Astro5 Midterm 1

The density of ordinary matter is

4% of the crucial density

What was the approximate mass composition of the universe just before stars began to form?

75% hydrogen and 25% helium.

Calculate how much energy is released in the second step of the proton-proton chain, where ^2H ​2 ​​ H and ^1H ​1 ​​ H are fused together to make ^3He ​3 ​​ He. The masses of ^2H ​2 ​​ H, ^1H ​1 ​​ H, and ^3He ​3 ​​ He are 2.014102 u, 1.007825 u, and 3.016029 u, respectively. The unified atomic mass unit u is equal to 1.66 \times 10^{-27}1.66×10 ​−27 ​​ kg. Give you answer in Joules.

8.8×10 ​−13 ​​ Joules

Hadean (hellish) Earth (till 3.85 billion years ago):

<> crust forms, and continents just beginning to form, <> life began sometime at the end of or just after this age.

Blueshift

A Doppler shift in which spectral features are shifted to shorter wavelengths, observed when an object is moving toward the observer.

Protostar

A contracting cloud of gas and dust with enough mass to form a star

How do you know when a net force is acting on an object?

A net force must be acting whenever the object's momentum is changing.

When talking about the early stages of the universe what does inflation refer to?

A period of rapid expansion of the universe soon after the big bang.

Electron Orbital "Clouds"

As a consequence of the uncertainty principle... We don't know exact "location" of the electron, unless we disturb it with a direct measurement to 'pin it down If we try this many times, we infer a "smeared out" location in many different, possibly separate, locations simultaneously But we can calculate the probabilities of where it could be located

Gravity and Electromagnetic aren't the only two universal forces--What holds atomic nuclei together?

How can all those plus charges be held together so tightly? Must be a nuclear attractive force even stronger than electromagnetic "Strong nuclear force" only acts over extremely short distances (the size of atoms) Since this is also exerted by neutrons, they are indispensable "adhesive"

Maximum Mass of a White Dwarf

As electrons are confined to smaller and smaller regions, they must move faster and faster (uncertainty principle for waves) Chandrasekhar worked out what happens when they hit the speed of light: that is the maximum Possible degeneracy pressure Adding any additional mass to such a White Dwarf will destabilize it!

Core Collapses

At 3 Billion degrees, fission and fusion reactions, remove all of the heat that was holding up the core against the incredible gravity--> Pressure vanishes, like pulling the chair out from under a huge stack of weights--> implodes at nearly the speed of light Core mass > 1.4 Suns, too much gravity for stable white dwarf Density becomes so high that electrons can no longer exist: they bury themselves back into the protons ("Samurai electrons"): e- + p --> n + high energy neutrino So nearly all of the energy from the star escapes as neutrinos, IN A FEW SECONDS These were detected in the nearby SN 1987A!

Hydrogen, the simplest most abundant element

Atomic Number = 1 Atomic mass number = 1

Helium, second simplest first discovered by astronomers in the Sun

Atomic number = 2 Atomic mass number = 4

Solar wind particles interact with the Earth's magnetic field and atmosphere to produce

Auroras

Milky Way

Band of starlight not aligned with our Equator, nor our Solar System was revealed by Galileo's telescope to be a GALAXY of billions of Suns. That mind-boggling increase in human perspective was only the start

Meaning of Hubble's Law: Expansion

Because the universe is expanding in time and space at equal proportion, that means that at one time the universe must have been closer together and denser Since expansion speed is finite, that means if you go back in time there must be a point where all of the universe was on top of each other

Triple Alpha Reaction

Helium, the ashes of H fusion, can burn at 10 8 oK Also Need: Very High Density, to promote collisions Enough Time for 3 Helium nuclei to hit simultaneously A special "excited" state of Carbon-12 nucleus to make the reaction much more likely to proceed Rapidly, Sun's entire core is burned into Carbon, while it is a bright blue star After that no more nuclear reactions will take place in the Sun's center, only in shells of fresh Hydrogen and Helium

The particles from strong solar storms are powerful enough to destroy Earth's satellite communications, and cause other damage that could take years to recover from.

True

Thermo-nuclear fusion powers the Sun and most stars

Two protons get close enough together to stick--they manage to overcome the electric force's repulsion via Uncertainty Principle Later a third proton sticks on, making tritium Finally a fourth proton hits, to make Helium-4 Along the way, two protons are converted into positron + neutron + neutrino (thanks to weak nuclear force)

Archean Earth (3.85 - 2.5 billion years ago):

three times hotter than present-day Earth, more active plate tectonics

If no energy absorbed after being emitted from central source at r=0, then

total power received on a sphere is CONSTANT

Eclipsing binaries

two stars that block each others light --easy to measure masses of stars

Isotope

variation in neutrons

About how long after the big bang were protons and neutrons able to merge together into nuclei?

