Type 1a supernovae
a white dwarf steals matter from a companion star, and the white dwarf's mass slowly increases until it exceeds 1.4 M. and explodes
High z supernovae results
1996-indicated the universe wasnt slowing down as expected, but accelerating
1998-results supported this
present day-more results support this
some form of repulsive gravity or pressure that is causing the Universe to expand more and more rapidly over time
what year did Einstein propose an anti-gravity cosmological constant to keep the universe in a steady state?
dark matter end to the universe
dark matter dominates cosmic slowdown--acceleration tapers of, ending in a "Big Crunch"
dark energy end to the universe
acceleration gets stronger and eventually rips the universe apart in a "Big Rip"
in cosmology, the peculiar circumstance that the early universe must have contained almost exactly the right amount of matter to make space-time flat
as the universe gets older, light from more and more distant sources makes its way to earth, thus the size of the ______ increases over time
One of the problems of cosmology solved by the inflationary theory: why the Universe has the same average temperature in all directions, even though widely separated regions could never have been in thermal equilibrium with each other since they are beyond each other's horizons.
inflation as a solution
after inflation, the observable universe is so stretched that it appears flat to all measurements--it demands that Ω = 1.
it will collapse
if the density of the universe is higher than the critical density, what will happen to the universe?
it will expand forever
if the density of the universe is lower than the critical density, what will happen to the universe?
400-800 million years after Big Bang (much earlier than everyone thought they would star forming)
when did galaxies start forming?
Sloan Digital Sky Survey
goal is to measure the brightness of 100 million objects, and map the distances and positions of 1 million galaxies and 100,000 quasars. Still working on this survey today
would mean that the most distant galaxies would move away the fastest, less massive galaxies would move away faster, most massive galaxies would be closest to earth, and earth would be located at "ground zero" of the explosion
would mean the most distant galaxies would move away the fastest, there would be no dependence between a galaxy's recessional velocity and its mass, there would be a random distribution of galaxy masses, and every galaxy will see every other galaxy moving away
myth about light
light loses energy as it travels across the universe, the loss of energy creates redshifts, distant galaxies only appear to be moving away from us, therefore the universe would not be expanding
(1929) Zwicky hypothesized this as an alternative to the idea of an expanding universe wherein light loses energy as it travels (its wrong)
problems with tired light
if light were colliding with something (and slowing down), we should be able to tell, and its hard to imagine a non-expansion process that would redden all wavelengths equally, cant explain CMB, cant explain chemical abundances found in the universe, cant explain the formation of structures in the universe
supernova duration stretching
distant supernovae really do seem to last longer than nearby supernovae, which is what the Big Bang predicts
steady state predictions
the Hubble constant is truly constant (the universe is always expanding at the same rate), the universe had no Big Bang (its infinite in age), no matter how far back in time you go the universe was never zero in size
steady state idea
new matter is created as the universe grows so that the density of the universe remains the same over time, a "creation" or "C-field is responsible for making new matter, the amount of new matter needed isnt large, the jets observed around quasars/neutron stars/black holes could be sites of matter creation
MOdified Newtonian Dynamics; "inventing" dark matter to explain observations like the rotation curves of spiral galaxies is troubling to some astronomers--we might not understand gravity as well as we could, and therefore have no need for dark matter
MOND gravity theory
(1981) says that all stars in a galaxy should orbit at the same speed, and no dark matter is required. Mordehai Milgrom observed this. Explains galactic rotation curves, but isnt good at explaining things like the "bullet cluster"
evidence for dark matter
motions of galaxies in clusters, rotation curves of galaxies, hot x-ray emitting gas in galaxy clusters, gravitational lensing by galaxy clusters
When massive objects bend space and time enough to create multiple images of an object located behind them.
The building up of heavier elements from lighter ones by nuclear fusion (occurs in stars and during supernovae explosions).
(1930's) deduced that there must be some kind of unseen matter whose gravity holds the galaxies in clusters.
mass to light ratio (M/L)
the measure of how much unseen matter is present compared to the visible luminous matter
evidence for dark matter
motions of galaxies in clusters, rotation curves of galaxies, hot x-ray emitting gas in galaxy clusters, gravitational lensing by galaxy clusters
a hypothetical form of matter that is believed to make up 90 percent of the matter in the universe. doesnt interact with light.
