Final section

Question 1

Galileo and the early days

Answer 1

Galileo saw individual stars in the milky way
–could everything that was seen though telescopes be part of the milky way? - was milky way actually the entire universe?

Question 2

Nebula

Answer 2

Planetary nebula, supernova remnants, dark nebula, emission nebula, reflection nebula

In mid-1880s there was another class of nebula examined

Looked at a set of nebula catalogued by William Herschel
-these were strange objects with a spiral shape - became known as SPIRAL NEBULA

Question 3

Two camps about spiral nebula

Answer 3

Lord rose
-followed Immanuel Kant’s idea of “island universe’ far beyond the Milky way - not very well accepted

Others
-spiral nebula were just another form of nebula in the milky way - more accepted view

caused a major division in astronomy

Question 4

Debate into the 1920s

Answer 4

April 1920 - National academy of science in Washington DC held a meeting to settle the debate

• –known as the Shapley-curtis debate
• –two astronomers invited to debate the subject

Harlow Shapley

• –young astronomer
• –famous for his recent determination of the size of the milky way (100,000 lightyears)
• –thought spiral nebula were small objects scattered around inside the milky way
• -similar to globular clusters that he had studied

Heber Curtis

• –older, experience astronomer
• –believed in the island universe model
• –said the spiral nebula were large rotating systems of stars far away from the milky way

Question 5

Entrance of Edwin Hubble

Answer 5

Hubble was a lawyer by trade

• -left his law practice to follow love of astronomy
• –studied in Chicago then Cali
• –1823 he examined the largest of the spiral nebula, the Andromeda Nebula

From two separate photographs he thought he had found a nova

• upon further examination he found that the object was actually a cepheid variable
• –over next few months he found several cepheids
• –knew of the work of Henrietta Leavitt on Cepheids in the SMC
• –discovery of Cepheids inM31

Question 6

Distance of M31

Answer 6

Hubble used the period-luminosity relation to find the absolute magnitude of the cepheids

• today we know he used the wrong relation - Leavitt had only one relation for all cepheids
• but there are two separate period-luminosity relations
• -however his results were close enough

Current number put M31 at 2.2 million lightyears

• this was far beyond the size of the milky way determined by Shapley
• the debate was ended

Question 7

Spiral nebula to spiral galaxies

Answer 7

Spiral nebula are now known as spiral galaxies

• Of which the milky way is just one
• there are now known to be billions of galaxies in the universe

Question 8

The earth’s place in the milky way

Answer 8

What is earths place in the universe - as usual earth stars at the center of things

• –for a long time the sun was thought to be at the center of the milky way
• –story beings in 1780s with William Herschel (who discovered Uranus)

Question 9

The earth’s place in the milky way

Answer 9

What is earths place in the universe - as usual earth stars at the center of things
—for a long time the sun was thought to be at the center of the milky way

Story beings in 1780s with William Herschel (who discovered Uranus)

• –to find center of Milky way Herschel counted stars in different directions
• –selected 683 regions around the sky
• –he believed that the highest concentration of stars would be toward the center
• –his date was almost completely constant over all 683 regions
• –therefore he concluded that the sun was the center of the milky way

Question 10

Kapteyn’s attempt

Answer 10

Jacobus Kapteyn was dutch astronomer

• –he studied the brightness and proper motion of a large set of stars
• –he concluded that the milky way was 55,000 lightyears in size with the sun at the center
• –we now know BOTH men were WRONG
• the reason why didn’t become clear until 1930s

Question 11

Trumpler’s discovery

Answer 11

1930 Robert Trumpler was studying star clusters

• –he noticed that some clusters appeared fainter than they should have
• –he rightly concluded that space is not a perfect vacuum and is filled was dust and gas which scatters light
• –this scattering called INTERSTELLAR EXTINCTION
• –this extinction meant that Herschel and Kapteyn were only seeing the local stars

Question 12

The globular clusters

Answer 12

in 1910s Harlow Shapley looked out of the plane to see the globular clusters

Question 13

Shapley and the globular clusters

Answer 13

in 1910s Harlow Shapley looked out of the plane to see the globular clusters

• -he found RR Lyrae variables which he felt were just another type of Cepheid
• -he used the absolute magnitude of stars on the horizontal branch to find the distance of 93 globular clusters
• -the clusters were not centered on the earth

Shapley found that the globular clusters were centered around a point in the direction of Sagittarius

• -this he correct concluded was the center of the milky way
• –some of the clusters were around 100,000 lightyears from the sun therefore he concluded this was the size of the milky way
• -now we need to examine the overall shape of the milky way

Question 14

Infrared observations

Answer 14

Used to study the location of interstellar dust

• starlight heats the dust to 10 to 90 K
• a blackbody of this temp emits strongest in the far infrared
• in 1983 the IRAS (infrared astronomical satellite) scanned the sky in the far infrared
• in 1990 the COBE satellite scanned the sky in the near-infrared to see the stars

Question 15

Size of the Milky way (disk, central bulge, halo)

Answer 15

Parts of the milky way:
Disk
—between 100,000 and 160,00 lightyears in diameter
—up to 3000 lightyears thick

central bulge

• -around the nucleus
• –6500 lightyears in diameter

Halo
—the globular clusters trace out the halo population

Question 16

The halo

Answer 16

This is the spherical distribution of older stars

• old, metal-poor, pop II stars
• cooler stars, so Halo is more reddish in color
• -globular clusters contain only 1% of halo stars
• -most of halo is individual stars - orbit in paths tilted at random angles - from our perspective they are moving at high speeds - therefore they are called high-velocity stars - in reality we are the high-velocity star

Question 17

The bulge region

Answer 17

This is a region in the center of the milky way

• contains both Pop I and Pop II stars
• appears reddish bc it contains many red giants and red supergiants
• the bulge is slightly peanut shaped which might suggest that the milky way is a barred spiral

Question 18

The disk

Answer 18

Home of the sun at about 26,000 lightyears from the nucleus

• these are all pop I stars
• this region appears blueish bc of the hot O and B stars that are found in the disk
• since we have O and B stars the disk must be a younger pop of stars
• there must also be current star formation occurring in the disk

Question 19

More than one disk

Answer 19

The thick disk

• –more metal rich stars than halo
• -3000 lightyears thick
• -faster moving stars

the thin disk

• -most metal rich stars
• -1000 lightyears thick

Question 20

A closer look at the disk

Answer 20

We know the disk has current star formation

• this implies clouds of hydrogen gas
• we can’t find this gas in the optical, but we can look to radio astronomy
• we use the 21 cm line to find cold clouds of hydrogen gas
• this 21 cm line is created by a spin flop of the electron in the hydrogen atom
• the slight diff in energy is emitted as 21 cm radiation

Question 21

The spiral of arms

Answer 21

Traces of the 21 cm line show the milky way to be a spiral galaxy

we find four major spiral arms in the milky way

• –the sagittarius arm
• -the centaurus arm
• –the cygnys arm
• -the perseus arm
• ——side arm is called the Orion arm - sun is on a little extension of the orion arm

Question 22

The spiral of arms

Answer 22

Traces of the 21 cm line show the milky way to be a spiral galaxy

we find four major spiral arms in the milky way

• –the sagittarius arm
• -the centaurus arm
• –the cygnys arm
• -the perseus arm
• ——side arm is called the Orion arm - sun is on a little extension of the orion arm

Question 23

Galaxy rotation

Answer 23

In a solid body rotation the outer part rotates with a higher velocity than the inside

• for orbits that obey Kepler’s law the outside star orbit with a slow velocity
• -observations show that stars near the sun all orbit at the same velocity
• —–this means stars inside move around much quicker

Question 24

Galaxy rotation

Answer 24

In a solid body rotation the outer part rotates with a higher velocity than the inside

• for orbits that obey Kepler’s law the outside star orbit with a slow velocity
• -observations show that stars near the sun all orbit at the same velocity
• —–this means stars inside move around much quicker

Question 25

Orbit of the sun

Answer 25

Sun orbits the center of the galaxy in a nearly circular orbit - -26,000 lightyears in radius - and a period of 220 million years - --however, the sun isn't orbiting one object like a planet orbiting the sun - --all the mass inside the sun's orbit effects the suns orbit

Question 26

Kepler's law

Answer 26

We can rearrange the equation to get an estimate of the mass inside the suns orbit 26,000 ly = 2.5 x 10^20 m - --use this and 220 million years for the period - --this gives 1.8 x 10^41 kg - --or.. 9.0 x 10^10 solar masses

Question 27

Mass inside the sun

Answer 27

We just found 9.0 x 10^10 solar masses inside the sun's orbit - --however, there is lot of material outside the suns orbit - if we look at the orbits of stars further out than the sun, we can cont to get mass estimates - eventually the mass should run out and orbital speeds slow down (like the solar system) - however this is not what we see

Question 28

Where is the edge?

Answer 28

We don't seem to find the end of the milky way in terms of mass - however we don't see the luminous material like stars - current estimates for the mass of the milky way could be as much as 6.0 x 10^11 solar mass or more

Question 29

The missing mass

Answer 29

Since the velocities don't drop off there must be a lot of mass to the outside of the sun - --however, we can't see the mass, its not int he form of stars - --therefore the matter is dark of DARK MATTER there are lots of theories - -blackholes - -MACHOS (massive compact halo objects) - -WIMPs (weakly interacting particles) - -dark energy

Question 30

The heart of the milky way

Answer 30

Center of the milky way ---this is in the direction of the constellation of Sagittarius Black hole lurking at the center - -we now think that there is a massive black hole at the center of the milky way - -3.7 x 10^6 solar mass black hole by current estimates of objects orbiting near the center - this is not as active as galaxies we will see in later lessons

Question 31

How was Shapley-curtis debate settled?

