Final section Flashcards
Galileo and the early days
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?
Nebula
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
Two camps about spiral nebula
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
Debate into the 1920s
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
Entrance of Edwin Hubble
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
Distance of M31
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
Spiral nebula to spiral galaxies
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
The earth’s place in the milky way
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)
The earth’s place in the milky way
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
Kapteyn’s attempt
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
Trumpler’s discovery
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
The globular clusters
in 1910s Harlow Shapley looked out of the plane to see the globular clusters
Shapley and the globular clusters
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
Infrared observations
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
Size of the Milky way (disk, central bulge, halo)
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
The halo
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
The bulge region
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
The disk
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
More than one disk
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
A closer look at the disk
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
The spiral of arms
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
The spiral of arms
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
Galaxy rotation
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
Galaxy rotation
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
Orbit of the sun
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
Kepler’s law
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
Mass inside the sun
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
Where is the edge?
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
The missing mass
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
The heart of the milky way
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
How was Shapley-curtis debate settled?
Edwin Hubble found the distance to M31 and it was far outside the size of the milky way as determined by Shapley
The time is takes the sun to orbit the center of the milky way
220 million years
The thickness of the thin disk
1000 lightyears
the diameter of the milky way
100,000 to 160,000 lightyears
the mass inside the suns orbit
9.0 x 10^10 solar masses
the distance from the sun to the center of the milky way
26,000 lightyears
the thickness of the thick disk
3000 lightyears
the estimated total mass of the milky way
6.0 x 10^11 solar masses
the mass of the central black hole of the milky way
3.7 x 10^6 solar masses
the distance to M31, the nearest large galaxy
2.2 million lightyears
What objects are used to determine the distance of M31
Cepheid variable
What do we believe to be in the middle of the milky way galaxy
a massive black hole
How many arms does the milky way have
4
T/F - The results of herschel and Kapteyn were both biased due the the existence of interstellar extinction
TRUE
What do we use to map the shape of the spiral arms of the milky way?
21 cm radiation from neutral hydrogen
What do we use to map the shape of the spiral arms of the milky way?
21 cm radiation from neutral hydrogen
Diff types of galaxies
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
Elliptical Galaxies - E
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
Structure of elliptical galaxies
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
Giant elliptical galaxies
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
Giant elliptical galaxies
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
Dwarf elliptical galaxies
Not much larger than a globular cluster
- -some as small as 1 kpc in diameter
- -smallest contain only about 10^5 solar masses
Dwarf elliptical galaxies
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
What happens if we flatten a elliptical to a disk
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)
Spiral galaxies
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
Spiral galaxies
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
Sa galaxies
These are spiral galaxies with:
- a large bulge
- tightly wound arms
Sb galaxies
Spiral galaxies with
- moderate bulge
- looser arms
Sc galaxies
Spiral galaxies with
- small bugle
- very loose arms
What are the arms?
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
Density waves in the galaxies
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
Problems with the density-wave model
(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
Grand design vs. Flocculent
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
Final class of galaxies - irregular galaxies
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
Edwin Hubble and Vesto Slipher
In
Edwin Hubble and Vesto Slipher
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)
Hubble expansion
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
Hubble Law
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
Measurement of Ho in Hubble law
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
Problems with the hubble law
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
Problems with the hubble law
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?
The milky way’s group
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
Large rich clusters
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
Is there anything larger than a cluster?
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
Is there anything larger than a cluster?
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
Voids
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
Other features seen in maps of galaxies
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
Missing mass again
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
Missing mass again
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
What are the largest galaxies we see?
Giant elliptical galaxies
How do we think giant elliptical galaxies got so large?
By galaxy cannibalism - they ate smaller galaxies
What are most commonly observed galaxies in the universe
Spiral galaxies
Which type of galaxies are most common?
dwarf galaxies
T/F we think the majority of irregular galaxies come from collisions
TRUE
T/F All galaxies start out as EO galaxies and proceed along the Hubble Fork over time
FALSE
T/F galaxies with tight, narrow arms are formed by self-propagating star formation
FALSE
-self propagating star formation tends to move in random directions and therefore wouldn’t produce tight, well defined spiral arms
Discuss the meaning of Hubble Law
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.
Disucc the structures larger than a galaxy that we find in the universe
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.
Disucc the structures larger than a galaxy that we find in the universe
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
Theory of relativity
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
Special theory of relativity
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
Two principles of special theory of relativity
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
Newtonian motion
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
Motion of light
Astronaut with flashlight:
light 3x10^8 m/s —>
Astronaut flying in spaceship
1 x 10^0 m/s
New way of thinking
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
Lorentz transformations
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?
