astro final
What determines the atomic number of an atom? What determines the atomic mass number? Where are the electrons in atoms, and what force keeps them there?
- # of protons in nucleus -The number of protons plus the number of neutrons. -electrons occupy orbitals; electromagnetic force -The electrons are "smeared out" in a cloud around the nucleus and are kept there by the electromagnetic force
What is the role of galaxy mergers according to recent ideas, and why do some astronomers use the term galaxy assembly? What evidence is there that applies to our own Galaxy?
-"Major Mergers": 2 ~equal sized galaxies merge -"Minor Mergers": when big galaxy eats little galaxy -Galaxy Assembly: large galaxies grow by 1) mergers w/ other galaxies (major mergers), 2) accretion of smaller galaxies (minor mergers), and 3) inflows of gas which is the "material" to make new stars -evidence: MW's "Field of Streams"
Approximately how long does it take photons produced in the Sun's core to travel from the core to the surface; to travel from the surface of the sun to the surface of the Earth? (Know the values closely enough to be able to recognize the right answer)
-100,000 years -8 minutes
What phenomenon was detected for the first time from the bright, nearby supernova in the Large Magellanic Cloud seen in 1987A, and what idea did it confirm?
-1st observed supernova -confirmed radioactive source of energy for visible light emissions -Neutrinos arrived before light: escaped before light did, total energy in neutrinos represented ~99% of energy of explosion
How was matter in general (dark and ordinary) distributed in the universe at the time of recombination (CMB)? How is the matter distributed in the universe today?
-@ time of recombination things = evenly distributed -but the universe has grown lumpier with time.
Explain the basic process of neutron-capture reactions and how they differ from the fusion reactions that produce elements lighter than Fe
-A neutron is captured by the Fe nucleus, if nucleus is unstable then one of the neutrons is turned into a proton plus an electron which converts the element into the next higher chemical element. -Must have a metal nuclei present, supply for free neutrons needed
What kinds of substances/objects produce each of the three types of spectra classified by Kirchoff? Which of these enable determination of which elements they're made of? Are there any types of spectra from which you cannot tell which elements are present?
-A solid or dense hot gas emits a smooth or so called "continuous" spectrum, with a shape and height set by its temp -A hot low density gas emits lights at a few wavelengths depending on what elements are present. They produce bright narrow emission lines. -Cool low density gas absorbs at only a few wavelengths producing dark narrow gaps (absorption lines) -emission and absorption lines -blackbody spectrum
Why does an object approaching the event horizon of a black hole feel a tidal force, and what unusual effects start to become apparent in this region of extremely strong gravity?
-A tidal force is strong when the local strength of gravity is changing rapidly with distance, as near as an event horizon. -Object is stretched up/down and compressed inward = spaghettification
What are planetesimals, and how do they develop in the disk around a star that is forming?
-As one star from binary system gains mass from the other, forms an accretion disk filled with dust grains -These dust grains collide from accretion, creating bigger objects Dust → pebbles → planetesimals → planets -As objects grow larger, change from one to another is when gravity overcomes object and allows it to grow -Rolling stone gathering moss -Collisions of particles cancels out solids upward/downward inward/outward motion, creating circular orbit
How do astronomers explain the existence of pulsars with periods of a few milliseconds?
-Believed to be recycled/rejuvenated pulsars. They were once normal pulsars born in a supernova that lost rotational energy through radiation, slowed down ,and faded as radio sources. -However, if it's in a binary system, then the mass transferred from the other star has angular momentum from the orbital motion that will speed up the rotation of the neutron star when it lands.
Explain why the composition of the interstellar medium (ISM) is changing over time, in particular the fact that the concentration of elements heavier than H and He keeps increasing.
-Changing because formation of stars/galaxies and lives of them are creating new materials/elements -As more stars form, more material heavier than H/He is created
What was the role of dark matter in forming the first stars and galaxies?
-DM collected into halos of a million-billion M. -Smaller halos formed first; their gravity later drew in gas which contracted to form the first stars and galaxies
Roughly how much dark matter is present in the universe, compared to the amount of ordinary matter? Is dark matter the dominant (Biggest) constituent of the universe?