MAssive Compact Halo Objects, baryonic matter living in the halo of our galaxy that we dont easily see. Ex: brown dwarfs, dead stars, and massive black holes
neutral particles with high energies but almost zero mass, there should be lots of them leftover from the Big Bang
Weakly Interacting Massive Particles, a new kind of non-baryonic particle. Ex: supersymmetric particles, axions, kaluz-klein dark matter
the Universe today is clumpy; if the ultra-smooth CMB is linked to todays universe, shouldnt there be some clumpiness in the CMB? otherwise, where did the galaxies come from?
a flammable, poisonous gas on Earth and in interstellar clouds that can be used to detect CMB
rapid expansion of the early universe will drive compression waves, or _____, through the universe, which we can measure by studying the bumps in the CMB
by studying the relative intensity of these, we can work backwards to determine the properties of the universe at decoupling
Event in the early universe when atoms first formed, and after which photons could propagate freely through space.
hydrogen was built into deuterium-->deuterium was destroyed in a reverse reaction-->universe cooled over time, and more deuterium survived long enough to form helium-->a bit of helium formed lithium. Couldn't really build any elements more complex than lithium because the universe had cooled so much that nuclear reactions began to slow
Big Bang nucleosynthesis
observed chemical abundances in early stars/galaxies constrain Big Bang models, so depending on the conditions of the early universe, different chemical abundances will result
youngest stars, most stars in Milky Ways disk, stars like our sun that are abundant in metals
the first generation of stars, contain virtually no metals, only a few have been observed
careful analysis of ________ in distant galaxies leads to measurements of H, D, He, and Li in the early universe.
around 400,000 years AB, the Universe cooled enough to allow protons and electrons to come together to form hydrogen atoms, making the universe transparent for the first time
a red shifted side and blue shifted side in the CMB, due to the motion of the earth with respect to the CMB. proved that the CMB was not in the earths atmosphere, and allowed astronomers to measure the speed of the Milky Way through space
Big Bang theory
claims that nearly all of the matter in our universe (neutrons, protons, H, He...) was created in the first 3 minutes after the Big Bang.
the four forces
strong nuclear force, electromagnetic force, weak nuclear force, gravity (in order of strength from strongest to weakest)
(1938) discovered by Hans Bethe, the fusion reactions by which stars convert hydrogen to helium, usually occur in stars the size of the Sun or smaller
the earliest universe was dominated by light (radiation). at first the universe was so hot that any particles that happened to form were immediately destroyed, but as the universe expanded/cooled, the radiation lost energy. so, particles could survive for longer and longer periods of time
quantum gravity era
current physics cant explain it, but its when matter, light, and energy coexisted in a kind of primordial soup. all four forces were united. ended with symmetry breaking.
a process in which gravity "froze out" of the cooling primordial soup. ended the quantum gravity era
the grand unified era
during this era, the electromagnetic, strong, and weak forces were united. gravity was distinct. this era ended when the strong nuclear force "froze out" of the mixture
when the universe went through a stunning growth spurt--got 1 googol times bigger WOW! no one is sure why it happened.
when free quarks roamed the universe, interacting with protons and other particles in violent matter/antimatter reactions. during this era, electromagnetism and the weak force seperated, so the four forces were distinct
when the universe cooled enough that free quarks condensed together to form hadrons (like mesons and baryons)
when all antimatter had been wiped out in reactions with matter, and protons greatly outnumbered baryons
quantum gravity era-->grand unified era-->inflationary era-->quark era-->hadron era-->lepton era (QGIQHL)
the minimum velocity needed to escape a gravitational field, outward energy vs. inward gravity
in which universe could you see the back of your own head if you could look out far enough into space?
age = 1/H0 is only true in a totally empty universe. in fact, the gravity between all the stuff in the universe should be slowing down the expansion of the universe
the true age is less than 1/H0
if the universe is slowing down, how does the true age of the universe compare to 1/H0?