Tests of special relativity
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
Other principles (relativity)
- -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
General theory of relativity
Published in 1915 by Einstein
General theory of relativity
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
Curved space-time
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
- massive object curves the space-time around us
- far from the object, space-time is nearly “flat”, close to the object, the curvature forms a “Well”
- in Einsten’s picture of gravity other objects sense the curvature and are drawn into the “well”
What can we predict from general relativity?
The motion of the planets
the blending of light
The precession of mercury
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
The bending of light
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
The bending of light
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
Escape of light
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
Gravitational redshift
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
Gravitational waves
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
Relativity
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
Relativity
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
Effects of general relativity
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
Neutron stars
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
Black hole
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
Curvature of space
- Black hole sharply curves the space-time around it
- far from the black hole space-time is nearly “flat” close to the black hole, the curvature forms a “well” that is infinitely deep
- objects that venture too close to the black hole cannot escape from the “well”
The event horizon
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
The singularity
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
Linearity of time
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
Cosmic censorship
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
Cosmic censorship
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
Science fiction and black holes
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
Crossing the event horizon
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
Two types of black holes
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)
Schwarzchild black hold
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
Kerr black hole
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
Kerr black hole
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
Evidence of black holes
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
Cygnus X-1
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
related ideas to general relativity
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?
The wormhole
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”
The wormhole
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”
What applies to the Special theory of Relativity
- -time runs slower
- -lengths get shorter in the direction of motion
- -mass increases at higher velocity
Of the four major predictions of general relativity, for which one do we not have a direct measurement?
gravitational waves
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)
460 nm
T/F passing through a wormhole it is possible to go back in time?
TRUE - it connects two points in spacetime
What do we call the surface where the escape velocity equals the speed of light?
The event horizon
If the sun were to instantly become a black hole, what would happen to solar system?
The planets, and everything else, would maintain their current orbits
T/F we have mentioned the problem of dark matter before. The bending of light can show us the presence of dark matter?
TRUE
If i have two black h oles and the first has twice the mass of the second, which is true?
The radius of the event horizon for the first is twice as big as the second
What is an effect of gravitational lensing
- -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
T/F according to general relativity it is impossible for there to be alternative universes
FALSE
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
FALSE - it is also possible that an acceleration has happened
Describe motion on a curved surface - use proper terminoloy
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.
Early galaxies
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
Clues to the mystery of galaxy formation
- -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
Rate of star formation
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
Rate of star formation
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
Strange objects - (Quasars - early galaxies?)
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
Strange objects - (Quasars - early galaxies?)
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
Spectrum of Cyg A
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?
3C catalogue
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
Mystery to 3C 48 and 273
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)
Quasars
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
Quasar redshifts
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
Clues to the nature of quasars
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
Clues to the nature of quasars
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
Closer quasars?
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
Seyfert galaxies
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
Radio galaxies
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
Head-tail radio sources
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
Blazars
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
Engines of blazars
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
Light time arguments
- an object 1 light year across emits a sudden flash of light
- first light that we receive comes from A (the part of the object nearest to earth)
- 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
- 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
Engines 2
1968
Engines 2
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
Supermassive black holes
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)
- material in an accretion disk spirals inward toward the black hole
- most inward motion halts here due to conservation of angular momentum, giving accretion disk a sharp inner edge
- only part of the infalling material reaches the black hole
AGN’s and blackhholes?
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
Viewing directions - spirals - two types of seyfert galaxies
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
Viewing directions - spirals - two types of seyfert galaxies
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
T/F spiral galaxies are thought to come from systems with steady star formation rates
TRUE
What fraction of quasars are radio-loud?
10%
From the hubble deep field we think that galaxies are formed from what?
A lot of small clouds that then merged
T/F some nearby galaxies are quasars
FALSE - nearest is 750 million ly away
Which is not necessarily an Active Galactic Nuclei
A grand design spiral
T/F - We believe that all AGNs are driven by a supemassive black hole
TRUE
Why is it surprising that Cygnus A is one of the 3 brightest radio sources in the sky?
It is coming from a galaxy 750 million ly away
From a light time argument how large is the object that is varying in brightness in a period of 400 min?
about 400 light minutes acorss
T/F radio quiet quasars tend to be associated with spiral galaxies
TRUE
Why would we expect an AGN to become less active over time?
the amount of free material near the black hole decreases with time. this is the fuel that drives the activity, therefore the activity decreases
What is the source of energy for an AGN?
conversion of potential energy as material falls toward the black hole?
We call one group of Active Galactic Nuclei (AGNs) Quasars. What does this term represent?
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.
Cosmology
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
Nature of the universe
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
Bias toward a static universe
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
Bias toward a static universe
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
Cosmological redshift
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
Assumptions in our models of the universe
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
The big bang
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
When did big bang happen?