Answer 31

Edwin Hubble found the distance to M31 and it was far outside the size of the milky way as determined by Shapley

Question 32

The time is takes the sun to orbit the center of the milky way

Answer 32

220 million years

Question 33

The thickness of the thin disk

Answer 33

1000 lightyears

Question 34

the diameter of the milky way

Answer 34

100,000 to 160,000 lightyears

Question 35

the mass inside the suns orbit

Answer 35

9.0 x 10^10 solar masses

Question 36

the distance from the sun to the center of the milky way

Answer 36

26,000 lightyears

Question 37

the thickness of the thick disk

Answer 37

3000 lightyears

Question 38

the estimated total mass of the milky way

Answer 38

6.0 x 10^11 solar masses

Question 39

the mass of the central black hole of the milky way

Answer 39

3.7 x 10^6 solar masses

Question 40

the distance to M31, the nearest large galaxy

Answer 40

2.2 million lightyears

Question 41

What objects are used to determine the distance of M31

Answer 41

Cepheid variable

Question 42

What do we believe to be in the middle of the milky way galaxy

Answer 42

a massive black hole

Question 43

How many arms does the milky way have

Answer 43

4

Question 44

T/F - The results of herschel and Kapteyn were both biased due the the existence of interstellar extinction

Answer 44

TRUE

Question 45

What do we use to map the shape of the spiral arms of the milky way?

Answer 45

21 cm radiation from neutral hydrogen

Question 46

What do we use to map the shape of the spiral arms of the milky way?

Answer 46

21 cm radiation from neutral hydrogen

Question 47

Diff types of galaxies

Answer 47

Galaxies come in variety of shapes and sizes -edwin hubble classified galaxies into 4 broad categories called Morphological types system referred to as: -the hubble classification scheme -or Hubble Fork

Question 48

Elliptical Galaxies - E

Answer 48

Named for their elliptical shapes - --have no spiral arms or other distinct features - --hubble classified these galaxies based on how round they were - if they appeared sperical they are EO and if they are cigar shaped they are E7 - however this classification doesn't necessarily mean that this is the true shape of the galaxy - -projection effects - an E7 seen end on might look like an EO - -therefore the Hubble Type for elliptical galaxies is completely based on how they appear in the sky - -about 20% of the observed galaxies

Question 49

Structure of elliptical galaxies

Answer 49

Elliptical galaxies have little or no interstellar gas and dust - -therefore star formation has essentially stopped - we see very few young stars in elliptical galaxies - -they are composed mostly of old, red pop II stars - -therefore elliptical galaxies generally appear redder than spiral galaxies Spiral galaxies are more similar in size - however elliptical galaxies cover a large range of sizes - -they range from - Giant elliptical galaxies with 10^13 solar masses to dwarf elliptical galaxies with 10^5 solar masses - some ppl even consider globular clusters to be very small elliptical galaxies

Question 50

Giant elliptical galaxies

Answer 50

These are the largest galaxies - -200 kpc in diameter (double the milky way) - -up to 100x more massive than the milky way - -they are normally found int he centers of clusters of galaxies - -current theory is that these galaxies have grown bc of cannibalism of smaller galaxies

Question 51

Giant elliptical galaxies

Answer 51

These are the largest galaxies - -200 kpc in diameter (double the milky way) - -up to 100x more massive than the milky way - -they are normally found int he centers of clusters of galaxies - -current theory is that these galaxies have grown bc of cannibalism of smaller galaxies

Question 52

Dwarf elliptical galaxies

Answer 52

Not much larger than a globular cluster - -some as small as 1 kpc in diameter - -smallest contain only about 10^5 solar masses

Question 53

Dwarf elliptical galaxies

Answer 53

Not much larger than a globular cluster - -some as small as 1 kpc in diameter - -smallest contain only about 10^5 solar masses - -most numerous in the universe but very hard to see - --we only really see the local dwarf ellipticals - -they have so few stars you can sometimes look through them without seeing them

Question 54

What happens if we flatten a elliptical to a disk

Answer 54

These are no longer classified as an elliptical galaxy --these are known as lenticular galaxies bc they are lens shaped -in most regards they are more similar to spiral galaxies than elliptical -they are size of spiral galaxies - however they don't show arms (S0)

Question 55

Spiral galaxies

Answer 55

these were the spiral nebula - they are galaxies like the milky way - they make up 77% of the galaxies we currently observe - like they milky way they have: a disk, a halo, and a bulge Their stellar populations are similar to those found in the milky way - -the arms are hot young stars of pop I - they help light up and define the spiral arms of the galaxy - they have the halo of older red stars - in general spiral galaxies tend to be bluer than elliptical galaxies - spirals were classified by hubble with an S - but there are a lot of variety within the spiral galaxies - most of this diff is based on - the size of the bulge and the tightness of the arms - --we classify spirals as sa, sb, or sc

Question 56

Spiral galaxies

Answer 56

these were the spiral nebula - they are galaxies like the milky way - they make up 77% of the galaxies we currently observe - like they milky way they have: a disk, a halo, and a bulge Their stellar populations are similar to those found in the milky way - -the arms are hot young stars of pop I - they help light up and define the spiral arms of the galaxy - they have the halo of older red stars - in general spiral galaxies tend to be bluer than elliptical galaxies - spirals were classified by hubble with an S - but there are a lot of variety within the spiral galaxies - most of this diff is based on - the size of the bulge and the tightness of the arms - --we classify spirals as sa, sb, or sc

Question 57

Sa galaxies

Answer 57

These are spiral galaxies with: - a large bulge - tightly wound arms

Question 58

Sb galaxies

Answer 58

Spiral galaxies with - moderate bulge - looser arms

Question 59

Sc galaxies

Answer 59

Spiral galaxies with - small bugle - very loose arms

Question 60

What are the arms?

Answer 60

The arms cannot be made of anything material since that would wind-up - in the 1940s Bertil Lindblad proposed that the arms might be like ripples in water - as the wave crests, the water bunches up, but then dissipates as the crest passes - you see this when driving on the highway and there is an accident - the cars slow down and then spread out again on the other side

Question 61

Density waves in the galaxies

Answer 61

If we have a density wave in a galaxy it will cause the material to compress - this can trigger for star formation - the hot stars which are formed heat up the surrounding gas and make it glow - this is what we see as the spiral arms - the wave continues to the next region while the O and B stars burn out

Question 62

Problems with the density-wave model

Answer 62

(involves fast motion of interstellar gas and dust - this material is compressed within the spiral arm) - --the first problem is how to keep the density wave going - --the wave should run out of energy - -a second problem deals with the fact that density waves should produce tight, well defined arms - -not all spirals show tight arms

Question 63

Grand design vs. Flocculent

Answer 63

Galaxies which show tight arms are called GRAND DESIGN SPIRALS - other fluffy armed spirals are called FLOCCULENT SPIRALS - -some people explain flocculent spirals with self-propagating star formation instead of density waves - -we have mentioned the idea of one generation of stars starting the next generation - -likely spiral arms are caused by a combination of these two effects

Question 64

Final class of galaxies - irregular galaxies

Answer 64

They are irregular bc they have no fixed shape - -they are commonly caused by the collision of two galaxies or by tidal forces from a large galaxy - -two famous ones are the SMC and LMC

Question 65

Edwin Hubble and Vesto Slipher

Answer 65

In

Question 66

Edwin Hubble and Vesto Slipher

Answer 66

In the 1920s Edwin Hubble was working on the distance to nearby galaxies (100 degrees Mount Wilson) - -he was using the cepheids to get distances to a larger sample - -slipher (1910s, Lowell observatory) - -taking spectra of nearby galaxies - -he was finding shifts in spectral lines (mostly to redshift side)

Question 67

Hubble expansion

Answer 67

Hubble and Humason used the larger telescope at mount Wilson to get redshifts for a larger and fainter sample of galaxies (all redshifts at this point) - -these are the same ones for which they and the distance from the cepheids - like good astronomers they plotted the distance vs. the redshift and found a linear relation - --this is the famous Hubble law - the more distant the galaxy the larger the redshift

Question 68

Hubble Law

Answer 68

Basically the law says that the further away an object is the faster it is moving away --this universal recessional motion is known as the HUBBLE FLOW ``` it can be written as: v = Ho d v - recessional velocity Ho - Hubble constant d - distance ``` the problem is the value of Ho

Question 69

Measurement of Ho in Hubble law

Answer 69

Hubble didn't know about the two separate Cepheid relations or the local motion - -his original number of Ho was a little off - -the value of the Hubble constant was hotly debated for years But we are settling onto a value near 72 km/sec/Mpc (but they could be changing a little) --it is a critical problem which effects our understanding of Cosmology

Question 70

Problems with the hubble law

Answer 70

If the galaxy has a motion other than its hubble flow motion the velocity measured is effected - -this is most easily seen in clusters of galaxies - -the galaxies orbit within the cluster, therefore each cluster member will have a unique redshift - -therefore the hubble law doesn't give the correct distance - -this leads into a discussion of clusters of galaxies

Question 71

Problems with the hubble law

Answer 71

If the galaxy has a motion other than its hubble flow motion the velocity measured is effected - -this is most easily seen in clusters of galaxies - -the galaxies orbit within the cluster, therefore each cluster member will have a unique redshift - -therefore the hubble law doesn't give the correct distance - -this leads into a discussion of clusters of galaxies Would you expect any structure larger than a galaxy?

