) - much harder to tell;
-WELL - if the earth represented the entire universe and we are still using our bracelet – you would see the flatness
-OUR PATCH is so small compared to the universe… the universe is much, much bigger than our CLH.
Likewise, Omega =1 is for our light horizon, could be a bit different.

Front 119

Evidence for the big bang, in sum

Back 119

1.) Expansion of the universe
2.) CMB – evidence for the big Bang – that it was once a billion times denser
3.) Abundance of the light elements – the universe was once hot enough to undergo fusion everywhere – distinct stages in the evolution of the universe

Front 120

Big Bang Theory

Back 120

1.) Big bang theory describes HOW our universe is evolving, not how it began…. (Jim Peebles)

Making the point that – the BB can refer to the evolution of the universe – but what happened after the beginning…

This is what we have evidence of

Front 121

Standard Theory

Back 121

2.) The standard cosmological model for the beginning of four things: SPACE, TIME, ENERGY and MATTER
Not matter exploding into preexistent space

But an explosion of space and time with energy and matter - all originating at the same process

Front 122

Questions we can't answer

Back 122

How large is the universe?
Are there multiverses?
Is the universe finite or infinite? Which one is better? If the three dimensions of space are curved back on itself – into a fourth dimension is that dimension finite or infinite
What existed before the BB? We are masters of space but prisoners of time… is it only cause we are finite Time is more bizarre – limited brains?
What caused the BB? Maybe we are one of many universes…. Perhaps someday we will learn more about this
THERE WILL ALWAYS be the QUESTION of the ULTIMATE CAUSE – outside the universe

Front 123

Quasar F (for Far) has the same luminosity as Quasar N (for Near), But F is 10 times further away.
a) N appears 10 times brighter than F.
b) N appears 100 times brighter than F.
c) F appears 10 times brighter than N.
d) F appears 100 times brighter than N.
e) F appears to have the same brightness as N.

Back 123

b) N appears 100 times brighter than F.

Front 124

2) What is the best way to stop being pulled into a black hole?
A. Fire rockets continuously.
B. Invent anti-gravity.
C. Go into orbit, rely on centrifugal force.
D. Reduce the mass of the ship by throwing almost everything overboard.
E. Fall into the black hole and get frozen at its horizon.

Back 124

C. Go into orbit, rely on centrifugal force.

Front 125

What is actually located at the event horizon of a black hole?
A. Nothing
B. an infinitely dense concentration of mass
C. The outer boundary of a wormhole
D. a sphere of photons
E. The remnant of the star that collapsed to the black hole.

Back 125

a) Nothing

Front 126

Suppose that there is galaxy whose present distance from us is 20 billion light years. If the universe is presently 14 billion years old
a) we will never be able to observe it.
b) the light we receive from it now was emitted in the early universe.
c) we cannot observe it now, but we may be able to observe it
in several billion years
d) it is within our cosmic event horizon
e) whether we observe it now depends on the values of the hubble constant and omega

Back 126

c) we cannot observe it now, but we may be able to observe it in several billion years

Front 127

5) Because of the general expansion of space, all distant galaxies appear to be moving away from us, with speeds that increase with distance from our galaxy. An observer in one of these distant galaxies would apparently see
a) all galaxies on one side of the observer moving toward
her and all galaxies on the other side moving away from her;
the more distant the galaxy, the faster its motion.
b) all galaxies moving away from her, the more distant galaxies
moving faster.
c) all galaxies moving away from her, with closer galaxies
moving faster.
d) all galaxies moving toward her, with more distant galaxies
moving faster.

Back 127

b) all galaxies moving away from her, the more distant galaxies moving faster.

Front 128

6). The average temperature of Mars is lower than that of Earth. If a distant observer measures the infrared radiation from both Mars and Earth, then
A. the emission from the two planets will peak at the same wavelength, but that from Mars will be less intense than that from Earth.
B the wavelength of peak emission from Earth will be longer than that from Mars.
C. the wavelength of peak emission from Mars will be longer than that from Earth.
D. it is not possible to predict the behavior of the radiation from the information given.

Back 128

C. the wavelength of peak emission from Mars will be longer than that from Earth.

Front 129

7) I thought that the Big Bang was hot! If the cosmic microwave background radiation is the radiation left over from the Big Bang, why then is it only 3K?