________ this could make an open or flat universe expand even faster, or make a closed universe into an open universe
(1868-1921) one of the Harvard College Observatory "calculators" (along with Annie Jump Cannon). Discovered that there is a relationship between the period of a Cepheid variable star and its luminosity.
cepheid variable stars
stars whose luminosity varies ("variable stars") in a regular, predictable, periodic way.
if you know the period of a Cepheid variable star, then you can determine its average luminosity!
cosmological distance ladder
radius of the earth-->distance to the moon-->distance to the sun-->parallax of stars-->"spectroscopic parallax"-->star clusters-->cepheid variables-->supernovae in galaxies-->Hubbles law of redshifts
he discovered that galaxies are moving away from each other. Found Hubble constant which can give the age of the universe
A mathematical quantity that describes the changing separation of two points as the Universe expands
when the universe expands, light waves also expand to longer wavelengths (when wavelengths stretch between two points, so does space) causing a redshift
(276-194 BC) a mathematician, geographer, and the third librarian of Alexandria, devised an early leap-year calendar, and wrote On the Measurement of the Earth
William Herschel's sister who discovered 8 comets, many nebulae, and was one of the first women elected into the Royal Society
William Herschel's son who carried on his fathers work to chart nebulae in the southern hemisphere
discovered stellar parallax when he measured a parallax from Vega, which was the first distance measurement ever made to an object outside our solar system
man who measured another parallax, which was the second distance measurement ever made to an object outside our solar system
machine whose mission was to map the motions of 120,000 stars. Shutdown in 1993, but mapped lots of stars
Global Astrometric Interferometer for Astrophysics. Its a Planned European Space Agency satellite, which will measure the positions and Doppler shifts of 1 billion stars with crazy precision. Scheduled for launch in 2013
spherical groupings of tens of thousands of stars. contain so many stars that they can be seen at much larger distances than single stars. About 150 are known in the Milky Way
(1914-1918) studied globular clusters at Mt. Wilson observatory. Determined their sizes and distances and made a 3D map of their positions from Earth. This map revolutionized the way people thought about the Milky Way.
"Cosmological Considerations on the General Theory of Relativity"
(1917) Einsteins book in which he applied GR to the universe. Found that GR predicted that the universe cannot be static--it must either expand or contract. Included the cosmological constant
states that most galaxies are moving away from the Earth. The more distant a galaxy is, the faster it moves away from us.
the spreading out of space--space expands evenly between all objects. Objects initially at large distances will recede faster than objects initially nearby. There is no center to the expansion! (Picture a balloon being blown up)
(1894-1966) Belgian priest and physicist who realized that GR argued for an expanding universe. His work was ignored until Hubble's 1929 discovery of the expanding universe. He also realized that an expanding universe implied a beginning to the universe
planet or brown dwarf (never becomes a star)
what is the fate of a star that is less than 0.08 M. (solar mass)?
aka event horizon; the border between the black hole and the rest of the universe- the "point" of no return
the boundary that marks the "point of no return" between a black hole and the outside universe
the idea that everything can be foretold if the starting conditions are known in enough detail
special relativity, photoelectric effect, Brownian motion, GR, "Cosmological Considerations on the General Theory of Relativity"
Theory that motion can be measured only relative to some particular observer. Predicts that nothing can travel faster than light in a vacuum, there are no privileged reference frames, "simultaneity" is different for observers moving with respect to each other, time slows down for moving clocks, lengths contract along the direction of motion for moving objects, mass increases for moving objects, and matter and energy are =
things created when cosmic rays strike high in the Earths atmosphere. Live only about 2.2 millionths of a second, but they still reach the surface of the earth due to the predictions of relativity!
time and space vary depending on the motions of the observers, but c is ALWAYS constant. Matter and energy are interchangeable. Nothing can travel faster than the speed of light.
states that gravity is nothing more than curvature of spacetime. All matter (and energy) curves space and massive objects causes a greater curvature
Annie Jump Cannon
(1843-1941) worked at Harvard College Observatory cataloging 350,000 stellar spectra. She cataloged 5000 stars per month. Reorganized spectra according to their temps.