Question 72

The milky way's group

Answer 72

The milky way is part of cluster known as the local group - this group has about 50 total members - it includes: - --the milky way - --the andromeda galaxy (M31) - --M32 and M33 - --SMC and LMC - --many dwarf elliptical galaxies - --two new members discovered in 1993 and 1997

Question 73

Large rich clusters

Answer 73

The nearest rich cluster is the virgo cluster - -contains about 2000 visible members - -may contain 10,000 members - -50 million lightyears away - -9 million lightyears in diameter - -dominated by 3 giant elliptical galaxies other nearby rich clusters - -the coma cluster - -the hercules cluster - -the centaurus cluster

Question 74

Is there anything larger than a cluster?

Answer 74

We must look at a large sample of galaxies to answer this question - --from their redshifts and directions we can plot a map of the galaxies - -what we find are clusters of clusters - --these are called SUPERCLUSTERS - dozens of clusters - 100s of millions of lightyears across - we also find VOIDS

Question 75

Is there anything larger than a cluster?

Answer 75

We must look at a large sample of galaxies to answer this question - --from their redshifts and directions we can plot a map of the galaxies - -what we find are clusters of clusters - --these are called SUPERCLUSTERS - dozens of clusters - 100s of millions of lightyears across - we also find VOIDS

Question 76

Voids

Answer 76

Voids are regions of few if any galaxies - -there is a lot of debate just how empty these voids really are - -this is Dr. Moody's research here at BYU - -the existence of voids and superclusters are important tools in our understanding of the origins of the universe

Question 77

Other features seen in maps of galaxies

Answer 77

Due to internal motion within clusters, we see lines in the plots which point back to the earth - these are sometimes called the fingers of God The great wall - --250 x 750 million lightyears - --voids on either side the southern wall ---similar but smaller than the great wall

Question 78

Missing mass again

Answer 78

Clusters of galaxies must be held together by gravity - --however, the visible mass we see in clusters isn't enough - -therefore we have another missing mass problem - -about 10% of this problem in clusters can be explained by intracluster gas, the remainder is dark matter

Question 79

Missing mass again

Answer 79

Clusters of galaxies must be held together by gravity - --however, the visible mass we see in clusters isn't enough - -therefore we have another missing mass problem - -about 10% of this problem in clusters can be explained by intracluster gas, the remainder is dark matter

Question 80

What are the largest galaxies we see?

Answer 80

Giant elliptical galaxies

Question 81

How do we think giant elliptical galaxies got so large?

Answer 81

By galaxy cannibalism - they ate smaller galaxies

Question 82

What are most commonly observed galaxies in the universe

Answer 82

Spiral galaxies

Question 83

Which type of galaxies are most common?

Answer 83

dwarf galaxies

Question 84

T/F we think the majority of irregular galaxies come from collisions

Answer 84

TRUE

Question 85

T/F All galaxies start out as EO galaxies and proceed along the Hubble Fork over time

Answer 85

FALSE

Question 86

T/F galaxies with tight, narrow arms are formed by self-propagating star formation

Answer 86

FALSE -self propagating star formation tends to move in random directions and therefore wouldn't produce tight, well defined spiral arms

Question 87

Discuss the meaning of Hubble Law

Answer 87

The Hubble Law states that the more distant the galaxy the larger the redshift. This law explains that the further away the celestial object is, the faster it is moving away. It uses the Hubble Constant multiplied by the distance to find the recessional velocity. However, Hubble law is incorrect when it comes to clusters of galaxies because its motion differs where each member in the cluster has a different redshift.

Question 88

Disucc the structures larger than a galaxy that we find in the universe

Answer 88

One group larger than a galaxy is the Local Group, which contains the Milky Way, Andromeda Galaxy, M32, M33, SMC, LMC, and many dwarf elliptical galaxies. Another rich cluster is the Virgo Cluster, which is dominated by three giant elliptical galaxies, as well as the Coma Cluster, Hercules Cluster, and Centaurus Cluster. There are also voids and superclusters in the Universe.

Question 89

Disucc the structures larger than a galaxy that we find in the universe

Answer 89

One group larger than a galaxy is the Local Group, which contains the Milky Way, Andromeda Galaxy, M32, M33, SMC, LMC, and many dwarf elliptical galaxies. Another rich cluster is the Virgo Cluster, which is dominated by three giant elliptical galaxies, as well as the Coma Cluster, Hercules Cluster, and Centaurus Cluster. There are also voids and superclusters in the Universe

Question 90

Theory of relativity

Answer 90

According to Newton (or classic physics) the universe is uniform and filled with a rigid frame work --time passes as a constant at all times In 1905 Albert Einstein revolutionized physics and astronomy with his Special Theory of relativity --the first principle is: the fundamental laws of the universe do not depend on a person's location or motion

Question 91

Special theory of relativity

Answer 91

This is the first of two theories - in 1865 James Maxwell had described the basics of electromagnetism - the theories predicted effects based on the motion of electric charge - this implies an absolute frame of reference Einstein didn't like absolute reference frames - Einstein's goal was to eliminate the assumption of absolute space - -this primary conclusion was that everyone measured the same speed of light regardless of their motion - -this goes against Newtonian theory The second principle is: the speed of light is the same for all observers

Question 92

Two principles of special theory of relativity

Answer 92

First: the fundamental laws of the universe do not depend on a person's location or motion second: the speed of light is the same for all observers

Question 93

Newtonian motion

Answer 93

As seen by outfielder, ball is approaching her at (40 m/s + 10 m/s) = 40 m/s Because batter hits ball at 30 m/s --> and running outfielder catches ball at 10 m/s

Question 94

Motion of light

Answer 94

Astronaut with flashlight: light 3x10^8 m/s ---> Astronaut flying in spaceship 1 x 10^0 m/s

Question 95

New way of thinking

Answer 95

The laws of physics can't be changed by your individual motions - this leads to space-time no longer being a fixed rigid object - motion effects there ate at which clocks keep time, the length of objects which we measure, the mass of obejects

Question 96

Lorentz transformations

Answer 96

Dutch Physicist Hendrik Lorentz formalized Einstein's theory into equations These equations show at high velocity: - -time slows down - -lengths get shorter - -mass increases is this all just theory?

Question 97

Tests of special relativity

Answer 97

To test the theory two identical atomic clocks were used - -one was flown on a high speed aircraft - -the second stayed on ground - -when the plane returned the clocks showed diff times - -in particle physics many of the other predictions are seen

Question 98

Other principles (relativity)

Answer 98

- -the speed of light is constant in a vacuum - -nothing can go faster than the speed of light - -no massive object can move at the speed of light - -the special theory of relativity only applies to non-acceleration reference frames, in other words, at constant velocities - -if we allow for accelerations we move on to the GENERAL theory of relativity

Question 99

General theory of relativity

Answer 99

Published in 1915 by Einstein

Question 100

General theory of relativity

Answer 100

Published in 1915 by Einstein - -involves the effects of gravity - Einstein argued that gravity causes accelerations - therefore it must affect the shape of space-time itself - --this allowed Einstein to think of gravity as a motion rather than a force - -this is the PRINCIPLE OF EQUIVALENCE

Question 101

Curved space-time

Answer 101

This (After principle of equivalence) led Einstein to the idea that gravity also effects clock, lengths, etc. - -therefore he had a more general theory - -in this view gravity can be viewed as a bending or warping of space itself - -far from any massive object space is flat - -near massive objects it is bent into a 'well' If i role a ball across flat space it moves in a straight-line --if i role it on curved space its direction is changed 1. massive object curves the space-time around us 2. far from the object, space-time is nearly "flat", close to the object, the curvature forms a "Well" 3. in Einsten's picture of gravity other objects sense the curvature and are drawn into the "well"

Question 102

What can we predict from general relativity?