-Dark matter is the dominant source of gravity by a factor of 6, outweighing ordinary matter -DM = 23% of universe; the great majority of mass -BUT dark energy = 72%; dominant constituent of uni. and causes exp of uni to accelerate
What kind of event caused the first direct detection of gravitational waves by LIGO? What kind of event detected by LIGO also produced electromagnetic radiation?
-Detected waves of wavelength roughly equal to distance between detectors -Exact signal expected of two merging BHs of mass 30M -proved large BHs exist and merge -As they get closer, orbit faster, shorter periods, increase frequency (rising pitch in sound) -Amplitude grows from more energy in gravitational waves -Merger of two neutron stars saw the production of electromagnetic radiation
Name the particles other than deuterium that result from the first step of the P-P chain of nuclear reactions. What happens to each of these particles after they are created?
-Deuterium, Neutron, neutrino and a positron -D remains, neutrino escapes, and positron is destroyed almost immediately
How did the heating of the early Earth lead to its present, multi-layer structure (Fe/Ni core, rocky mantle) How is the presence of a molten Fe core helpful to life on Earth?
-Earth was bombarded by Mars-sized bodies while it was forming mixed with radioactive decaying caused the Earth to heat up, Fe/Ni sank to the center and Earth reformed as a molten body with a moon -The molten Fe core generates a magnetic field that protects Earth from harmful solar particles to this today
What are the requirements for an interstellar cloud to start collapsing? How do the properties of molecular clouds meet these requirements?
-Forces of cloud can no longer support gravitational force and succumb to gravity -Gravitational potential energy is converted to kinetic energy, etc, etc -Molecular clouds are dense, dark and cold; they have little pressure/kinetic energy so easily overcome by gravity -Jeans Mass
Why do the surfaces of some AGB stars show that there are large amounts of carbon present?
-He shell flares up in brief runaways, after each pulse convection carries C to star's surface -these episodes repeat inc amount of C brought to surface -referred to as "dredge up"
What elements and isotopes were made by nuclear reactions in the first few minutes after The Big Bang? For each of these, was a lot or just a small amount produced?
-He; a lot -D and Li; a little
How does the spectrum of a cooler thermal emitter ("blackbody") compare with that of a hotter one? Note: There are two significant aspects; describe both
-Hotter objects emit bluer photons at the spectral peak -Hotter objects emit more total radiation per unit surface area
What particles/nuclei are the starting point of the pp-chain of nuclear reactions, and what comes out when the sequence is completed? What are these for the CNO-cycle reaction?
-IN= 4 protons OUT=He Nucleus, 2 gamma rays, 2 positrons, 2 neutrinos, protons -Proton turns into neutron, yielding deuterium, neutrino, and positron -D remains, neutrino escapes, and positron is destroyed immediately -CNO: 4 H atoms to HE on carbon nucleus acting as a catalyst
In which region of the Sun (range in radius) is energy transported mainly by photons? In which region does convection carry the energy? In which region does fusion occur?
-In most of the volume of our sun energy passes through local material in the form of photons or light. Energy is brought from the center to the surface this way -convection on surface -fusion in the core
What do the terms isotope, ion, and molecule mean? Give examples of each.
-Isotope: each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties. (Carbon 13) -ion: an atom or molecule with a net charge due to the loss or gain of one or more electrons (He+1) -molecule: two or more atoms share their electrons but have separate nuclei (H20)
What do astronomers think triggered an era of heavy bombardment of the inner Solar System (including the Earth) early in its history?
-Jupiter and Saturn fell into resonant orbits (locked to each other), causing Neptune and Uranus to switch places, flinging asteroids
What are the axes of the Hertzsprung- Russell Diagram, and in which directions do the values increase? Which regions in the diagram contain lots of stars (name three regions)?
-Luminosity (Increases bottom to top) Surface Temperature (Increases from right to the left) -Majority of stars fall along the diagonal track called the "Main Sequence" -Other regions are Giant branch (Top right), horizontal branch
What is the significance of the Main Sequence? For any two stars in different places along the Main Sequence, what properties do they have in common, and what properties differ?