what is the single most important factor that determines what a star's spectrum looks like?
one with a smaller mass
which star will live longer--one with a larger mass or one with a smaller mass?
objects that have a well-known luminosity. Ex: supernovae (especially Type 1a), any star whose spectrum can be measured (especially giants and supergiants), and Cepheid variable stars
weak anthropic principle
the idea that the conditions that we observe in the universe must be compatible with our own existence
strong anthropic principle
the idea that the universe was created as it was in order for us to be here now; the "purpose" of the Universe is to create life
Perfect Cosmological Principle
the universe is the same in all directions and places at all times (this isnt true yo)
the white dwarf with the greater mass
which would have a smaller radius--a white dwarf with a smaller mass or with a greater mass?
how to measure the mass of a star
study the orbits of planets around the star and study the motion of the stars binary companion (if it has one)
properties include they can emit more energy than all the rest of the stars in a galaxy combined, they can be observed from huge distances, elements heavier than iron are created during their explosions, and material is ejected at HUGE HUGE speeds
predicted by Baade, Zwicky, Harrison, Wheeler, and others. Collapsed, SUPERdense core of a star supported by neutron degeneracy pressure
what is the upper limit on the original mass of a star that could later become a neutron star?
(1968) graduate student who discovered some objects that emitted very strong, periodic radio pulses.
model of pulsars where a star rotates around, and appears to flash light with every rotation
structure of a 1 M. star
H fuses to He in the core-->photons slowly work their ways outward from the core (this can take a long ass time-100,000 years)-->outer layers are dominated by convection-->He builds up in core, and H moves to a shell outside the dead core-->He ignites in the core and begins to make C
the dead remnants of the cores of main sequence stars like the Sun. Composed mostly of C and O. Surface temps can reach 200,000 K. Supported by electron degeneracy pressure
25 times fainter than on Earth
Jupiter is about 5 times farther away from the Sun than the Earth is. How bright does the Sun seem to be on Jupiter compared to on the Earth?
the 100 Watt bulb seems 10 times fainter
Imagine a 10 Watt light bulb 10 meters away from you and a 100 Watt light bulb 100 meters away. Which bulb seems fainter and by how much?
reactions that occur between the electrons of atoms. the elements themselves are left unchanged
reactions that occur in the nuclei of atoms. the original elements are changed into other elements
a type of nuclear reaction in which large nuclei split into smaller ones, releasing energy. Can happen spontaneously. Ex: natural radioactivity, atomic bombs
a type of nuclear reaction in which small nuclei fuse into larger ones, releasing energy. Requires high temperatures and densities. Ex: cores of stars, hydrogen bombs
a catastrophe in which energy would keep increasing at shorter wavelengths and that the object would emit infinite energy
(1858-1947) solved the blackbody problem by accepting that energy came in discrete amounts called "quanta." Basically, his idea was that energy is not continuous; it comes in packets (E = hv)
aka continuous spectra aka thermal spectra. A spectrum caused by electrons in dense objects randomly vibrating due to heat.
the spectrum of light released from excited atoms of an element, when atoms move down an energy level
spectra that occurs when a low-density cool gas absorbs certain wavelengths from a continuous spectrum, leaving dark absorption lines in their place,
Joseph von Fraunhofer
(1787-1826) mathematician and optician who discovered that the spectrum of the sun contains hundreds of dark lines
(1824-1887) created Kirchoff's laws:
1. Hot opaque objects produce continuous spectra
2. Hot thin gases produce emission line spectra
3. Cool thin gases between hot opaque object and the observer produce absorption line spectra
the set of lines unique to each element which always occur at the same wavelengths. Can be used to measure chemical composition, temperature, density, magnetic fields, and motion towards or away from an observer
Written by Galileo in 1610. Talked about Galileo's observations thru the telescope such as the moon's rough surface, sun spots, jupitar's moons and saturn's rings. Strongly argued Heliocentric Theory.
Pope Urban VIII
(1568-1644) an admirer or Galileo's early works and met with Galileo many times. He encourage Galileo to work on his next book, the Dialogue. However, when Galileo got in trouble for publishing that book, Urban never helped him out.