A .It is not directly from the Big Bang itself. It is from cold, intergalactic hydrogen clouds that are left over from the Big Bang.
B. The Big Bang itself was hot, but by the time the universe became transparent the temperature had already decreased to 3 K.
C. The Big Bang itself was hot, but the temperature decreased as the universe
expanded, and the temperature now is 3 K.
D. Big Bang was not hot! Its temperature was the same as we observe it now from the cosmic background radiation.

Back 129

C. The Big Bang itself was hot, but the temperature decreased as the universe

Front 130

8) The expansion of the universe takes place:
A. only between objects separated by a near vacuum; as a result, our bodies do not expand but the Earth-Moon system does.
B. primarily in the huge voids between clusters of galaxies: "small" objects like galaxies or the Earth do not expand.
C. only over distances about the size of a galaxy or larger; consequently, our galaxy expands but the solar system does not.
D. between all objects, even between atoms in our bodies, although the expansion of a person is too small to be measured reliably

Back 130

B. primarily in the huge voids between clusters of galaxies: "small" objects like galaxies or the Earth do not expand.

Front 131

9)What major problem would arise if Hubble's constant turned
out to be 100 km s-1 Mpc-1
A. Some galaxies would be farther away than the edge of the universe.
B. Galaxies would have had to have traveled faster than our observation indicate.
C. Galaxies would be traveling too fast for the universe to be gravitationally bound.
D. The age of the universe would be less than the ages of some of the stars in it.

Back 131

d) The age of the universe would be less than the ages of some of the stars in it.

Front 132

Compared to the present day
Milky Way, the galaxy 3 billion
years ago would have had
1. More stars in the halo
2. More gas in the disk
3. More stars in the disk
4. More stars in the bulge
5. More time alone

Back 132

2. More gas in the disk

Front 133

Most stars in a disk
1. Stay inside spiral arms
2. Travel in radial (in & out)
orbits in the disk plane
3. Have random orbits and
spend most time in the disk
4. Travel in circular orbits in
the disk plane
5. Travel in nearly circular
orbits close to the disk plane
6. Have about the same age

Back 133

4. Travel in circular orbits in
the disk plane

Front 134

How can we see Gas in the
universe?

1. It emits photons
2. Light from stars is doppler shifted by gas particles
3. By its gravitational effect on
nearby stars
4. Via the rotation curves of
galaxies
5. You can’t see gas, you smell it

Back 134

1. It emits photons

Front 135

Why are the outer parts of most
spiral galaxies gas-rich?

1. Gas is blown outwards by lots
of supernovae during starburst
phase of evolution
2. Stars don’t form so easily in
the gas of the outer galaxy
3. The gravitational force on the
small gas particles is weak
4. Magnetic fields keep the gas
from settling to center
5. Gas is bound to the Dark
Matter

Back 135

2. Stars don’t form so easily in
the gas of the outer galaxy (lower gas density in the outer parts of the galaxy)

Front 136

Eddie is stopped for going through a
red light in his Hummer. He tells the
cop that the Doppler effect caused
the red light to appear green.
How fast would he need to be going?
1. 200 mph
2. 100 km/sec
3. 1% of speed of light
4. 33% of speed of light
5. 99% of speed of light

Back 136

4. 33% of speed of light

Front 137

The mass of our galaxy is best found by:

1. Estimating the number of stars in
the northern & southern skies
2. Radio telescope measurements of the amount of interstellar
hydrogen
3. Measuring how fast the galaxy
rotates
4. Measuring how fast the galaxy
expands at large distances from
the center
5. Just looking at it

Back 137

3. Measuring how fast the galaxy
rotates

Front 138

How can astronomers measure
the rotational speed of a galaxy?

1. From a time series of galaxy images
taken over many years
2. From the difference in the Doppler
shift from one side of the galaxy to
the other
3.From the motion of the galaxy with
respect to the background
universe
4. By measuring the changing
curvature of the spiral arms
5. From the change in periods of
Cepheid variables across the galaxy

Back 138

2. From the difference in the Doppler
shift from one side of the galaxy to
the other

Front 139

Why are the effects of Dark Matter
felt on scales of galaxies but not
within the classroom?