3 minutes

After first 3 minutes

Cooled to 10 million degrees Too cold for any fusion No heavier nuclei than He could form

Spectroscopic binaries

a binary which is spatially; the existence of the second star is inferred from the 2 Doppler shifts of lines: the absorption lines are DOUBLED, and continually shifting

Cutaway view

convection in the mantle pushes the plates around

Milky Way formation

Galaxy formed from giant gas cloud when it got dense enough to collapse Halo stars formed first as gravity caused cloud to contract Remaining clouds settled into flat rapidly spinning disk Stars continuously form in disks as galaxy recycles gas

Light is a radiant form of energy that travels through space in the form of fluctuating ______________.

electric and magnetic fields

ionized

electrically charged

Mantle

if you watch it over long enough times, you'd see it is actually FLOWING!

Convection Currents

in any "fluid" with a large change in temperature, including dense gas, air, or even rock (!)

Each element (atom and ion) has

its own distinctive set or pattern of energy levels.

half-life

length of time required for half of the radioactive atoms in a sample to decay

Observational Tests: Do we understand nuclear power in the Sun's Center? Test Two: Neutrinos

(Fairly) high-energy Neutrinos from H fusion reactions CAN BE DETECTED AT EARTH Oops! Only about a third of predicted neutrinos are detected! Explanation: because neutrinos have a (very tiny) little mass, they "oscillate" back and forth between 3 types, only 1 of which is detected at Earth

Birth if a star, BURST!

Gravitational collapse is often 'triggered' by an external compression Stars tend to be born together in time and space They are born with a wide variety of masses The biggest ones are always the rarest Currently our entire Milky Way galaxy forms about 1 new star per year, mostly in its gas-rich spiral arms

How much more Sun light would you expect to receive standing on Earth when compared to standing on Mars? (Mars is roughly 1.5 AU from the Sun)

2.25x

Universe Timeline

0-3 Minutes the universe's center was so hot and high speed that nothing could stick together/fuse Violent, high-energy collisions

The Two Revolutionary Ideas of Quantum Mechanics

1) Electromagnetic radiation has properties of waves, but also of massless particles, called photons, with: Energy of a photon = Constant x Frequency 2) ALL (Massive) particles also have wavelike properties, so they must also obey the wave Uncertainty Principle (ex: they do not have precise locations, only probability distributions) (3) (At a deeper subatomic level, quantum principles apply to the structure of SPACE ITSELF)

What forces act on matter?

1) Gravity is universal attractive force between all masses 2) Electromagnetic force operates on charged particles, holds atoms and molecules together Both have "infinite" range, strength dropping as square of the separation Gravity is vastly weaker, but can never be cancelled out, so dominates on large scales

Shortcomings of the Big Bang Model

1. Why is the large-scale Universe so smooth (nearly same temperature in opposite directions)? [the horizon problem] Where does structure come from (those small density inhomogeneities we see in Cosmic Microwave Background)? [the structure problem] 3. Why is the density of matter so close to critical? (in early stages, density had to be within one part in a trillion of critical density for us to be here today!) [the "flatness" problem]

Sun will burn for

10^10 years

Universe Age

13.5 Billion years

MASS DETERMINES STELLAR EVOLUTION

A star's location on the main sequence is determined by its mass: higher mass stars burn hotter in their cores, generating more power, but for a much shorter lifetime The Main Sequence is a Mass Sequence If our nuclear power theories are correct, this should also correspond to a lifetime sequence

excited state

A state in which an atom has a higher potential energy than it has in its ground state

Pangea

A supercontinent containing all of Earth's land that existed about 225 million years ago.

Assume that 10% of the Sun's mass comprises of hydrogen in the core, where the temperature is high enough for them to be converted to helium via the proton-proton chain. Calculate how much energy is released in total in this process. Recall that the proton-proton chain has an efficiency of 0.71%, and give your answer in units of Joules.

About 1.3 \times 10^{44}1.3×10 ​44 ​​ Joules

Based on your answer to the previous question, for approximately how long can the Sun shine via the proton-proton chain? Recall that the Sun's luminosity is the rate at which it emits energy released via the proton-proton chain.