Galileo's second book, which used characters representing Galileo, followers of Aristotle, and impartial observers. Church leaders banned the book because they didn't like how one of the characters challenged God's omnipotence. Galileo had to face trial for this work.
man who invented integral calculus, developed a theory of light and optics, formulated modern dynamics, formulated the universal law of gravity, and formulated Newtons Laws
(1687) Newton's book about how the inverse square law of gravity results in Kepler's ellipses
Newton's laws of motion
1. Every body perseveres in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state."
2. F = ma
3. "For every action, there is an equal and opposite reaction"
100 times stronger
If the moon were 10 times closer, the force of gravity between the earth and the moon would be...?
16 times stronger
if the sun were 4 times more massive and twice as close, the force of gravity between earth and sun would be...?
Assistant to Brahe; used Brahe's data to prove that the earth moved in an elliptical, not circular, orbit; Wrote 3 laws of planetary motion based on mechanical relationships and accurately predicted movements of planets in a sun-centered universe; Demolished old systems of Aristotle and Ptolemy
a new planet is discovered with a semi-major axis of 4 AU. What is the period of this planet's orbit?
the model that says earth is in the middle of the universe and all other objects orbit around it in epicycles
(1473-1543) Polish astronomer who produced a workable model of the solar system with the sun in the center, or the Heliocentric model
(1543) Copernicus' book that proposed uniform circular motions and stated that all orbits are centered on the sun. Banned 73 years after publication.
problems for Copernican model
no one had observed parallax of stars, we dont feel the Earth move or rotate, it still requires epicycles to accurately match observations of the planets
(1546-1601) Danish Astronamer who produced large amounts of astromatical data but believed that other planets rotated around the sun while the sun and moon rotated around the earth
(1902-1994) philosopher who published The Logic of Scientific Discovery, and believed that science progresses only by falsifiability
what the Greeks believed
knew the earth was round, thought the earth was stationary, believed theory was more important than observation
(384-322 BCE) student of Plato who believed that there is a separation between the Earthly and Heavenly. Champion of the Geocentric model of the universe
(100-170 AD) man who refined Aristotle's geocentric system in Almagest, was able to explain the retrograde motion of the planets, and believed that planets move at constant speed in combinations of circles around earth
the process by which specific data and observations are synthesized into a more general hypothesis
according to Newton, what force keeps the Moon moving forward in its orbit around the earth?
square root of 1000 = 32 years
Saturn's orbit has a semi-major axis about 10 AU. Approximately how long does Saturn take to orbit once around the sun?
3 times smaller
If somehow the Earth's mass tripled its present value, and at the same time the semi-major axis of its orbit around the sun also tripled, how would the force of gravity between the earth and sun change?
20 years of detailed naked-eye observations of the stars and planets
what is Tycho Brahe's greatest contribution to modern astronomy?
stellar spectra differ from each other primarily because stars have different what?
main sequence star with lowest mass
Which star will fuse H into He in its core for the longest amount of time?
the earth is closer to the sun in December than it is in June
The earth orbits the Sun more slowly in June than it does in December. Keplers laws of planetary motion imply what?
cube root of 25 = 2.9 AU
The asteroid Ceres has an orbital period of about 5 years. Roughly, what is the semi-major axis of its orbit?
He was never able to observe parallax in any stars
What was a major reason that Tycho Brahe did not believe Copernicus' model of the solar system?
that Mars will change speed throughout its orbit
Which is not true of Copernicus' model of the solar system?
it would be 1/2 as large
If somehow the Earth's mass doubled its present value and at the same time, its radius also doubled, how would the force of gravity between the Earth and you (your weight) change?
he assumed stars are too far away for us to observe their parallax
The heliocentric model of the universe predicted that nearby stars would show parallax. How did Copernicus explain that no such parallax had ever been observed?
it could potentially be falsified by experiment
What did Karl Popper believe was the most important feature of a scientific theory?