1. There is no dark matter in the classroom
2. The atmosphere shields most of the dark matter particles from earth’s surface
3.The density of dark matter relative to normal matter is low in the room but not in the galaxy
4. They ARE felt in classroom but we are used to it so don’t notice it (like
atmospheric pressure)
5. I can feel it. What’s wrong with you?

Back 139

The density of dark matter relative to normal matter is low in the room but not in the galaxy

Front 140

How are galaxies
distributed in space?

Back 140

• On smaller scales (up to 100 MLY)
we can identify individual coherent
structures such as groups, clusters,
superclusters

On large enough scales (>1 BLY) the universe appears uniform to us

Front 141

What will happen to the Sun
when the Milky Way collides with
the Andromeda Galaxy (M31)

1. It will collide with a star
from M31
2. It will collide with a star
from the Milky Way
3. It will get pulled into the
central black hole
4. It will be ejected into
intergalactic space
5. Its orbit will change

Back 141

5. Its orbit will change

Front 142

What things will happen when the Milky Way collides with the Andromeda spiral Galaxy?

1. They make a disorganized system of stars
2. A starburst is triggered
3. An elliptical galaxy eventually forms
4. Stellar collisions trigger numerous
supernovae
5. The galaxies merge
6. All but 4

Back 142

6. All but 4

Front 143

Major merger sequence

Back 143

Early: disks well separated, disturbed but not totally disrupted

Intermediate: distinct nuclei embedded in common envelope

Late: tidal arms emerging from single nucleus, surrounded by mostly relaxed stellar distribution

Front 144

How do we know that quasars are
so “small”?

1. Rapid Time variability
2. Measurements of angular diameter and distance
3. Applying the small angle formula
4. Using parallax techniques
5. We don’t know this, we assume it

Back 144

1. Rapid Time variability

Front 145

What is the source of energy
in an AGN?

1. Chemical
2. Solar
3. Nuclear fission
4. Nuclear fusion
5. Electromagnetic
6. Gravitational
7. Matter – anti-matter annihilation

Back 145

6. Gravitational

Front 146

How can a black hole emit lots of
energy?

1. It can’t, but some stuff falling
TOWARD the black hole gets
shot outwards
2. Energy can go into 1 black hole
and out another, via a wormhole.
3. It can by the process of
Hawking radiation
4. It can’t, but stuff falling in can
emit lots of energy just before
it goes in

Back 146

4. It can’t, but stuff falling in can
emit lots of energy just before
it goes in

Front 147

What is clear evidence that an
AGN contains a black hole?

1. Fast orbital motions
indicating a lot of mass in a small space
2. Prodigious luminosity
3. Non-stellar spectrum
4. Relativistic jets
5. Gravitational lensing
6. The textbook

Back 147

1. Fast orbital motions
indicating a lot of mass in a small space

Front 148

During the merger of our Galaxy
with M31, which way are we most
likely to die?

1. Colliding with star or planet
2. Falling into supermassive black hole at nucleus
3. Blasted by AGN jets from black
hole
4. Sun turns into red giant
5. Boredom
6. Bugs

Back 148

1. Colliding with star or planet (very
small chance)
2. Falling into supermassive black hole at nucleus (very small chance)
3. Blasted by AGN jets from black
hole
4. Sun turns into red giant
5. Boredom
6. Bugs

Front 149

How do you throw a rock so that it
never returns to earth (ie. escapes)?

1. Throw it fast enough
2. Give it enough acceleration
3. Get it moving at a high enough
speed, the speed depends on the
mass of the rock
4. Throw it high enough to get it
beyond the influence of earth’s
gravity
5. It’s not possible, because rocks
have no internal thrusters, unlike rockets

Back 149

1. Throw it fast enough

Front 150

How much weaker is the gravitational force on an astronaut in the International Space Station (ISS), compared to that on earth’s surface?

1. There is no gravity at ISS
2. Gravity is a lot weaker at ISS
3. Gravity is a little bit weaker
at ISS
4. Gravity is the same strength
at ISS
5. Gravity is forbidden at ISS

Back 150

3. Gravity is a little bit weaker
at ISS

Front 151

Will the sun ever turn into a
black hole?