About 10^{10}10 ​10 ​​ years

Planetary Orbits

Accelerated trajectories caused by the force of Gravity, but it comes from the combined force of Large spherical masses (like the Sun) Three results from Newton's (and Liebnitz's) calculus: 1) adding up all parts of a sphere produces the same gravitational pull as if all its mass were concentrated right at its center 2) Escape velocity is Sqrt(2) = 1.414 times larger than orbital velocity: Vescape = (2 G M / R)1/2 3) if V<Vescape, orbit is ellipse; for V=Vescape it's parabola; for V>Vescape it's hyperbola, the 3 conic sections

Convection plus Earth's Rotation

Air Movement along a meridian (N-S) is affected, like trying to walk straight on rotating platform of a carousel experience a sideways Coriolis Force, Upper Winds blowing north from the Equator (warmed air rises) veer rightward as they move closer to the Earth's axis at the North Pole; surface winds do opposite This pattern caused by solar heating plus Earth rotation produces all the global trade wind (and weather) patterns -------------------------------------- End of Crash Course on Meteorology. Next up... Geology--

Angular Momentum: a new Conserved quantity

All rotating objects have angular momentum (spin speed and direction and size of circle) L = mvr ; (a vector perpendicular to the plane of rotation) Examples: helicopter rotor, ice skater, spinning top Gyroscope (to stabilize spacecrafts) is a spinning wheel whose axis maintains its direction; slow precession like the Earth's axis along the Circle of Precession

Forces at the beginning of the universe

All the same/identical force, separated later

How does an absorption spectrum differ from an emission spectrum?

An absorption spectrum shows as a pattern of dark lines against a continuous spectrum whereas an emission spectrum is a pattern of bright lines against a dark background.

Newton's First Law:

An object at rest will remain at rest, and an object moving in a straight line at constant speed (= constant velocity) will not change its motion, unless an external force acts on it. Greeks were wrong about "natural state of motion", since they neglected friction. (We only know of 4 fundamental forces in the world, and these are thought to be different aspects of one single superforce).

Halo, disk, and bulge of mily way

Anatomy of galaxy

Radiometric dating

Careful measurement of the proportions of various atoms and isotopes in the rock. Reminder: Each chemical element is uniquely determined by the number of protons in its nucleus. Different isotopes of the same element differ in their number of neutrons.

Humans can see the difference in certain wavelengths of light in the form of...

Color

Increasing sideways velocity given to a projectile: Object in orbit

Continuous fall

Through what process is the heat generated at the Sun's core transferred to the outer layers of the Sun?

Convection

Big Bang agrees with

Cosmic Microwave primordial levels of Helium/abundance in the universe

Birth of a star

Densest clouds of gas in a galaxy cool off (by radiating visible and IR photons) When they become cold, gravity wins over gas pressure --> runaway gravitational collapse Instability: Positive Feedback: when gravity contracts a lump of mass, the results is that all pieces become closer together --> amplifying the gravitational force causing the contraction --> further accelerating the gravitational collapse --> unstable runaway process, until a new non-gravitational force builds up enough strength to balance the inward gravity

HEAVY HYDROGEN IS..

Deuterium 3rd most abundant element Isotope of Hydrogen Atomic numer = 1 Atomic mass number = 2

What to study for midterm

Distinguish between speed, velocity, and acceleration. Speed is the rate at which an object is moving. Velocity is speed in a certain direction. Acceleration is a change in velocity, meaning a change in either speed or direction.

Light is emitted from an atom in the form of photons when...

Electrons fall to a lower energy level.

What occurred about 380,000 years after the big bang?

Electrons merged with nuclei to form atoms.

The Universal Law of Gravitation

Every mass attracts every other mass through the force called gravity The force of attraction is directly proportional to the product of their masses The force of attraction is inversely proportional to the distance between the objects Fg = G x M1x M2 / d2 The gravitational force exerted by a large object is proportional to the product of the masses. This guarantees that Newton's Third Law is always satisfied by gravity.

Orbital Paths

Extending Kepler's Law #1, Newton found that ellipses were not the only orbital paths. possible orbital paths ellipse (negative energy: bound) Parabola (zero energy: unbound, barely) hyperbola (positive energy: unbound)

If the Sun were to suddenly produce Helium at its core at a decreased rate, observers on Earth would would perceive the dimming of the Sun after a delay of 8 minutes and 20 seconds (the time that it takes light to travel to Earth from the Sun)

False

How fast do continents/plates move?