Answer 102

The motion of the planets | the blending of light

Question 103

The precession of mercury

Answer 103

In mid-1800s Le Verrier noted that Newtonian mechanics didn't predict the position of mercury very well - -Einstein found that where gravity was weak relativity and newtonian mechanics matched - -however, in a strong gravitational field general relativity predicted a diff orbit - -general relativity predicted the correct orbit

Question 104

The bending of light

Answer 104

Newtonian mechanics would say that light wouldn't be bent bc it has no mass - -general relativity predicts bending - -to test this the positions of stars were examined during a solar eclipse in 1919 - -stars which should have been behind the sun were visible at the edge of the sun - -this effect is also seen in clusters of galaxies and with quasars

Question 105

The bending of light

Answer 105

Newtonian mechanics would say that light wouldn't be bent bc it has no mass - -general relativity predicts bending - -to test this the positions of stars were examined during a solar eclipse in 1919 - -stars which should have been behind the sun were visible at the edge of the sun - -this effect is also seen in clusters of galaxies and with quasars

Question 106

Escape of light

Answer 106

If gravity effects light then what of light leaving a massive object - -the effect of the gravity would be to shift the light to a longer wavelength - this was seen in 1960 by Pound and Rebka - -the effect called GRAVITATIONAL REDSHIFT - the effect has since been seen from light escaping the surface of a white dwarf

Question 107

Gravitational redshift

Answer 107

A. the gravitational slowing of time ---compared to a clock on the top floor, a clock on the ground floor is deeper in the earth's gravitational field and so ticks more slowly B. gravitational redshift ---as light wave climbs in a gravitational field, its frequency decreases and its wavelength increases

Question 108

Gravitational waves

Answer 108

The fourth prediction of general relativity is gravitational waves - -these occur when objects move, like a ship moving through water - -this creates a wake that propagates through space - -these waves are called gravitational waves or gravitational radiation There has not been a direct measure of gravitational waves - -however, Russell Hulse and Joseph Taylor found indirect evidence from a binary pair of neutron stars - -the pulses from one of the stars were monitored as the stars orbited - -evidence is that gravitational waves exist - -they won the Nobel Prize in 1993

Question 109

Relativity

Answer 109

General relativity has never made a wrong prediction - -newtonian mechanics only applies at low speeds and weak gravity - -the results of general relativity lead us into some very interesting subjects: black holes, warped space, and wormholes

Question 110

Relativity

Answer 110

General relativity has never made a wrong prediction - -newtonian mechanics only applies at low speeds and weak gravity - -the results of general relativity lead us into some very interesting subjects: black holes, warped space, and wormholes

Question 111

Effects of general relativity

Answer 111

Remember that mass warps space-time - -this warping can even cause light to bend - -what would happen if the warp was so big that not even light could climb out of the "well" - -this lead us to the topic of black holes - -story begins with neutron stars

Question 112

Neutron stars

Answer 112

Remember that neutron stars were held up by neutron degeneracy - -like electron degeneracy this could sonly hold up so much mass - -what happens if a core is larger than this limit? - -we now enter a world of pure theory

Question 113

Black hole

Answer 113

The core would continue to collapse down to a point - -as it shrinks its surface gravity increases - -with the increasing surface gravity the escape velocity increases - -eventually the core will collapse inside a sphere at which point the escape velocity becomes greater than the speed of light - -this object is now a black hole

Question 114

Curvature of space

Answer 114

1. Black hole sharply curves the space-time around it 2. far from the black hole space-time is nearly "flat" close to the black hole, the curvature forms a "well" that is infinitely deep 3. objects that venture too close to the black hole cannot escape from the "well"

Question 115

The event horizon

Answer 115

Once object shrinks within the surface to where escape velocity = speed of light it disappears from normal space - --the point where escape velocity just equals the speed of light is called the EVENT HORIZON - --this is sometimes called the surface of the black hole - --once inside the event horizon material is permanently lost to the universe

Question 116

The singularity

Answer 116

Once the matter is inside the event horizon nothing can stop its collapse - -the entire mass of the core will be compressed into a single point with no dimensions - -the black hole now has two parts - the singularity down to the center and the event horizon fro a surface

Question 117

Linearity of time

Answer 117

We living in a world where we can move in space, but are confined to linear time - -in a black hole the laws of the physical universe are changed - -the gravity inside a black hole distorts space and time so strongly that space and time become interchanged - -you are free to move in time, but are confined to the singularity of a point in space - -chaos reigns inside the black hole

Question 118

Cosmic censorship

Answer 118

We are protected from chaos of the singularity by the event horizon --if we remain outside the event horizon we are sage The fear of singularities was so strong that in 1969 Penrose and colleagues gave us LAW OF COSMIC CENSORSHIP - -no such thing as a naked singularity - -entering or leaving a black hole must be done across the event horizon

Question 119

Cosmic censorship

Answer 119

We are protected from chaos of the singularity by the event horizon --if we remain outside the event horizon we are sage The fear of singularities was so strong that in 1969 Penrose and colleagues gave us LAW OF COSMIC CENSORSHIP - -no such thing as a naked singularity - -entering or leaving a black hole must be done across the event horizon

Question 120

Science fiction and black holes

Answer 120

Some poor science fiction describe black holes as giant vacuum cleaners sucking up everything around them ---VERY INACCURATE The effects of a black hole only occur very near to the singularity - -for a 10 solar mass object the effects are within 1000 km - -beyond this point things are norma - --if the sun became a black hole the planets would continue in their obrits

Question 121

Crossing the event horizon

Answer 121

If you watched a ship approach the event horizon from the outside you would see - --the ship take an infinite amount of time to cross the event horizon - -the ship would progressively get redder If you were on the ship: - -your time would run normal - -you would fall into the singularity - -this would not be a fun experience - -the differential gravity would pull you apart

Question 122

Two types of black holes

Answer 122

We can describe every black hole by 3 numbers - -the mass - -the electric charge (not expected to have much electric charge) - -the angular momentum or spin From this we find two types of black holes - --Schwarzschild black hole (non rotation) - -Kerr black hole (rotating)

Question 123

Schwarzchild black hold

Answer 123

Non-rotating black holes --these are objects we have been discussing --Karl Schwarzschild came up with a simple equation to describe the size of the event horizon Rsch = (2GM)/c^2 ---Rsch = Schwarzschild radius --for a 10 solar mass star the radius is 30 km

Question 124

Kerr black hole

Answer 124

Rotating black holes - -much more likely since almost all stars rotate - -bc of the rotation these objects effect a slightly larger region of space-time - -the rotating black hole drags the space near the event horizon around with its rotation - -you are not inside the event horizon, but you are effected - -this region is called the ERGOSPHERE

Question 125

Kerr black hole

Answer 125

Rotating black holes - -much more likely since almost all stars rotate - -bc of the rotation these objects effect a slightly larger region of space-time - -the rotating black hole drags the space near the event horizon around with its rotation - -you are not inside the event horizon, but you are effected - -this region is called the ERGOSPHERE

Question 126

Evidence of black holes

Answer 126

Since by definition we can't see a black hole how do we know if any exist? - -we have been speaking completely theoretical up to this point - -the way we detect a black hole is by its effect on another object - -the most likely objects to be black holes are strong X-ray sources - Cygnus X-1, Hercules X-1

Question 127

Cygnus X-1

Answer 127

The X-rays flickered on time scales of hundredths of a second - -this said the object was very small - -however, the X-ray emission was traced to the star HD 226868 - -the star could not be the source of the pulses - -from spectroscopy the system was found to be a binary with the second object being a black hole

Question 128

related ideas to general relativity

Answer 128

General relativity allows some very strange geometers - -in the 1930s Einstein and Nathan Rosen discovered a mathematical construct that would connect our space time with a separate space time - -in other words a bridge to an ALTERNATE UNIVERSE - -this is called an Einstein-rosen bridge - -what if the bridge didn't connect different universe, but two points in the same universe?

Question 129

The wormhole

Answer 129

A bridge btwn two points in the same universe is called a wormhole - -but remember that it is space-time not just space - -unfortunately a wormhole will disappear almost as fast as it formed - -there are some modern theories to keep a wormhole open A wormhole connects our universe to itself - like a "U"

Question 130

The wormhole

Answer 130

A bridge btwn two points in the same universe is called a wormhole - -but remember that it is space-time not just space - -unfortunately a wormhole will disappear almost as fast as it formed - -there are some modern theories to keep a wormhole open A wormhole connects our universe to itself - like a "U"

Question 131

What applies to the Special theory of Relativity

Answer 131

- -time runs slower - -lengths get shorter in the direction of motion - -mass increases at higher velocity

Question 132

Of the four major predictions of general relativity, for which one do we not have a direct measurement?

Answer 132

gravitational waves

Question 133

Let's say I shot a laser beam straight up a tall building. The wavelength of light that leaves my laser is 450 nm. Which of the following values might we measure at the top of the building for the wavelength of the laser light. (assume general relativity is correct) (This might take some thought)

Answer 133

460 nm

Question 134

T/F passing through a wormhole it is possible to go back in time?

Answer 134

TRUE - it connects two points in spacetime

Question 135

What do we call the surface where the escape velocity equals the speed of light?

Answer 135

The event horizon

Question 136

If the sun were to instantly become a black hole, what would happen to solar system?

Answer 136

The planets, and everything else, would maintain their current orbits

Question 137

T/F we have mentioned the problem of dark matter before. The bending of light can show us the presence of dark matter?

Answer 137

TRUE

Question 138

If i have two black h oles and the first has twice the mass of the second, which is true?

Answer 138

The radius of the event horizon for the first is twice as big as the second

Question 139

What is an effect of gravitational lensing

Answer 139

- -the position of a distant object being shifted. In some cases being able to see an object that should be behind another object - -multiple images of the same object - -arcs of light from distant objects - -seeing a brightening due to a focusing effect like a magnifying glass

Question 140

T/F according to general relativity it is impossible for there to be alternative universes

Answer 140

FALSE

Question 141

T/F you are inside a box that you cannot see outside of. You hold up a ball four feet above the bottom of the box. You let it go and it galls to the bottom of the box. From this you know that a gravitational force has pulled the ball down

Answer 141

FALSE - it is also possible that an acceleration has happened

Question 142

Describe motion on a curved surface - use proper terminoloy

Answer 142

If you roll a ball on a straight surface, the ball moves in a straight line. However, on a curved surface, the ball will follow the curve as it rolls and therefore change its original path of motion.