-MS = main lifetime of star - in common: fuse H to He in core - differ: mass, lifetimes, temp, luminosity -MS is a MASS SEQUENCE: each point occupied by stars of specific initial mass - relationship b/w mass & luminosity only on MS (more mass = more luminosity) -Mass luminosity principles --> mass lifetime principles: larger luminosity, shorter lifetime
How were pulsars discovered (what was observed)? Why did astronomers conclude that these sources must be neutron stars?
-Using a radio telescope, Jocelyn Bell noticed regular pulses of radio emission. -Because they found remnants of supernovas
Name and describe the fusion reactions that occur in lower-mass stars (less than 8M) from the MS to the ends of their lives. For each reaction, state the fuel (input) and product (Output)
-MS: H --> He; when done, area above core begins burning H -1st time RG: H burning shell, shrinking core -horizontal branch: ("2ndMS") He fusion in core; "triple alpha process" He --> C, O -2nd RG: "double shell burning" He fusion in shell above core, H fusing in shell above that, degenerate C/O core -star becomes: cooler, larger, more luminous
Describe the sequence of life stages for high-mass stars (greater than 8M), in terms of their interior structure, fusion reactions, and positions (or track) in the HR diagram
-MS: H fusion in core -Red Supergiant: H fusion in shell -Blue SG: He fusion in core -goes back and forth to red & blue positions on diagram as more and more shells of fusion develop until reaches Fe @which star collapses rapidly
Why does the mass transferred from a star to a compact companion end up orbiting the compact object in an accretion disk? What kind of radiation does the disk emit?
-Mass is squeezed inside small radius, leaving space for transferred mass to collect in swirling accretion disk, acting as holding tank for mass -Friction heats up disk, radiating optical UV light or even x ray -Layers rub against each other (viscosity) and emit visible/ultraviolet light
What is a meteor and what is a meteorite? Why is it interesting to study the chemical composition (elements) in meteorites?
-Meteor: flash of light seen when small, rocky object burns as it passes through atmosphere -Meteorite: rocky fragment that survives passing through the atmosphere and reaches the ground -Shows us relics of the early solar system and what it was composed of -Asteroid: leftover planetesimals in inner solar system (have moons) -Comets: leftover planetesimals in outer solar system
What, if any, properties of light you observe from a star or galaxy change, if the object is moving towards you? Moving away? Moving in the perpendicular direction ("sideways")?
-Moving toward you then shorter wavelength, blue shifted -moving away, longer wavelength: redshifted -sideways motion = no effect on wavelength
Why do neutron stars have a maximum possible mass, and what is its value in solar masses?
-Neutron degeneracy pressure cannot support a neutron star against gravity if its mass exceeds about 2-3 sm
Define the event horizon of a black hole in terms of Newton's theory of gravity. Describe it in terms of Einstein's theory of gravity (spacetime curvature). How big is a 1 M BH in km?
-Newton: EH is the distance (R) away from mass (m) where escape velocity > speed of light -Einstein: A massive object curves the spacetime around us, far from the object spacetime is nearly flat, close to the object the curvature forms a "well", Objects sense the curvature and are drawn into the well. For dense objects curvature increases until the sides are so steep that if something falls in it cannot get out. -3Km (3km times the mass in units of M.)
Einstein's theory of general relativity describes gravity in a fundamentally different way from Newton's theory of gravity. Describe and compare the ideas of each theory.
-Newton: gravity = force b/w 2 masses; in order for gravity to work, objects must have mass; photons have no mass, gravity shouldn't affect them -Einstein: presence of obj w/ mass creates curvature in spacetime; no need for 2nd mass; photons traveling thru space = bent bc spacetime is bent
What happens in a classical nova? What happens in a "thermonuclear" or Type Ia supernova? What type of compact star is present in both, and what elements are made in each?
-Nova: A modest amount of mass is transferred slowly onto a white dwarf from a binary companion. The surface heats up until it ignites in runaway H fusion reactions. The ensuing explosion blows the surface layers off the WD but does not destroy it -"WD thermonuclear SN": A larger amount of mass is transferred onto a white dwarf so that its mass exceeds the WD limit of 1.4 M ". The entire WD "goes up in flames," and is incinerated into heavier elements, including a good deal of Fe and Ni. This is a "Type Ia" supernova.