Few inches/year

Earth factors

From g=GME/R2, Mass Average density= 5.5 times water! [higher than surface rocks, 3x water] Earth originally molten throughout, and then cooled ... it's still cooling today It underwent differentiation early on, like all large solar system bodies ... Denser materials (iron, nickel) sank to the center, while lighter materials stayed on top (mantle made of "silicates"). Furthermore, the dense metals and the silicates are  imiscible fluids, like oil and water.

What extremely powerful physical process generates the energy that powers the Sun at its core?

Fusion

Confirmation of Olber's Paradox

Hubble discovery shows Doppler shifts of galaxies in 20th century The redshift recession velocity is DIRECTLY PROPORTIONAL to the DISTANCE of each galaxy: V = HD H is Hubble's Constant

Galaxies started as...

Huge clouds of gas Huge dense clouds collapse to form stars

Kirchhoff's 3 Laws of Thermodynamics--

I. A hot, low density gas emits light of only certain wavelengths - atomic collisions "excite" the electrons to higher energy orbits. After less than a millionth of a second, they tend to drop back down to lower energies, emitting a distinctive: emission line spectrum. II. A hot, opaque glowing object (solid or gas) emits a continuous (rainbow) spectrum, because these emission lines have all gotten smeared into one continuous blend. Opaque Surfaces Emit Universal "Blackbody" Radiation Spectrum III. When light having a continuous spectrum passes through a cool gas, dark lines appear in the continuous spectrum, because only photons having exactly the right energies can be absorbed by electrons as they jump up to higher energy orbits (excitation by photon absorption), imprinting a distinctive: absorption line spectrum

Olber's Paradox

If the universe has infinite time and space, there would be an infinite number of stationary stars, making the night sky bright (but the brightness is not infinite), which is not the case

Newton's Second law:

If velocity is changing, that is an acceleration, which means a force is exerted on the object. Its acceleration is inversely proportional to its mass: a = F/m Mass resists changes in velocity: it is inertia

Conservation of Angular Momentum

In the absence of a net torque, the total angular momentum of a system remains constant.

The largest element that can be formed via fusion in stars is

Iron

How does the acceleration of gravity depend on the mass of a falling object?

It does not. All falling objects fall with the same acceleration (on a particular planet).

Plate Tectonics: Movement and Activity

Lithosphere is divided into 16 plates with oceans and continents Summary of results of continental (plate tectonics) drifts: Rift Zones: Plates pulling apart along a ridge, which may show volcanic activity, e.g. mid-Atlantic ridge, Subduction Zones: Plates colliding one plate forces under the other (e.g. oceanic Japan trench, "Ring-of-Fire" volcanoes along the Pacific Rim), or rising to form mountains (e.g. Himalayas) Fault Zones: Crustal plates sliding along each other - plate boundaries are called "faults" (e.g. San Andreas)

Hydrogen fusion: several steps transform 4 protons Into a single Helium-4 nucleus

MASS IN: 4 protons = 4 x 1.008 = 4.032 atomic mass units MASS OUT: 1 He-4 = 4.002 atomic mass units What's the difference? 0.03 out of 4 amu's ¾ of a percent of the total mass has been CONVERTED into Pure Energy

Earth as a planet: basic properties are well worked outGOAL: know what is typical, what is special (for habitability)

Mass (density): 5.5 times water! [higher than surface rocks, 3x water] What is interior structure, and how is that related to continental drift and magnetic field? How old is it? What is the role of its atmosphere and how has that changed? Cause of tradewind patterns: solar heating plus Coriolis force (now you know meteorology!) Seasons: why don't they "run away"? ...later!

Masses of Stars

Mass is the single most important property of any star. at each stage of a star's life, mass determines... what its luminosity will be what its size, and therefore its surface temperature will be The mass of a star can only be measured directly by ... observing the effect which gravity from another object has on the star This is most easily done for two stars which orbit one another...a binary star!

Magnetic and Rotation Axesare not perfectly aligned

Motions in our Molten iron core Produce currents, Which make Magnetic fields

Newton's Triumph: Apply his Gravitational Force to EXPLAIN ORBITS, Supports Kepler's Laws

Newton found that Kepler's first two laws apply not only to planets, but to any object going around another one under the force of gravity (or any inverse-square law force) The orbits do not have to be elliptical With higher energy (velocity), they can also be parabolic or hyperbolic, the 3 kinds of Conic Sections

Iron Crisis

No Nuclear Reaction can extract energy from Fe-56 Fusing it CONSUMES energy Fissioning it CONSUMES energy Core continues getting crushed, reaches 3 Billion degrees Iron undergoes fission and fusion reactions (producing the heaviest elements) All these reactions remove all of the heat that was holding up the core against the incredible gravity

Why does fusion occur in the Sun's core ?