Question 143

Early galaxies

Answer 143

The formation of galaxies is still a bit of a mystery --related question is why spiral vs. elliptical there are three current theories for the formation of galaxies - -a single huge primodial gas cloud forms a single galaxy - -several moderate size clouds merge to from a galaxy - -a lot of little clouds coalesce to form a galaxy

Question 144

Clues to the mystery of galaxy formation

Answer 144

- -In clusters of galaxies spirals are to the outside and elliptical to the inside - -at high redshifts there are more spiral galaxies than in the local region - -however, collisions of large spirals don't produce elliptical or SO galaxies The HST has found some unique galaxies at high redshift --11 billion ly away ---small irregular shaped objects --many close together --theory is that these clouds have combined to form larger galaxies HST also found chain galaxies which might be these small galaxies merging

Question 145

Rate of star formation

Answer 145

The secret to galaxy formation might be the rate at which stars form Current theory - -in elliptical galaxies there is a rapid star formation, which then shuts down - -in spirals the stars form gradually over time. This gives time to form the disk - -both of these could then be affected by our next subject

Question 146

Rate of star formation

Answer 146

The secret to galaxy formation might be the rate at which stars form Current theory - -in elliptical galaxies there is a rapid star formation, which then shuts down - -in spirals the stars form gradually over time. This gives time to form the disk - -both of these could then be affected by our next subject

Question 147

Strange objects - (Quasars - early galaxies?)

Answer 147

Story begins in 1936 with Grote Reber - -he built first radio telescope in his backyard in Illinois - by 1944 he had found 3 very strong radio sources in the sky (beginning of radio astronomy) - -these objects are labeled with a constellation name and a latter (Sagittarius A, Cassiopeia A, Cygnus A) What were these objects? - -Further investigation found Sag A and Cas A were within the milky way - Sag A was center of milky way and Cas A was a supernova remnant - -however this left Cyg A to study - Walter Baade and Rudolph Minkowski used the Palimar 200 telescope to examine region around radio source - found a strange looking galaxy

Question 148

Strange objects - (Quasars - early galaxies?)

Answer 148

Story begins in 1936 with Grote Reber - -he built first radio telescope in his backyard in Illinois - by 1944 he had found 3 very strong radio sources in the sky (beginning of radio astronomy) - -these objects are labeled with a constellation name and a latter (Sagittarius A, Cassiopeia A, Cygnus A) What were these objects? - -Further investigation found Sag A and Cas A were within the milky way - Sag A was center of milky way and Cas A was a supernova remnant - -however this left Cyg A to study - Walter Baade and Rudolph Minkowski used the Palimar 200 telescope to examine region around radio source - found a strange looking galaxy

Question 149

Spectrum of Cyg A

Answer 149

Baade and Minkowski took a spectra of Cyg A - -instead of normal absorption lines from a normal galaxy they saw emission lines - -the lines were shifted 5.7% to the red or a recessional velocity go 17,000 km/sec - -using Hubble's law puts this object at about 750 million ly Cyg A was at a huge distance but was still extremely bright to an amateur radio telescope on the earth - -turns out Cyg A puts out 10,000,000 times more radio energy than M31 (normal local galaxy) - -what could be putting out that much more energy from an apparently normal galaxy?

Question 150

3C catalogue

Answer 150

After the original three radio sources, work began to find more objects - 1858 the 3C catalogue was published - contained 471 strong radio sources - 1960 Allen sand age looked at 3C 48 - instead of dinging a strange galaxy at the coordinated he found a "star" Star? - -stars don't putout strong radio signals so 3C 48 could not be a star - -spectrum was once again taken - this again showed emission lines - couldn't identify lines this time - -some thought it was just a strange star in our own galaxy - -then in 1962 astronomers looked at 3C 273 and found another "star" with emission lines

Question 151

Mystery to 3C 48 and 273

Answer 151

Solution required a jump in logic - -astronomers were so familiar with nearby objects they couldn't identify the lines - -1962 Schmidt at Caltech looked at the spectrum of 3C 273 and realized the emission lines were known lines, in particular hydrogen lines - -lines were at enormous redshifts (about 15% the speed of light - implies 2 billion ly of distance)

Question 152

Quasars

Answer 152

A star at 2 billion ly could never be seen - new objects -to make matters worse 3C 48 was found to be receding at 37% speed of light or distance of 4 billion ly these objects had 2 main characteristics - -strong radio sources - -looked like stars - -these two characteristics combine into the name Quasi-stellar radio sources - Quasar-stellar objects (QSOs) - --we now know only about 10% of quasars are 'radio-loud' - -however name stuck - -more than 10,000 quasars known to exist

Question 153

Quasar redshifts

Answer 153

redshifts range from .06 to 7.00 - -must have redshifts of .3 or more - -their recessional velocities are high enough to be relativistic - -some 94% speed of light or 10 billion ly from earth - -most distant are 13.5 billion ly - -light left before the sun was formed there are no close by quasars - closest is 800 million ly away - -when we talk about distance we are talking about how they looked many years in the past - -therefore quasars are object from an earlier era in the history of the universe - give us clues to the early universe

Question 154

Clues to the nature of quasars

Answer 154

Quasar have turned out to be associated with remote galaxies ---radio-quiet quasars in spirals --radio loud quasars in ellipticals Spectra of quasars are unique in the fact that they show non-blackody emission - -they have source of energy other than the light produced by temp (thermal radiation) - -show non thermal radiation which is often polarized - -this can come from synchrotron radiation - -production of synchrotron radiation could be evidence for an accretion disk around a black hole

Question 155

Clues to the nature of quasars

Answer 155

Quasar have turned out to be associated with remote galaxies ---radio-quiet quasars in spirals --radio loud quasars in ellipticals Spectra of quasars are unique in the fact that they show non-blackody emission - -they have source of energy other than the light produced by temp (thermal radiation) - -show non thermal radiation which is often polarized - -this can come from synchrotron radiation - -production of synchrotron radiation could be evidence for an accretion disk around a black hole

Question 156

Closer quasars?

Answer 156

Remember there are no close by quasars --are there any objects similar to quasars which are closers? YES - seyfert galaxies, radio galaxies, blazars, and BL Lacs

Question 157

Seyfert galaxies

Answer 157

1943 Carl Seyfert began working on spiral galaxies with very compact nuclei - -nuclei were brighter than those found in other galaxies - this was evidence of violent activity - -had strong emission lines like quasars - -other characteristics - radio emission (quiet) and cray emission - -now called SEYFERT GALAXIES About 10% of brightest spirals are seyferts - -700 currently known - range in brightness from faintest quasars down to normal galaxies - -really do provide bridge - -research on objects at BYU with ROVER telescope

Question 158

Radio galaxies

Answer 158

similar way to radio-loud and radio-quiet quasars the seyferts have a counterpart - -we find active elliptical galaxies which we call Radio galaxies - -the first of these galaxies discovered in 1918 by Heber Curtis - -took short image of M87 - -found bright nucleus and jet of material 1960s astronomers examined extragalactic radio sources - -found most radio galaxies had 2 RADIO LOBES with a giant elliptical galaxy at center - -lobes were 5 to 10 times the size of the parent galaxy - -bc of the shape these are sometimes called DOUBLE RADIO SOURCES

Question 159

Head-tail radio sources

Answer 159

Some radio galaxies with a 'head' of strong radio remission and a 'tail' of weaker emission trailing behind - -these are head-tail radio sources - -just like smoke from a moving train ejected material in these objects lags behind as the galaxy moves through the intergalactic medium

Question 160

Blazars

Answer 160

Similar to quasars with extraordinary variability - -the first of these new objects was BL lacerate - discovered in 1929 and mistaken for variable star - -Bl Lac had no features in its spectrum - -images showed a faint fuzz around BL lax which turned out to be an elliptical galaxy - BL Lax was first of a group of galaxies called BLAZARS - -show jets which appear to move faster than light - -also show variations which can be as large as 5 magnitudes - they are radio sources - -probably double lobe sources seen end on so we are looking down the jet

Question 161

Engines of blazars

Answer 161

What kind of object drive all these amazing galaxies - variability of blazers give us a clue - --period of variation is related to size of the changing object - -if the period is 1 year then the size of the object can't be larger than 1 ly - -this is called a LIGHT TIME ARGUMENT - -from this argument the engines of active galaxies are about the size of our solar system

Question 162

Light time arguments

Answer 162

1. an object 1 light year across emits a sudden flash of light 2. first light that we receive comes from A (the part of the object nearest to earth) 3. light from B (center of object) has to travel an additional 1/2 ly to reach earth, so we see this light 1/2 year later than light from A 4. we see the light from C (far side of object) 1/2 year later than light from B and 1 yr later than light from A - hence we see sudden flash of light spread over a full year

Question 163

Engines 2

Answer 163

1968

Question 164

Engines 2

Answer 164

1968 Bell about black holes lurking in center of galaxies - -potential energy of material falling into the black hole could be turned into radiation - -to produce the energy we see the black hole would have to be super massive - -this black hole would deb about the size of our solar system - -would explain the active galactic nuclei

Question 165

Supermassive black holes

Answer 165

Supermassive black hole would contain millions or billions of solar masses - -didn't form like a stellar black hole after a supernova - -there is strong evidence that a 2.6 million solar mass black hole lies at center of milky way - -also evidence of black holes in a number of nearby galaxies (one found by BYU) 1. material in an accretion disk spirals inward toward the black hole 2. most inward motion halts here due to conservation of angular momentum, giving accretion disk a sharp inner edge 3. only part of the infalling material reaches the black hole

Question 166

AGN's and blackhholes?