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
Forces in universe
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
GUTs
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
GUTs
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
Standard big bang model
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
Looking into past
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
Looking into past
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
Radio noise for big bang
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
Cosmic microwave background
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
COBE satellite
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
WMAP
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
When we talk about expanding universe, what is expanding?
space btwn galaxies is stretching
We have seen many diff versions of redshifts this semester. What causes cosmological redshift?
Photons are stretched by expansion of space
In what wavelength region do we see the CMB?
Microwave
What is description of our current model of the universe?
Expanding space that is stretching in every direction
What is best estimate for age of universe?
It is on the order of 14 billion years old
What do we call the idea that there is no special place in the universe?
The cosmological principle
What do we call the idea that there is no special place in the universe?
The cosmological principle
What is cosmology?
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
T/F we see entire universe using our telescope
FALSE
Why is it important that there are fluctuations in the Cosmic microwave background?
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
Why is it important that there are fluctuations in the Cosmic microwave background?
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
Formation of matter
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
Pair production
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
Matter vs. antimatter
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
Dark matter
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
Diff models for dark mtter
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.
Diff models for dark mtter
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
CMB - dark matter halos
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
-
Population III stars
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
Population III stars
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
In what form is material created from energy in the early universe?
As a pair. One particle of matter with its matching anti-matter particle
What is indirect evidence of the presence of dark matter?
- -Flat rotation curves of galaxies on the outer edge
- -motion of galaxies within clusters of galaxies
- -as gravitational lensing of distant objects
T/F we have seen 50 pop II stars in the entire universe
FALSE
What would pop III stars be made of?
Entirely of primordial elements created in big bang
T/F right now our models of universe favor cold dark matter as explanation of what we see
TRUE
How much anti-matter is still there in universe?
There is little anti-matter left relative to amount of matter
T/F scientists believe that there are dark matter stars in the universe
FALSE
Discuss development structure in universe from small initial density variations
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
Discuss development structure in universe from small initial density variations
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
What is fate of universe?
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?
Gravity’s pull
If i launch rocket off surface of earth three things can happen to that rocket
- it escapes earth’s gravity
- it has just enough velocity to move away an finally escape at time = infinity
- it will fall back to earth
same rules apply to universe as a whole
Critical density
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
Density parameter
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
Various fates
unbound or open universe expands forever - has enough velocity to escape gravity (p Pc) - could start new universe
Which is correct?
Recessional velocity vs. distance
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
Results of data graphs
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
Dark energy
To get an acceleration would require something so push
- –some energy we don’t see
- -dark energy
Effects of a closed universe
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
Effects of open universe
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
Effects of open universe
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
T/F as of 2002 we know the ultimate face of the universe?
FALSE
In what kind of universe would we expect to see the evaporation of black holes?
expanding universe
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)
4%
what do scientists believe is causing the acceleration in the universe?
dark energy
T/F we have seen primodal black holes pop back into normal space by hawking process
FALSE
T/F it is possible for universe to collapse and start over
TRUE
What is current state of our universe? - what is universe doing right now
Accelerating
What makes up largest part of composition of the universe
Dark energy
What makes up largest part of composition of the universe
Dark energy
Radio observations of life
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
SETI
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
Habitable zone
Not all stars are the same for supporting life
–to support life like that found on earth that planet must be in HABITABLE ZONE
Drake’s equation
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
- -
Drake’s equation
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 = Rfp 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
LDS astronomers
LDS astronomers also general authorities - only one: Orson Pratt
- -number General authorities that have been scientists
- -currently large growth of LDS astornomers
Orson Pratt
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
Orson Pratt
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
Meridian house (orson pratt observatory)
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
Meridian house (orson pratt observatory)
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
Diff btwn Salt lake and Nauvoo temples
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
Diff btwn Salt lake and Nauvoo temples
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
T/F search to find alien civilization called SETI
TRUE
T/F living organism have been created in a test tube from basic atmospheric materials
FALSE
Where would we expect the habitable zone to be around a M star
Closter tot he star than the earth is from the sun
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?
They need to have radio communications that leak into space that we can detect with radio telescopes
Why would an advanced civilization around an O star be less likely?
the main sequence life of an O star is too short for an advanced civilization to arise
What region of sky did orson pratt say was ‘unorganized matter enough for many millions of world as large as the sun?
Orion - and he was correct
T/F there was once an observatory not temple square in SLC
TRUE
A portion of which constellation appears on west face of SL temple
Ursa Major
How many moonstones are there around SL temple?
50
How many moonstones are there around SL temple?
50
Galaxy song distances and sizes
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