Nuclear fusion a reaction where heavier nuclei are created by combining (fusing) lighter nuclei. all nuclei are positively charged Electromagnetic force causes nuclei to repel each other. for fusion to occur, nuclei must be moving fast enough to overcome E-M repulsion this requires high temperatures & pressures (>10 Million C) When nuclei get close the strong nuclear force takes over, binding them together: Eddington realized uncertainty principle was needed to let this happen

+1 Second Universe Timeline

Nuclear fusion begins to take place throughout universe to form deuterium first, a few minutes later it stabilizes to make helium-4 nuclei

Model predicts a 3-to-1 H:He mass ratio

OBSERVED: Minimum 25% He in each galaxy

Coriolis Force

Object moving north from the equator moves eastward (right) due to An eastward velocity which gets higher relative to the Earth's surface as it moves northward Gets closer to the Earth's axis; therefore the rotational speed increases, like that of an ice skater pulling arms inward

Newton's 3rd Law applied to orbits

Objects actually orbit around their common center of mass, because the gravitational force accelerating each one is the same, so that small object must accelerate more (swing around on a wider orbital path). If one object is more massive than the other, the center of mass is closer to the more massive object For objects equal in mass, the center of mass is halfway between the two.

"Heavy" Elements Accumulated in the Milky Way Over Time from Supernovae

Oldest star clusters are composed of ALMOST primordial gas: 90% H and 10% He After several billion years, much of the Universe had accumulated 0.1 % heavy elements (as in our Sun), due to generations of star birth and supernova death This gradual build-up of heavy elements continues today in galaxies, but very slowly

Solar Energy Generation is Stable for most of its life

Only subtle change: core gets denser as it gradually turns into Helium Temperature adjusts upward. Nuclear fusion runs faster at this higher temperature. Sun is now 30% brighter.

Earth's atmosphere has changed a lot!

Originally it was (poisonous) methane, from outgassing Condensation of water forms oceans early in the history of Earth, which were cool enough to survive Carbon dioxide dissolved in water or chemically bound, e.g., carbonate rocks 72% molecular nitrogen N2 1% water H2O Traces of argon, 400+ppm CO2, ... molecular oxygen O2 was originally 0%, today 21% Why? Photosynthesis in oceans: CO2 organic materials + O2 Ozone O3 layer This allowed O-breathing animals, and colonization of land by plants and then animals

Cosmic Microwave Background

Penzias + Wilson (1967) prove Big Bang/beginning by accidentally detecting radio waves of photons which became transparent during the Big Bang

The 4 Forces and where they operate

Planets, stars and galaxies are held together by the Gravitational Force. Gravity completely dominates all motions on large scales. Atoms are held together by the Electromagnetic Force, since opposites attract. This force also drops as 1/distance2, but unlike gravity, likes repel. Each nucleus is made up of protons and neutrons and is (fortunately) held together by the Strong Nuclear Force. Nuclear forces only act over a very short range, comparable in size to the nucleus of an atom Electrons are can be converted to other particles - photons, and neutrinos - through the operation of a force called the Weak Nuclear Force.

Brightness/intensity =

Power (per unit area)

Where Does Structure Come from?

Quantum Mechanics: on smallest scales, total amount of mass is inherently UNCERTAIN, and must have fluctuations from one point to another. These quantum ripples would be greatly magnified by inflation. After inflation, the quantum fluctuations have become huge, all the way up to the size of the observable Universe

How is Nuclear Energy Transported Out of Sun's Center?

Radiation Zone energy travels as photons of light, which continually collide with particles always changing direction (random walk), photons can change wavelengths, gradually shifting from gamma rays down to visual photons this is called radiative diffusion (1) This is a slow process! It takes about 1 million years for energy to travel from the core to the surface. So fusion reactions COULD have shut down in Sun's center for last hundreds of thousands of years!--> We need a test of fusion happening NOW

What type of light on the electromagnetic spectrum has the longest wavelength?

Radio Waves

How can we determine the surface composition of the Sun and other stars without actually visiting and/or attaining a sample?

Spectral lines from the these objects provide a unique barcode that allows us to analyze the content of these distant objects.