Answer 166

Could AGNs be explained by presence of black hole in their centers? - they would have to contain a black hole with a large accretion disk of matter around it - -this matter provides the fuel - -the fact that there are no nearby quasars might simply be that the fuel has run out or decreased enough to lesson the output - milky way could have been a quasar at one point

Question 167

Viewing directions - spirals - two types of seyfert galaxies

Answer 167

Type I - -have both broad and narrow spectral lines - -a more pole on view - -sees the blackhole Type II - -have only narrow emission lines - -ednge on seeing the disk

Question 168

Viewing directions - spirals - two types of seyfert galaxies

Answer 168

Type I - -have both broad and narrow spectral lines - -a more pole on view - -sees the blackhole Type II - -have only narrow emission lines - -edge on seeing the disk

Question 169

T/F spiral galaxies are thought to come from systems with steady star formation rates

Answer 169

TRUE

Question 170

What fraction of quasars are radio-loud?

Answer 170

10%

Question 171

From the hubble deep field we think that galaxies are formed from what?

Answer 171

A lot of small clouds that then merged

Question 172

T/F some nearby galaxies are quasars

Answer 172

FALSE - nearest is 750 million ly away

Question 173

Which is not necessarily an Active Galactic Nuclei

Answer 173

A grand design spiral

Question 174

T/F - We believe that all AGNs are driven by a supemassive black hole

Answer 174

TRUE

Question 175

Why is it surprising that Cygnus A is one of the 3 brightest radio sources in the sky?

Answer 175

It is coming from a galaxy 750 million ly away

Question 176

From a light time argument how large is the object that is varying in brightness in a period of 400 min?

Answer 176

about 400 light minutes acorss

Question 177

T/F radio quiet quasars tend to be associated with spiral galaxies

Answer 177

TRUE

Question 178

Why would we expect an AGN to become less active over time?

Answer 178

the amount of free material near the black hole decreases with time. this is the fuel that drives the activity, therefore the activity decreases

Question 179

What is the source of energy for an AGN?

Answer 179

conversion of potential energy as material falls toward the black hole?

Question 180

We call one group of Active Galactic Nuclei (AGNs) Quasars. What does this term represent?

Answer 180

Quasars represent two main characteristics, they have both strong radio sources and look like stars. The two characteristics combine to name the term "Quaser," from quasi-stellar and star, and AGNs are active galaxies.

Question 181

Cosmology

Answer 181

Cosmology - study of the universe: - stidu of creation, evolution, nature, fate, content of universe man has created many theories over years to explain universe - every culture has something Also many scientific theories about universe - earth centric, steady state, big bang, string theory ---there are observed phenomenon that any theory must be able to predict - also want theories that can be observed to be tested

Question 182

Nature of the universe

Answer 182

Why is the sky dark? - -question bothered Kepler - by Newton's theory of an infinite static universe it shouldn't be - sometimes called OLBER'S PARADOX - -if same if infinite and static then no matter which direction you look you should always run into some luminous object - therefore entire sky should be illuminated - -part of the solution is interstellar absorption, but doesn't work out the plane

Question 183

Bias toward a static universe

Answer 183

Many astronomers were biased toward idea of a static universe - the expanding universe was predicted by lemaitre from general relativity in 1927 - einstein inserted the Cosmological constant into general relativity to make the theory match a static universe - observationally the expansion of the universe was found by Edwin Hubble in 1920s

Question 184

Bias toward a static universe

Answer 184

Many astronomers were biased toward idea of a static universe - the expanding universe was predicted by lemaitre from general relativity in 1927 - einstein inserted the Cosmological constant into general relativity to make the theory match a static universe - observationally the expansion of the universe was found by Edwin Hubble in 1920s What does expanding mean? expanding into nothing - there is nothing outside of space - -general relativity treats space as flexible - -what is expanding - Intergalactic SPACE is expanding - galaxies are not expanding in size -regions of strong gravity are not expanding -space is rigid in these regions - -from our point of view it would deb easy to say we are the center of expansion - however every galaxy sees every other galaxy as moving away - each thinks they are the center

Question 185

Cosmological redshift

Answer 185

A photon travels through space - as it travels space expands and the photons wavelength is stretched out - -this causes the photon to become redshifted - this form of redshift called Cosmological redshift - not same thing as a doppler shift

Question 186

Assumptions in our models of the universe

Answer 186

Homogeneous - -every region is like every other region - -this is true over large regions Isotropic --if you look in diff directions you see the same things - this is a general statement together these two constitute the COSMOLOGICAL PRINCIPAL --there is no special location in space Models that obey the cosmological principle have proven successful in matching obersvation --general relativity is based on cosmological principle -we will assume a homogeneous and isotropic universe in all further discussions

Question 187

The big bang

Answer 187

From Hubble's observations we know universe is expanding Remember crab nebula - -astronomers ran the explosion back to its origin - -we can do something similar with the universe - -if we run the clock backwards we should reach a point of ultra high density - this is where model starts In 1940s Gamov made suggestion that it could have started with a HUGE explosion - 1950 Hoyle coined phrase 'big bang' to describe event - -it is interesting that Hoyle is one of few people who didn't believe in some form of big bang model Big bang is not like explosion we have on earth - -in earth explosion pieces flu off in various directions into space - if you trace pieces back you find out where original object was - -not true of big bang - big bang explosion actually carried the space and time with it

Question 188

When did big bang happen?

Answer 188

From Hubbles law we know that v: Ho d or.. (Ho = v/d) - -in big band we start with two objects moving apart: they were together when universe began - -we find To = separation distance/recessional velocity = d/v - -therefore To = 1/Ho - -if we use Ho = 72 km/sec/mpcs we find a value for the age of the universe of 13-15 billion years - this is only an estimate of age and depends on factors

Question 189

Forces in universe

Answer 189

Gravity - -masses pull on each other - -NO opposite, NO anti-gravity Strong force - -holds protons and neutrons together in nuclei of atoms - -short range - has opposites (repulsion and attraction) Electromagnetic force - -related to charged particles - -longer ranged - has opposites Weak force - -related to radioactive decay - -short range - has opposites

Question 190

GUTs

Answer 190

In 1970s it was proposed that the strong, weak and electromagnetic forces could be treated as one force - -this has proven possible in theory - -supergrand unified theory would put all 4 forces together - no one has worked out details of this theory - plays role in models of big band

Question 191

GUTs

Answer 191

In 1970s it was proposed that the strong, weak and electromagnetic forces could be treated as one force - -this has proven possible in theory - -supergrand unified theory would put all 4 forces together - no one has worked out details of this theory - plays role in models of big band

Question 192

Standard big bang model

Answer 192

Expansion starts from point and universe is hot, dense, and full of high energy photons - for very early time period the laws of physics as we know them today didn't exist - four fundamental forces split off - -at 10^-43 seconds gravity splits from other forces - -time when inflation occurred - -then we get GUT era (Grand unified theory) - lasts up to 10^-35 seconds when strong nuclear force splits off - -now we have era when particles start to exist - -created out of high energy photons - quarks and particles - -this is electroweak era (Weak nuclear force and electromagnetic forces split) - era of confinement - no free quarks - -we know quarks exist today but not alone (always in pairs or triplets) - -at this point universe is starting to fill with material more natural to us: protons, neutrons, electrons (still don't have atoms) - up to 20 min the universe is at temp like those found in centers of stars - -protons and neutrons form heavier nuclei by fusion - -all other elements wait - -beyond era of nucleosynthesis we wait for stars to go beyond first 3 elements of periodic table - from that time up to 300,000 yrs we have time with nuclei and electrons but few atoms - -universe still hot that it fills with high energy photons - -universe was radiation dominated - -backgroun temp dropped to 3000k, then atoms could start to exist - -photons free to travel through universe - cosmic microwave background - -at this point universe as we know it today can start to form first go through dark ages before first star is formed - -star and galaxies start to come into existence - -really don't have time to go into dark matter halos, formation of first stars or formation of galaxies - active areas of research

Question 193

Looking into past

Answer 193

If we accept 14 billion years as approx. age of universe, then we only see 14 billion ly into space - -light from anything more distant hasn't had time to reach us yet - -is sphere around us with 14 billion ly radius beyond which we can't see - -sphere called COSMIC PARTICLE HORIZON - the OBSERVABLE universe is located in this sphere other evidence --expansion of universe is not enough evidence of big bang - other comes from bell labs

Question 194

Looking into past

Answer 194

If we accept 14 billion years as approx. age of universe, then we only see 14 billion ly into space - -light from anything more distant hasn't had time to reach us yet - -is sphere around us with 14 billion ly radius beyond which we can't see - -sphere called COSMIC PARTICLE HORIZON - the OBSERVABLE universe is located in this sphere other evidence --expansion of universe is not enough evidence of big bang - other comes from bell labs