23 million years ago
The Whirlpool Galaxy is about 23 million light years away from the Earth. How long ago did the light leave the galaxy?
protons must overcome the repulsion of the two positive charges
H fusion requires high pressure and temperature because:
According to Aristotle, which of these objects would fall faster (ignoring air resistance)?
it would not change
If the Earth were brought 9 times closer to the Sun, how would the luminosity of the Sun change?
1/300 the speed of light away from earth
a star is observed to have a spectral line at 602 nm. However, if the star were at rest, the same spectral line would be at 600 nm. How fast is the star moving?
5 x 10^05 cm = 500 nm
A star has a surface temperature of 5800 K. At what wavelength does it emit most of its light?
Will a thin interstellar H cloud at a temperature of 10,000 K emit a blackbody spectrum? (yes/no)
F (it would be the same)
The mass of the Sun is about 330,000 times the mass of the Earth. If the force of gravity that the Earth feels from the Sun is "F," then what force does the Sun feel from the gravitational pull of the Earth?
If the mass of the Sun magically became 4 times smaller than it is now,about how long would the Earth take to go around the sun, assuming that the distance between the Sun and the Earth stayed the same and the speed of the Earth's orbit changed by the correct amount in order to keep it in orbit?
Light from the Sun reaches earth in about 8 minutes. If Uranus's orbit has a semi-major axis of about 20 AU, about how long does sunlight take to reach Uranus?
Uranium-238 mutates to lead-206 with a half-life of 4.5 billion years. This is an example of what?
the universe is mostly electrically neutral
The electromagnetic force between a proton and an electron is about 10^39 times stronger than the gravity between them. Why then doesnt electricity control the orbits of the planets?
They must be closer to the earth than stars are
How did Galileo interpret the discovery that planets seemed to be round disks in a telescope?
z = 0.1
Suppose that you measure a spectral line (normally 600 nm) from a galaxy at 660 nm. What is the redshift, z, of the galaxy?
particles must overcome the electrical repulsion between nuclei
Why does the CNO cycle require high densities and temperatures of at least 15 million K?
100 billion years
It just so happens that if H0 = 100 km sec Mpc then the age of our universe is about 10 billion years. Suppose we find out that H0 really = 10 km sec Mpc; what would the age of our universe be in this case?
detailed analysis of thousands of stellar spectra
What did Annie Jump Cannon contribute to astronomy?
Supernova B is 5 times farther away
2 supernovae are observed in 2 different galaxies. The supernovae are identical in all ways except that from here on Earth Supernova A seems 25 times brighter than Supernova B. What can one say about the distances to the 2 supernovae?
If you measure a galaxy to have a Doppler shift of v = 400 km sec, and H0 = 100 km ssec Mpc, then how far away is this galaxy?
6 times bigger today
A galaxy is observed to have a redshift of z = 5. How does the size of the universe today compare to the size of the universe when the light originally left that galaxy?
electron degeneracy pressure
What supports a white dwarf against the inward pull of its own gravity?
Who discovered that cepheid variable stars have a relationship between their periods and their average luminosities?
16 times greater
If a stars surface temperature increases by a factor of 2 (it doubles), how would its luminosity change if everything else about the star remains the same?
Who made the first accurate determination of the size of the Milky Way galaxy using globular clusters?
What is the minimum initial mass of a star required for nuclear fission to begin in its core?
the chemical bonds that hold a person together are much stronger than the stretching of space
If the Universe is really expanding, why arent people being stretched apart by the expansion?
Crab supernova remnant and pulsar
In 1054 AD Chinese astronomers recorded the appearance of a short-lived "new star" in the modern constellation of Taurus whose location is now occupied by:
Which class of star is probably responsible for creating most of the chemical elements that make up the Earth?
not enough info to answer
Which of the following stars has the largest apparent brightness as seen from earth?
it proved CMB was coming from outside our galaxy
What was so important about the discovery of the dipole in the CMB?
For a universe with H0 = 70.4 km sec Mpc, the Hubble time would be about 14 billion years. But that is probably not the true age of our universe. Assuming they all have the same H0, which of these universes would have the youngest true age?
At what point in the history of our universe do our currently understood laws of physics break down?
What equation describes how the size and rate of expansion of the universe will change over time?