What Happens when Much More Massive Stars Exhaust Hydrogen in their Centers

Stronger gravity makes their cores much hotter after triple alpha burning Carbon nuclei "burn" (fuses) to Oxygen Then Oxygen burns to Neon, which later burns to Magnesium, and to Silicon Massive star's core exhausts one fuel, gets hotter, then can ignite its ashes as its next fuel Massive star develops an onion-layered interior

Basic Properties of the Sun: a completely ordinary star

Surface Temp = 6000 C Distance: 1.5 x 108 km = 1 A.U. Mass: 2 x 1030 kg Radius: 7 x 105 km Average Density: 1.4 g/cm3 Luminosity: 4 x 1026 watts

What ends the first Red Giant phase?

The He core contracts until it heats to 108 K He fusion begins ( He C) called the "triple- process" All He in core rapidly converted into 12-C With that 2nd (and final) fuel supply exhausted, core shrinks again Sun has its second and final red giant phase (double shell-burning star) Extreme luminosity and instability EJECTS OUTER LAYERS OF STAR'S ATMOSPHERE, leaving behind hot core

Rock of Ages

The Solar System is 4.57 billion years old. How do we know this? Atoms are identical: young atoms are indistinguishable from old atoms Some (heavy) Atomic nuclei can undergo spontaneous radioactive decay and turn into other elements or isotopes (more later...)

What Keeps the Sun Stable?

The Sun began as a cloud of gas undergoing gravitational collapse. the same heating process, once proposed to power the Sun, did cause the core of the Sun to get hot & dense enough to start nuclear fusion reactions Once begun, the fusion reactions generated energy which provided an outward pressure. This pressure perfectly balances the inward force of gravity: deeper regions, with more mass weighing down, must be hotter This balance is called gravitational (hydrostatic) equilibrium. Central temperature must be 15 Million C (worked out by Eddington

Seismology "Observes" the Solar Interior

The Sun's interior is opaque... we can not see directly into it with light We can construct mathematical computer models of it. the models are a grid of temperature, pressure, & density vs. depth these values are calculated using known laws of physics Test One: We can directly measure sound waves moving through the interior we observe "sunquakes" in the photosphere by using Doppler shifts speed of sound waves can be checked against interior conditions predicted by models: which turn out pretty accurate! There is another way to see directly into the core...neutrinos!

What is the acceleration of gravity?

The acceleration of an object falling to the ground because of gravity. On Earth's surface, it is 9.8 m/s2

In the equation E\propto \frac{1}{\lambda}E∝ ​λ ​ ​1 ​​ , what does E refer to?

The energy of an individual photon of light.

The Sun's Energy Source

The first theories invoked chemical reactions or gravitational collapse. chemical burning (eg huge ball of coal?) would run out in 100 million years conversion of gravitational potential energy into heat as the Sun contracts would only keep the Sun shining for 25 million years 19th-century radioactive dating indicated the Earth was older than that Development of nuclear physics led to the correct answer the Sun generates energy via nuclear fusion reactions Hydrogen is converted into Helium in the Sun's core the mass lost in this conversion is transformed into (an enormous quantity of) energy The total mass plus energy is conserved in all reactions

Expansion of the universe

The galaxies are not moving; the space between them is getting larger Space is UNIVERSALLY EXPANDING without a center

Newton's Laws (gravitational motion)

The gravitational pull of the Sun keeps the planets moving in their orbits. Without this central force, they would fly off on straight tangents. A = v2 /r

How did the horizon of the visible universe in the early universe compare to that which we have today?

The horizon was smaller and got larger as time went on.

Stellar Evolution

The life of any star can be described as a battle between two forces: Gravity vs. Pressure Gravity always wants to collapse the star. Pressure holds up the star. the type of star is defined by what provides the pressure Remember Newton's Law of Gravity the amount of gravitational force depends on the mass gravitational potential energy is turned into heat as a star collapses A star's life and death will be determined by its mass

Mid-Atlantic ridge steadily forming new (magnetic) rock on its floor

The new crust created at rift zones preserves the magnetic field present at the time it solidified; from this we can tell that field reversals occur about every 500,000 years:

How do we determine the type of an atom? (hydrogen, helium, gold, etc.)

The number of protons in an atom

Why is mass converted to energy in a fusion reaction?

The protons and neutrons in a helium nucleus are held together more tightly than in a hydrogen nucleus.

What is the name of the force that holds the nucleus of an atom together?

The strong nuclear force

What is surprising about the universe from the period observed using the cosmic microwave background?

The universe was smoother than expected.

How do stars evolve when their cores exhaust all their Hydrogen?