1. No, it’s mass is too low
2. Yes once it evolves past
helium core fusion
3. No, its core will form a
neutron star
4. Yes after it supernovaes
5. Yes but not for another5 billion years

Back 151

1. No, it’s mass is too low

Front 152

The sun suddenly turns into a black
hole. What happens to the earth?

1. Earth gets quickly drawn into the
black hole by gravity
2. Earth gets slowly drawn into the
black hole by gravity
3. Tidal forces rip the earth apart
4. The earth stays in the same orbit
5. The earth’s orbits shrinks but the
earth doesn’t go into the black
hole
6. The black hole eats the earth but
then spits it out again

Back 152

4. The earth stays in the same orbit

Front 153

Train in tunnel paradox

What do people on the train observe?
For them, the train does not fit into
the tunnel... What happens when the
iron gates close? DO THEY DIE?

1. Yes, but not all of them
2. No, length contraction allows the
train to fit between the gates
3. No, since the gates don’t close at
the same time in their view
4. No, because of time dilation
5. Yes, but in a parallel universe an
identical train survives, so it’s OK

Back 153

3. No, since the gates don’t close at
the same time in their view

Front 154

Your twin travels off into space at high speeds and comes back young after you are dead.
What "breaks the symmetry" between you and your twin, that allows the twin to be much younger than you on return?

1. While the physiological effects on your bodies are different, you both have experienced the same passage of time
2. Twin moved through space, whereas you did not
3. Twin accelerated at start and end,
whereas you did not
4. Twin experienced different
gravitational fields on journey.
5. Twin lost track of time during journey

Back 154

3. Twin accelerated at start and end,
whereas you did not

Front 155

Principle of Equivalence

Back 155

There is no way to distinguish between the effects of acceleration and the effects of gravity- they are equivalent!

Front 156

Tests of general relativity

Back 156

1. Deflection of starlight by masses, gravitational lenses
2. Advance of perihelion of Mercury’s
orbit
3. Gravitational time delay: time passes more slowly in stronger gravitational field; radio signals from Viking Spacecraft on Mars were delayed as they passed by the Sun

Front 157

You guide your spacecraft into an orbit a few AU from a black hole. You know its mass is 4 or 5 solar masses, but you want to measure it more precisely. How would you do this?

1. It is impossible to see beyond the
event horizon, so your estimate of 4-5 solar masses is as good as you can do.
2. You can measure the period and the radius of your orbit and then use
Newton's form of Kepler's 3rd Law.
3. You cannot use Newton's form of the Third Law. You must use GR.
4. Move to the event horizon of the black hole. From this distance the mass can be calculated using GR.

Back 157

2. You can measure the period and the radius of your orbit and then use
Newton's form of Kepler's 3rd Law.

Front 158

If you fall into a solar-mass black hole

A. Time will appear to you to slow
to a halt as you enter the
event horizon.
B. You will die, torn apart by tidal
forces (spaghettification)
C. You will die, incinerated by
intensely hot radiation.
D. You will die, crushed at the
central singularity.
E. You will pass through a
wormhole into another part of
the Universe. You will die.

Back 158

B. You will die, torn apart by tidal
forces (spaghettification)

Front 159

Prof K. is investigating a supermassive black hole from a “safe distance”. He decides to drop his friend Luke toward the black hole. Will Prof K. ever see Luke pass the event horizon?

1. Yes, he will see him fall faster and faster until he disappears as he falls through the event horizon.
2. Yes, but light from him will be so
blueshifted that he would need X-ray
eyes to see him.
3. No, he will be tidally compressed to zero thickness and disappear from sight before he reaches the event horizon.
4. No, he will appear to stop and hover forever just above the event horizon.

Back 159

4. No, he will appear to stop and hover forever just above the event horizon.

Front 160

When you fall thru the event
horizon of a Black Hole

A. The view of the outside world disappears, and you find yourself in darkness.
B. The view of the outside world changes only slightly, and there is no clue that you have actually fallen through the horizon.
C. You achieve enlightenment
D. You go through a wormhole of doom

Back 160

B. The view of the outside world changes only slightly, and there is no clue that you have actually fallen through the horizon.

Front 161

Different sizes of Black Holes

Back 161

Stellar M~3-30 Msun
exist! Form from collapsed cores of massive stars

Galactic (Supermassive) M~106-109 Msun exist! Form from mergers of stellar mass BHs

“Medium” M~102-106 Msun
probably exist – not yet “seen”

Mini-holes M<<1 Msun
?????