Question 195

Radio noise for big bang

Answer 195

Princeton, NJ at Bell telephone laboaroties - 1960 two workers Penzias and wilson were working on communication satellites - -found annoying background noise in radio signal - -noice was uniform in all directions - -nothing they could do to eliminate noise - -you can see noise today on tv if you tune to station with no signal What was noise? - Alpher and Hermann proposed big bang must have been hot - would cause reactions similar to those occurring at center of sun - in 1960s theory that amt of helium we see in universe could be formed in early universe - since universe hot should have been filled with high energy photons - -as universe expanded it cooled and high energy photons were cosmologically redshifted to longer wavelengths - blackbody curve for photons should now be redshifted into microwave region of spectrum - should have a peak defined by a temp of few degrees above absolute zero

Question 196

Cosmic microwave background

Answer 196

Design work was begun on an antenna to look for background - - workers at Princeton in Bell labs - -two bell labs stumbled on Cosmic Microwave Background without looking for it - -imrpoved observations carried out over many years since

Question 197

COBE satellite

Answer 197

Study background radiation above atmosphere a satellite was launched in 1989 - -was cosmic background explorer or COBE - plotted blackbody curve of background - -blackbody curve corresponded to a temp. of 2.726 K COBE found two variations - -first related to motion of milky way and orbit of the solar system - this causes slight red and blue shifts in background radiation - -backgroun not completely isotropic - -COBE found very small in background - likely seeds needed to build superclusters - -without variations nothing would exist in universe

Question 198

WMAP

Answer 198

Newer satellite has greater detail on temp map -WMAP project shows that universe is extremely flat - but still shows small variation needed those small variations in primordial power spectrum then grow into what we see today --models grow them to what they might look like today - this is distribution of dark matter

Question 199

When we talk about expanding universe, what is expanding?

Answer 199

space btwn galaxies is stretching

Question 200

We have seen many diff versions of redshifts this semester. What causes cosmological redshift?

Answer 200

Photons are stretched by expansion of space

Question 201

In what wavelength region do we see the CMB?

Answer 201

Microwave

Question 202

What is description of our current model of the universe?

Answer 202

Expanding space that is stretching in every direction

Question 203

What is best estimate for age of universe?

Answer 203

It is on the order of 14 billion years old

Question 204

What do we call the idea that there is no special place in the universe?

Answer 204

The cosmological principle

Question 205

What do we call the idea that there is no special place in the universe?

Answer 205

The cosmological principle

Question 206

What is cosmology?