To maintain pressure balance, Gravity condenses and heats their core (By energy conservation), their surface expands Interior heats up, while surface cools down H fusion can now occur powerfully in a shell around the (hot, dead) He core This "shell-burning star" has become a red giant

Different isotopes of the same kind of atom vary in...

Their number of neutrons

Some exotic particles don't feel the strong nuclear force

Their only interactions are from gravity and the "weak nuclear force" Typical example is one kind of radioactive decay where neutron switches into a proton plus an electron (plus a "neutrino") (That's why weakly interacting particles are so hard to detect—it would take a lead shield a few light years thick to stop most neutrinos). They may account for most of the mass in the Universe (!!) Similar weak nuclear reactions make supernovae explode These Weakly Interacting Massive Particles are probably 90% of the entire Mass of the Universe

How might fundamental forces (gravity, the weak force, the strong force) be affected by extremely high temperatures?

They become the same force.

What property of electrons results from the fact that they exist as waves?

They can only exist at very specific energy levels in an atom.

Evolution of cores of Supergiant Stars

They have enough gravitational energy to heat up to 6 x 108 K. C fuses into O C is exhausted, core collapses until O fuses. The cycle repeats itself. O Ne Mg Si Fe

Difference between nuclear fusion and fission

This occurs spontaneously in heaviest (radioactive) nuclei In this process neutrons and He nuclei fly out, triggering more fissions possible chain reaction (if you have high enough purity of n-producing fuel)

What is thought to be the cause of temperature variations in the cosmic microwave background?

Tiny quantum fluctuations in the early universe expanded to a macroscopic size by inflation.

Implications of Olber's Paradox

Universe and its contents must have evolved from a smoother simpler state to a current complex one

Earth's Interior revealed by earthquake wave transmissions (seismology)

Unlike Pressure Waves, Transverse (Shear) waves cannot travel through liquid: Liquid (iron) Core leaves an earthquake wave shadow of S waves

Most of the light emitted by the Sun comes in the form of...

Visible light

Solution to Olber's Paradox

We cannot receive photons from infinitely far away DUE TO THE FACT there has only been a FINITE time for them to travel BECAUSE the universe has not been producing stars for an infinite time in the past THEREFORE, there must have been a START to the universe, aka no infinite time in positive and negative directions!

Galileo's experiment revisited

What is your weight and mass ? Weight W is the force of gravity acting on a mass m causing acceleration g Using F = m a, and the Law of Gravitation W = m g = G (m MEarth) /R2 (R - Radius of the Earth) The mass m of the falling object cancels out and does not matter; therefore all objects fall at the same rate or acceleration g = GM / R2 = 7 x 10-11 x 6 x 1024 / (6000 x 1000) 2 i.e. constant acceleration due to gravity 9.8 m/sec2

to know for Midterm

What process creates energy in the Sun? Fusion of hydrogen into helium in the Sun's core generates the Sun's energy. Why does the Sun's size remain stable? The Sun's size remains stable because it is in gravitational equilibrium—the outward pressure of hot gas balances the inward force of gravity at every point within the Sun. How long will fuel supply last, in various kinds of stars? What happens next?

Have you ever been weightless? Have you ever been massless?

You are weightless every time you jump, because you are in free-fall while in the air. You have never been massless, because mass is a basic property of the matter in your body.

Several shortcomings of the Big Bang Theory can be answered if it began with a brief spectacular episode of INFLATION:

What? In only 10-36 second, the energy released by the "phase transition" of the vacuum caused a sudden and dramatic expansion of the size of the Universe, by a factor of perhaps 10100 times. Results: 1. All particles were produced out of the "false" vacuum [the Ultimate Free Lunch, during inflation it does not violate conservation of mass/energy!] 2. "Constants of nature" are set during this inflation, and could have been different! Reading from "Just Six Numbers": We live in a Universe that is remarkably tuned for life. Is this the "Anthropic Principle", or something deeper? 3. Inhomogeneities were born, producing huge structures

Newton's third law

When object A exerts a force on object B, object B exerts an equal and opposite force on object A. Don't forget these forces are on different objects, so they do NOT cancel out! Ex: space fight. (This is just another way of saying that total momentum is conserved.) This explains how we get around, on Earth or in space: we always need something to push us, friction helps us push on it. Ex: how to escape from an ice-skating rink Mathematical description of laws of motion and conservation were a 50-year leap forward. But then Newton was ready for ANOTHER one...