Front 162

Gravitational time dilation

Back 162

Clocks in gravitational fields run more slowly
Happens in ANY gravitational field!
Effect becomes infinite at event horizon
Related effect: gravitational redshift

Front 163

How do we see Black Holes?

Back 163

The easiest black holes to see are those in binary star systems, where mass from evolving star is pulling onto BH accretion disk

Front 164

For which galaxies would the
linear Hubble relation be
expected to hold?

1. All galaxies
2. Only the nearest galaxies
3. Only the most distant
galaxies
4. Only galaxies at
intermediate distances
5. No galaxies

Back 164

4. Only galaxies at
intermediate distances

Front 165

The expansion of the universe
takes place

1. between all objects, even between atoms in our bodies, although the expansion of a person is too small to be measured reliably.
2. only between objects separated by a near vacuum; as a result, our bodies do not expand but the Earth-Moon system does.
3. only over distances about the size of a galaxy or larger; consequently, our galaxy expands but the solar system does not.
4. primarily in the huge voids between clusters of galaxies: "small" objects like galaxies or the Earth do not expand.

Back 165

4. primarily in the huge voids between clusters of galaxies: "small" objects like galaxies or the Earth do not expand.

Front 166

What is it that keeps localized regions of space, such as planetary systems, star clusters, and whole galaxies, from participating in the general expansion of the universe?

1. pressure from dark energy
2. their mutual or self-gravity
3. gravity from the central object (e.g. the Sun, SuperMassive Black Holes)
4. centrifugal force produced by their
motion around a massive central
object (e.g., the Sun, SMBHs)
5. Electromagnetic attraction of atoms
6. Subatomic stubborness

Back 166

2. their mutual or self-gravity

Front 167

If the Universe is expanding,
what is it expanding into?

1. A higher dimensional space.
2. The future.
3. It is not expanding into anything:
expanding means that the distances between objects (galaxies) in the Universe are increasing with time.
4. The Universe is not actually
expanding: it's just a convenient
way for describing Hubble’s Law
5. We don’t know

Back 167

3. It is not expanding into anything:
expanding means that the distances between objects (galaxies) in the Universe are increasing with time.

Front 168

What determines the Fate of the Universe?

1. the total mass of the universe
2. the average density of matter
3. the average density of dark matter
4. The amount of dark energy
5. The average density of matter and
dark energy
6. the ratio of dark matter to normal
matter
7. What you make of your life after
Yale

Back 168

5. The average density of matter and
dark energy

Front 169

What major problem would arise if
Hubble's constant turned out to be
100 km s-1 Mpc-1

1. Some galaxies would be beyond the cosmic light horizon.
2. Some galaxies would have had to have traveled faster than our observations
indicate.
3. The age of the universe would be less than the ages of some of the stars in it.
4. The age of the universe would be greater than the ages of some of the stars in it.
5. Some galaxies would be traveling too fast for the universe to remain gravitationally bound.

Back 169

3. The age of the universe would be less than the ages of some of the stars in it.

Front 170

How do we know how far away
objects are with z>1?

1. Measure cosmological redshift (z)
2. Measure cosmological redshift z plus Ho, Omega(m), Omega(Lambda)
3. Measure Ho
4. Measure Recession velocity plus Ho
5. Measure brightness of type Ia supernova
6. Measure period and brightness of
cepheid variable

Back 170

2. Measure cosmological redshift z plus Ho, Omega(m), Omega(Lambda)

Front 171

Some z values and times

Back 171

Nearest Quasar : 250x10^6 lt-yrs 250x106 years, z= .02

Further quasar: 12.5x10^9 lt-yrs *12.5x109 years ago, z= 6

CMB photons: 13.3x10^9 lt-years 13.3x10^9 years ago, z= 1100

Big Bang: 13.7x10^9light years, 13.7x10^9 years ago, z= infinite

Front 172

Low z versus high z galaxies

Back 172

Galaxies at high z are more irregular- still forming, less settled.

Galaxies at low z are more regular- mostly formed, mostly settled.

Front 173

Why is the night sky dark?