Answer 206

``` Study of the universe --study of evolution in the universe --study of the origin of the universe --study of the content of the universe ALL OF THE ABOVE ```

Question 207

T/F we see entire universe using our telescope

Answer 207

FALSE

Question 208

Why is it important that there are fluctuations in the Cosmic microwave background?

Answer 208

There are two variations that were discovered, related to the motion of the Milky Way and the orbit of the Solar System. These fluctuations cause slight red and blue shifts in the background radiation. This tells us that the Cosmic Microwave Background is not completely isotropic, and without them nothing would exist. These fluctuations are needed to build the objects in the Universe. 10

Question 209

Why is it important that there are fluctuations in the Cosmic microwave background?

Answer 209

There are two variations that were discovered, related to the motion of the Milky Way and the orbit of the Solar System. These fluctuations cause slight red and blue shifts in the background radiation. This tells us that the Cosmic Microwave Background is not completely isotropic, and without them nothing would exist. These fluctuations are needed to build the objects in the Universe. 10

Question 210

Formation of matter

Answer 210

Matter had to be created in the universe, since it started as energetic photons -however, einstein gave us a way to get matter from energy (opposite when we talked about stars) E = mc^2

Question 211

Pair production

Answer 211

To conserve quantities we must make a particle as a particle-antiparticle pair - -the antiparticle is a form of anti-matter - -anti-matter is nothing amazing only definition - if we form a proton we must form an antiproton at same time - -if two photons of sufficient energy collide they can create a real particle-antiparticle pair - -this is called PAIR PRODUCTION - however, these particles can also collide and create two photons - process called ANNIHILATION

Question 212

Matter vs. antimatter

Answer 212

We live in matter dominated universe - little antimatter around - if material had to be created in matter-antimatter pairs, where is all antimatter? - are there still areas of antimatter running around out there? - as far as we know there is little antimatter left in universe - open questions

Question 213

Dark matter

Answer 213

We talked about rotation curves for galaxies - milky way - we don't see the edge --also talked about gravitational lensing - sometimes we can't see the mass that is causing the gravitational lens - we see something similar in the motion of galaxies within clusters of galaxies - this is difficult subject since we can't see matter

Question 214

Diff models for dark mtter

Answer 214

Astronomy based mostly on light from an object dark matter represents problem - -only seen by its gravitational effects - -even with that in mind there are diff models for dark matter (cold dark matter, warm, hot - temp here refers to motion of particles) - -current models prefer cold dark matter - still don't know what it Hot dark matter would predict that large structures formed first - --start with supercluster- break into clusters - then form galaxies - -often called top-down formation Cold dark matter uses bottom-up formation process --build smaller things like galaxies - merge into clusters, etc.

Question 215

Diff models for dark mtter

Answer 215

Astronomy based mostly on light from an object dark matter represents problem - -only seen by its gravitational effects - -even with that in mind there are diff models for dark matter (cold dark matter, warm, hot - temp here refers to motion of particles) - -current models prefer cold dark matter - still don't know what it Hot dark matter would predict that large structures formed first - --start with supercluster- break into clusters - then form galaxies - -often called top-down formation Cold dark matter uses bottom-up formation process --build smaller things like galaxies - merge into clusters, etc. the models that exist for formation of structure we see today start with building of structures in dark matter

Question 216

CMB - dark matter halos

Answer 216

Small variations in CMB - think of those as density variations -what would happen in regions that are more dense? As dark matter goes from more uniformly distributed to the pattern of filaments we see today there are denser regions - these dark matter halos are denser regions that have a gravitational influence Normal matter is drawn into dark matter halos --this could be formation of: galaxies - or early generation of stars -

Question 217

Population III stars

Answer 217

We talked about metal rich pop I stars like the sun - and metal poor stars in Pop II - -however, even those stars have more metals that would be created during big bang - where did first round of metal enrichment come from? - we don't know a lot about pop III stars Models for these stars cover wide range of masses - -some say there are 100 solar mass to 1 solar mass stars - -other models say they were all high mass stars from 60 to 300 solar masses - -some of those could still be around today

Question 218

Population III stars

Answer 218

We talked about metal rich pop I stars like the sun - and metal poor stars in Pop II - -however, even those stars have more metals that would be created during big bang - where did first round of metal enrichment come from? - we don't know a lot about pop III stars Models for these stars cover wide range of masses - -some say there are 100 solar mass to 1 solar mass stars - -other models say they were all high mass stars from 60 to 300 solar masses - -some of those could still be around today

Question 219

In what form is material created from energy in the early universe?

Answer 219

As a pair. One particle of matter with its matching anti-matter particle

Question 220

What is indirect evidence of the presence of dark matter?

Answer 220

- -Flat rotation curves of galaxies on the outer edge - -motion of galaxies within clusters of galaxies - -as gravitational lensing of distant objects

Question 221

T/F we have seen 50 pop II stars in the entire universe

Answer 221

FALSE

Question 222

What would pop III stars be made of?

Answer 222

Entirely of primordial elements created in big bang

Question 223

T/F right now our models of universe favor cold dark matter as explanation of what we see

Answer 223

TRUE

Question 224

How much anti-matter is still there in universe?

Answer 224

There is little anti-matter left relative to amount of matter

Question 225

T/F scientists believe that there are dark matter stars in the universe

Answer 225

FALSE

Question 226

Discuss development structure in universe from small initial density variations

Answer 226

Small density variations led to the formation of the universe. The more dense regions are dark matter halos that have a gravitational influence. This initiates the formation of galaxies or population III stars. Population III stars are metal poor, made only out of primordial elements

Question 227

Discuss development structure in universe from small initial density variations

Answer 227

Small density variations led to the formation of the universe. The more dense regions are dark matter halos that have a gravitational influence. This initiates the formation of galaxies or population III stars. Population III stars are metal poor, made only out of primordial elements

Question 228

What is fate of universe?

Answer 228

From hubble law we know that universe is currently expanding - in 1910 hubble also discovered something else about expansion, it was slowing down - gravity was trying to pull everything back together - how fast is it slowing down - what is deceleration rate?

Question 229

Gravity's pull

Answer 229

If i launch rocket off surface of earth three things can happen to that rocket - 1. it escapes earth's gravity - 2. it has just enough velocity to move away an finally escape at time = infinity - 3. it will fall back to earth same rules apply to universe as a whole

Question 230

Critical density

Answer 230

Fate of universe is based on mass, or density of the universe - -to just close the universe we would need the critical density: Pc - -with an Ho: 72 km/s/mpc tho gives Pc = 1.1 x 10^-26 kg/m^3 - -this doesn't sound like much, but remember there is a lot of empty space out there

Question 231

Density parameter

Answer 231

Some people prefer to use other variables to describe universe - -some use density parameter - measured fraction of critical density - final parameter is the deceleration pare mater

Question 232

Various fates

Answer 232

unbound or open universe expands forever - has enough velocity to escape gravity (p Pc) - could start new universe Which is correct?

Question 233

Recessional velocity vs. distance

Answer 233

We can take look at distance galaxies and plot recessional velocity vs distance - --based on various models we should see diff effects in the distant past - we will start with older ideas to introduce ideas and then move on to current data Distance on x axis increasing ^^ and recessional velocity on y xis increasing --> - -if expanding more slowly in past and sped up it goes straight then curves up - -constant rate - -universe expanded rapidly in past sow expansion slows down and increases velocity as distance decreases

Question 234

Results of data graphs

Answer 234

Puts new twist on older models - -talked about deceleration, but now data makes it look like an acceleration - -leads to more complex models - -current theory favors an one universe - but data is still right on the line and we are very close to critical density - -may never know for sure which is correct

Question 235

Dark energy

Answer 235

To get an acceleration would require something so push - --some energy we don't see - -dark energy

Question 236

Effects of a closed universe

Answer 236

Eventually universe would stop expanding - -galaxies would begin to be blue shifted as universe contracted - -backgroun temp would rise - -at 70 million years to go the galaxies would crowd together to make night sky bright - at 1 million years the temp would reach 3000 k and atoms would be destroyed - -in the end the big crunch would occur and we will return to Cosmic singularity - in theory this would start entire process over

Question 237

Effects of open universe

Answer 237

Other extreme is universe will expand forever - -galaxies will collapse as will cluster of galaxies to form gigantic black holes - -even black holes don't last forever, they evaporate - -Hawking said the smaller the black hole the faster it evaporates -called hawking process or hawking radiation - very slow - -but in a universe that expands forever there is time to evaporate - -as largest black holes evaporate the process speeds up - eventually they will just pop back into normal space-time - -Hawking has predicted primordial black hold which we should see these pop - -this is something that has not been seen in observations at this point in time

Question 238

Effects of open universe

Answer 238

Other extreme is universe will expand forever - -galaxies will collapse as will cluster of galaxies to form gigantic black holes - -even black holes don't last forever, they evaporate - -Hawking said the smaller the black hole the faster it evaporates -called hawking process or hawking radiation - very slow - -but in a universe that expands forever there is time to evaporate - -as largest black holes evaporate the process speeds up - eventually they will just pop back into normal space-time - -Hawking has predicted primordial black hold which we should see these pop - -this is something that has not been seen in observations at this point in time

Question 239

T/F as of 2002 we know the ultimate face of the universe?

Answer 239

FALSE

Question 240

In what kind of universe would we expect to see the evaporation of black holes?

Answer 240

expanding universe

Question 241

During this semester we have talked mostly about objects made of normal matter. This is what we call baryonic material and it is mostly composed of elements from the periodic table and electrons. We now talk about things like Dark Matter and Dark Energy. About what percentage of material in the Universe do we believe to be in the form of normal matter (baryonic matter)

Answer 241

4%

Question 242

what do scientists believe is causing the acceleration in the universe?

Answer 242

dark energy

Question 243

T/F we have seen primodal black holes pop back into normal space by hawking process

Answer 243

FALSE

Question 244

T/F it is possible for universe to collapse and start over

Answer 244

TRUE

Question 245

What is current state of our universe? - what is universe doing right now

Answer 245

Accelerating

Question 246

What makes up largest part of composition of the universe

Answer 246

Dark energy

Question 247

What makes up largest part of composition of the universe

Answer 247

Dark energy

Question 248

Radio observations of life

Answer 248

Radio astronomy found many organic and carbon based compounds in space Stanley Miller and Urey attempted to match the early env. of the earth - -mixed water, Co2, N2, and H2 - -plus energy in form of lightning - -produced reddish-brown substance rich in amino acids, but this is not life - -modern versions of experiment have produced other compounds - -science has NEVER created life in a test tube

Question 249

SETI

Answer 249

Search for extra-terrestrial intelligence - -often revolves around radio telescopes listening for messages or noise from other planets - -remember discovery of pulsars? - in SETI they generally look through 'water hole' to minimize noise level - -currently they target G-type stars like sun - listen for emissions coming from these regions - -to date there have been 4o unsuccessful searches Two possible reasons - -no one is out there - -they are there but too far away for us to hear

Question 250

Habitable zone

Answer 250

Not all stars are the same for supporting life | --to support life like that found on earth that planet must be in HABITABLE ZONE

Question 251

Drake's equation

Answer 251

To try and put numbers on problem we use equation by Frank Drake - -using simple numbers this equation estimates the number of advance civilizations - -based on simple probabilities - -

Question 252

Drake's equation

Answer 252

To try and put numbers on problem we use equation by Frank Drake - -using simple numbers this equation estimates the number of advance civilizations - -based on simple probabilities N = R*fp nc fl fi fc L N - # tech advanced civilizations in our galaxy R* - rate of solar-type star formation fp - fraction with planets nc - # planets per star suitable for life fl - fraction on which life arose fi - fraction that evolved intelligent species fc - fraction that survive to sufficient tech L - life time of that civilization Let all numbers be 1 Let L = 100 years Let N = 100 civilizations in our galaxy --the disk in our galaxy has 1,480,000,000 cubic ly -each civilization as 14,800,000 cubic ly to itself --this is box 245 ly on a side therefore nearest intelligent life would be 245 ly away

Question 253

LDS astronomers

Answer 253

LDS astronomers also general authorities - only one: Orson Pratt - -number General authorities that have been scientists - -currently large growth of LDS astornomers

Question 254

Orson Pratt

Answer 254

Sept. 1811 in Hartford NY - -baptized sept 1830 (on bday) - -during youth attend school occasionally but self taught in math and science - -attend school of prophets at Ohio - 1835 at age 24 called to Quorom of 12 apostles - crossed plains with first pioneer family making scientific measurements on way - -first to enter SLC valley - prof math, astronomy, moral science at University Deseret - on trail to SL saw Jupiters 4 moons through telescope - several lectures in SL tabernacle on astronomy

Question 255

Orson Pratt

Answer 255

Sept. 1811 in Hartford NY - -baptized sept 1830 (on bday) - -during youth attend school occasionally but self taught in math and science - -attend school of prophets at Ohio - 1835 at age 24 called to Quorom of 12 apostles - crossed plains with first pioneer family making scientific measurements on way - -first to enter SLC valley - prof math, astronomy, moral science at University Deseret - on trail to SL saw Jupiters 4 moons through telescope - several lectures in SL tabernacle on astronomy

Question 256

Meridian house (orson pratt observatory)

Answer 256

Build within walls of temple square 1860 when walls of temple no more than 5 ft high - -built and likely called SL observatory - -bc long night spent in observatory became known as Orson's observatory - he had 3" telescope brought from england and chronometer - set up survey plan outside temple square to mark point for baselines and meridians for Jefferson land ordinance - gov. started from this point to define utah territory - designated Great Salt Lake baseline and Meridian

Question 257

Meridian house (orson pratt observatory)

Answer 257

Build within walls of temple square 1860 when walls of temple no more than 5 ft high - -built and likely called SL observatory - -bc long night spent in observatory became known as Orson's observatory - he had 3" telescope brought from england and chronometer - set up survey plan outside temple square to mark point for baselines and meridians for Jefferson land ordinance - gov. started from this point to define utah territory - designated Great Salt Lake baseline and Meridian Observatory stood on Temple square for 25 years and quietly dismantled upon temple's completion

Question 258

Diff btwn Salt lake and Nauvoo temples

Answer 258

Moonstones in SL temple at a variety of phases - -50 moonstones around temple, one for each moon phases of year 1878 - -sequence starts with due north stone and proceeds clockwise around temple - -50 earthstones also to show earth rotating through week - -saturn stones were to be well defined but carving too difficult - big dipper on SL temple

Question 259

Diff btwn Salt lake and Nauvoo temples

Answer 259

Moonstones in SL temple at a variety of phases - -50 moonstones around temple, one for each moon phases of year 1878 - -sequence starts with due north stone and proceeds clockwise around temple - -50 earthstones also to show earth rotating through week - -saturn stones were to be well defined but carving too difficult - big dipper on SL temple

Question 260

T/F search to find alien civilization called SETI

Answer 260

TRUE

Question 261

T/F living organism have been created in a test tube from basic atmospheric materials

Answer 261

FALSE

Question 262

Where would we expect the habitable zone to be around a M star

Answer 262

Closter tot he star than the earth is from the sun

Question 263

Out of fractions included in drake equation is the fraction of civilizations revived to be tech advance. Why would this be necessary for searches made by SETI?

Answer 263

They need to have radio communications that leak into space that we can detect with radio telescopes

Question 264

Why would an advanced civilization around an O star be less likely?

Answer 264

the main sequence life of an O star is too short for an advanced civilization to arise

Question 265

What region of sky did orson pratt say was 'unorganized matter enough for many millions of world as large as the sun?

Answer 265

Orion - and he was correct

Question 266

T/F there was once an observatory not temple square in SLC

Answer 266

TRUE

Question 267

A portion of which constellation appears on west face of SL temple

Answer 267

Ursa Major

Question 268

How many moonstones are there around SL temple?

Answer 268

50

Question 269

How many moonstones are there around SL temple?

Answer 269

50

Question 270

Galaxy song distances and sizes

Answer 270

Our galaxy contains a 100 million stars - -100,000 ly side to side - bulges in middle 16,000 ly thick - -but out by us is 3000 ly wide We're 30,000 ly from galactic central point - -we go round every 200 million years - -our galaxy is one of millions and billions Universe keeps expanding --speed of light is 12 million miles a minute - fastest speed there is