Newton's third law:

When object A exerts a force on object B, object B exerts an equal and opposite force on object A. Don't forget these forces are on different objects, so they do NOT cancel out! Ex: space fight. (This is just another way of saying that total momentum is conserved.) Watching an object accelerated by gravity tells us the force being exerted by a companion EVEN IF IT'S INVISIBLE

Planetary Nebulae

When the Red Giant exhausts its He fuel the C core shrinks Low & intermediate-mass stars don't have enough gravitational energy to heat to 6 x 108 K (temperature where Carbon fuses) The He & H burning shells overcome gravity the outer envelope of the star is gently blown away this forms a planetary nebula

Centripetal Acceleration

While the ball is on the string the velocity changes continuously to keep the distance to the hand constant. The speed of the ball remains constant, only the direction changes. This is called centripetal acceleration. When the string breaks, the central force is no longer being applied to the ball so it no longer undergoes centripetal acceleration. When this happens both the speed and the velocity become constant and the ball goes in a straight line.

Dark Energy

a mysterious force that appears to be causing the expansion of the universe to accelerate

The precise pattern of wavelengths in an absorption or emission spectrum is ___________.

a signature of the types of atoms in the object.

binary star system

a star system that contains two stars

inflation (of the universe)

a sudden and dramatic expansion of the universe thought to have occurred at the end of the GUT era

red giant

a very large star of high luminosity and low surface temperature. Red giants are thought to be in a late stage of evolution when no hydrogen remains in the core to fuel nuclear fusion.

Geological eras of Earth's history

assembled by sequencing the strata worldwide: - sedimentary rocks are laid down in a horizontal manner - younger rocks are placed on top of older rocks - fossils played a key role in identifying layers at different places

Electrons move in

cloud

Convection

common to terrestrial planets, gas giant planets, the Sun, all stars convection is a mechanism for transporting heat upwards Planets have left-over heat, plus radioactive decays it is the rising and falling of a "fluids" in convection cells hot fluid expands and rises. At the top of the cell, it cools, contracts and sinks this sets up a circulatory pattern

Ground state

electrons in the lowest available energy level

I (4 r2) = Constant

energy conservation

Potential Energy of Matter Itself

energy is stored in matter itself this mass-energy is what would be released if an amount of mass, m, is converted into energy E = mc2

Majority of the mass in the universe is

extraordinary, such as WIMPS

Wave formula

flamda=c f = frequency lamda = wavelength c = speed of light

Earth's magnetic field protects

from high energy solar particles

'g' on the Moon

g(Moon) = a = G M(Moon) / R(Moon)2 G = 6.7 x 10-11 newton-meter2/kg2 M(Moon) = 7.3 x 1022 Kg R(Moon) = 1700 Km (Or shortcut: scale to Earth: M drops by 100; R drops by 4: 16/100 = 1/6th of Earth surf gravity) g (Moon) = 1.6 m/sec/sec About 1/6 of g(Earth); all falling objects on Moon take exaggerated slow arcs compared with what we're used to here, astronauts hop along as if they were hanging from strong springs

Ion

gain or loss in one electron, making the atom charged

What type of photon on the electromagnetic spectrum has the highest energy?

gamma rays

Radioactive isotope

has a nucleus prone to spontaneous change or decay; breaking apart, or having one of its neutrons turn into a proton (plus electron), changing one element into another one

two or more atoms combine to form a particle (by "sharing" their outer electrons)?

molecule

Most of an atom's mass is contained in the...

nucleus

In the Era of Nucleosynthesis, i.e. the first three minutes

number of protons & neutrons roughly equal as long as T > 1011 K below 1011 K, proton-to-neutron reactions no longer occur Free neutrons still decay into protons, half-life is 11 minutes protons begin to outnumber neutrons At T < 1010 K, the products of fusion reactions no longer break up. Helium, Deuterium, & Lithium remain stable At this time, Big Bang model predicts a 7-to-1 proton:neutron ratio.

When you confine a wave,

only certain wavelengths/frequencies are allowed

uncertainty principle

the idea put forth by Werner Heisenberg in 1927 that the behavior of subatomic particles is uncertain, suggesting that all of the physical laws governing the universe are based on uncertainty

What's the Matter at t<1 second?

pairs of matter and anti-matter

Geological eras of Earth's history

sedimentary rocks are laid down in a horizontal manner - younger rocks are placed on top of older rocks - fossils played a key role in identifying layers at different places

spectroscopic binaries

separation between stars is small so that the orbital velocity is high; binary nature was detected through Doppler shift in spectra of the stars

Redshift

shift of light to a longer wavelength as it moves away

proton-proton chain

the chain of reactions by which low-mass stars (including the Sun) fuse hydrogen into helium