1. Universe is expanding.
2. Universe is expanding plus relativity effects.
3. Light from objects farther away than a certain distance has not yet reached us.
4. The expanding universe from the Big Bang only extends so far into space because matter can only travel at or below the speed of light.
5. The cosmological redshift has moved the light from very distant objects out of our detectable range.
6. Dust in intergalactic space blocks our view of more distant objects.

Back 173

3. Light from objects farther away than a certain distance has not yet reached us.

Front 174

How can there be galaxies farther than 13.7 BLY away if the CLH is 13.7 BLY away, and the universe is only(!) 13.7 Byr old?

1.because galaxies can move through space at speeds faster than c
2. because space can expand faster than the speed of light
3. because stuff out there was formed by a different, earlier big bang
4. there can be galaxies from another universe out there
5. there is nothing beyond the CLH
6. there is nothing beyond in the CLH now, but there will be in the future

Back 174

2. because space can expand faster than the speed of light

Front 175

I thought that the Big Bang was hot!
If the cosmic microwave background radiation is the radiation left over from the Big Bang, when did the universe cool down to about 3 K?

1. one second after the Big Bang, when electron-positron pair production ceased
2. three minutes after the start of the Big Bang, when primordial nuclear reactions ended
3. 380,000 years after the Big Bang, when the universe became transparent to
radiation
4. 1 Byr after the big bang, after the peak of the quasar era
5. just recently

Back 175

5. just recently

Front 176

A photon with a wavelength of 1
millimeter (10-3 m; radio) encounters a H atom. What happens?

1. Nothing, the photon passes
by
2. The photon is absorbed by
the atom
3. The photon is scattered by
the atom
4. The photon and atom annihilate each other
5. The atom ignores the
photon

Back 176

1. Nothing, the photon passes
by

Front 177

A photon with a wavelength of 0.1
microns (10-7 m; UV) encounters a H atom. What happens?

1. Nothing, the photon passes by
2. The photon is absorbed by the atom
3. The photon is scattered by the atom
4. The photon and atom annihilate each other
5. The atom loves the photon and eats it right up

Back 177

2. The photon is absorbed by the atom

Front 178

Universe before z>1100,
T>3000K, t<380,000 yr (ABB)

Back 178

Filled with high energy photons colliding vigorously with p’s & e’s
• Matter is in the form of plasma (p’s & e’s)
• Atoms can form but are quickly destroyed (ionized) by cosmic photons
• Cosmic photons had enough energy to ionize atoms
• Universe opaque to cosmic photons
• Matter & energy tightly coupled

Front 179

Universe AT z=1100, T=3000K,
t=380,000 yr (ABB)

Back 179

Cosmic photons suddenly no longer have enough energy to ionize atoms (due to expansion)
• p’s & e’s combine to form atoms (not ionized)
• “era of recombination (combination?)
• “era of decoupling” (of matter & cosmic
photons)
•Moment when universe changed from being opaque to transparent (for cosmic photons)
• all cosmic photons we see now were created at this time

Front 180

If the universe is full of microwave radiation, then why does food in a microwave oven heat up, but not food sitting on the countertop?

1. Microwaves can be absorbed by food only if they first reflect off metal surfaces
2. The intensity (density) of microwaves in an oven is much higher than the intensity of the CMB
3. The CMB radiation is much cooler than the microwaves used to cook food.
4. The CMB photons have a much lower velocity (kinetic energy) than microwave photons used to cook food
5. The universe is actually cooking
everything right now!

Back 180

2. The intensity (density) of microwaves in an oven is much higher than the intensity of the CMB

Front 181

If the universe is now transparent to cosmic microwave background radiation, then how come microwaves can heat up my dinner?

1. Microwaves can be absorbed by food only if it is surrounded by air.
2. The intensity (density) of microwaves in an oven is much higher than the intensity of the CMB
3. The CMB radiation is much cooler than the microwaves used to cook food.
4. The CMB photons have a much lower velocity (kinetic energy) than microwave photons used to cook food
5. Microwaves interact with molecules in food but not atoms and the universe is mostly atoms

Back 181

5. Microwaves interact with molecules in food but not atoms and the universe is mostly atoms

Front 182

Why are we moving with regard to the CMB?

1. Rotation of milky way
2. Because we are not at center of universe
3. Gravitational pull on earth and milky way from various “local” sources
4. Our expansion is slowed by gravity but the photon’s expansion is not
5. We just can’t help it –
we just gotta MOVE!!

Back 182

3. Gravitational pull on earth and milky way from various “local” sources

Front 183

Why didn’t lumps of matter form
before recombination?

1. The matter was too hot for
gravity to form lumps
2. Gravity was too weak compared to dark energy
3. Radiation was coupled to matter,
preventing lumps from cooling
4. Radiation was the main source of
mass-energy and gravity until recombination
5. Not enough time for gravity to
form lumps
6. Because Jesus said so!

Back 183

3. Radiation was coupled to matter,
preventing lumps from cooling

Front 184

How do we know that the dipole signal in the CMB is a doppler shift and the small-scale fluctuations are temperature differences?

1. The spatial patterns
on the sky
2. The spectra
3. Physical principles
4. Assumptions based on
general relativity
5. Wikipedia

Back 184

2. The spectra

Front 185

Different curves of space

Back 185

Spherical- parallel lines converge, blobs > 1 degree
Flat- parallel lines remain parallel, blobs = 1 degree
Hyperbolic- parallel lines diverge, blobs < 1 degree

Front 186

What is the furthest distance a
signal could have traveled in the
universe at the time when the CMB
photons were produced?

1. Infinite
2. 14 BLY
3. 380,000 LY
4. 0 LY
5. It depends on how the space
in the universe is curved
6. It depends on speed of CMB
photons

Back 186

3. 380,000 LY

Front 187

What is Dark Energy?

1. the energy associated with dark matter EDARK =MDARK c2
2. The mass-energy needed to balance the effect that gravity has on the expansion of the universe
3. the mass-energy needed to bridge the gap between the mass we know exists and what is needed to make the universe flat
4. The mass-energy which is causing the expansion to decelerate
5. Putin’s secret plan to replace oil

Back 187

3. the mass-energy needed to bridge the gap between the mass we know exists and what is needed to make the universe flat

Front 188

Stars can make Lithium in nuclear reactions but most stars actually DESTROY lithium. Why?

1. It gets fused into other
elements
2. No energy is released by
the fusion of lithium
3. Lots of energy is released
by the fusion of lithium
4. Lithium reacts chemically to
make molecules
5. Stars hate lithium

Back 188

1. It gets fused into other
elements

Front 189

How are conditions in the early universe different from those in the cores of stars (so that more light elements are formed in the early universe)?

1. different temperatures
2. different densities
3. gravity stronger in cores of stars
4. same conditions but existing for
different lengths of time
5. inflation affects the nuclear
reactions in the early universe
6. different anti-boson shielding
factors

Back 189

4. same conditions but existing for
different lengths of time

Front 190

The Relative number of light
elements tells us...

Back 190

the DENSITY of baryonic (normal)
matter at the time when the
universe was hot enough to fuse
nuclei

WHY?
Higher density -> more collisions ->
more nuclear reactions -> more
“heavy” elements
lower density -> fewer collisions ->
fewer nuclear reactions -> fewer
“heavy” elements

Front 191

Why do opposite sides of the universe have the same temperature, even though they seem too far apart for light (and heat) to have traveled from one side to the other in the age of the universe?

1. heat could travel much faster in the early universe, allowing them to exchange heat while the universe was young
2. they were originally close together but then a superfast expansion carried them far apart
3. because of the curvature of space, very distant regions are actually the same point
4. the big bang started in one place so everything was initially at the same temperature

Back 191

2. they were originally close together but then a superfast expansion carried them far apart

Front 192

Diameter of milky way

Back 192

100,000 Ly

Front 193

Sun's distance to the center of galaxy

Back 193

25,000 Ly

Front 194

distance to nearest galaxy

Back 194

2 million light years

Front 195

distance to nearest star

Back 195

4 Ly

Front 196

Time dilation formula

Back 196

t = (t_o)/squr(1-(v/c)^2))

Front 197

Length dilation formula

Back 197

L = L_o * squr(1-(v/c)^2)

Front 198

Circumference of a circle

Back 198

2piR

Front 199

Volume of sphere

Back 199

4/3 pi r^3

Front 200

area of a circle

Back 200

pi r^2