Where in our Solar System do we find most of the leftover planetesimals that did not get incorporated into major planet? (they are concentrated in multiple regions)
-Oort cloud, Asteroid Belt and Kuiper belt
Why are the inner four planets of our Solar System small and rocky, while the outer four planets are large and made of light materials including a lot of H and He gas?
-Protoplanetary disk nearest Sun is hotter, allows for condensation to occur -Formed by accretion of objects -Hotter than outer parts, metal and rock condense at higher temperatures -Jovian formed by gas accretion -Outside frost line it is cold enough for ice to form -Gravity of larger planets are able to hold and retain H and He -Two possible ways: Core accretion: solid cores formed first, gravity drew light gases Gravitational instability: disk develops lumps of gas, which collapse like the original solar nebula and do not have rocky cores
Why is the spectrum of the Cosmic Microwave Background (CMB) brightest (peak intensity) in the microwave part of the electromagnetic spectrum, instead of, say, in visible light? What kind of spectrum is it (thermal, emission line, absorption line)?
-Recombination- 378,000 -Inflation-<<1 -H fusion into He- -Destruction of most anti-matter- .001 -Emission of the CMB- 380,000
How do conditions in the central regions of the sun compare with those at the surface of the sun and why? (Where is it hotter/cooler, denser/ less dense, etc.?)
-Sun is hottest and densest at central regions; -Fusion provides the ongoing energy source to maintain the temperature and pressure.
How does the s-process differ from the r-process, and where do each of these reactions take place, according to the latest information astronomers have?
-The s-process or "slow process" involves neutrons being captured one at a time. It happens inside AGB stars -The r-process or "rapid process" involves the Fe nuclei being flooded with neutrons. This happens in merging neutron stars and possibly a core collapse supernovae from high mass stars
What observed properties of galaxy clusters provide evidence for the existence of dark matter spread over large regions of space?
-The velocities of galaxies orbiting within galaxy clusters, measured by doppler shifts, show more gravity than implied by stars -X-ray observations reveal large quantities of hot gas in giant galaxy clusters. Galaxies holding onto this gas as opposed to letting it evaporate gives a measurement for the amount of dark matter. -Gravitational lensing: galaxies appear warped and light rays look bent because they have to avoid dark matter
Qualitatively, What are the relationships between wavelength, frequency, and energy of light? That is, which properties are directly proportional to each other- increase or decrease together, and which are inversely proportional- increase/decrease in opposite directions?
-Wavelength and Frequency: inversely proportional -The greater the energy the larger the frequency and the smaller the wavelength
Why do the absorption lines and emission lines of a particular ion of a given element fall at the same wavelengths? What happens inside atoms to make emission and absorption lines?
-When an atom absorbs light the photon energy must be exactly equal to the energy needed to make an electron jump from a smaller orbit to a bigger one. -When an atom emits light, a photon is created, and the energy of the photon must be equal the energy lost by the atom when an electron jumps from one orbit to another
What causes the emission from pulsars to be seen as "pulses" that is, as blips of emission that repeat at regular intervals? Typically, how long are the intervals between pulses (periods)?
-When the beam is pointed at us we see a brighter star image or radio "blip" than when it has swept past our line of sight. -the radiation beam sweeps around like lighthouse because of the neutron star rotating on its axis. -millisecond to one second
For which pairs of astronomical objects (planets, galaxies, clusters of galaxies) is Hubble's Law valid, and under what circumstances does it NOT apply?
-applies to galaxies and clusters of galaxies -does not apply to objects bound together by gravity -Measures correlation of distances between galaxies and their recessional velocity based on redshifts/ Doppler shifts (so long as galaxies are not gravitationally bound to same group or galaxy cluster)
Why does a high-mass star face an "energy crisis" once the core has been converted to Fe? What happens to the core at that point and afterwards?
-bc no new energy producing fusion reactions possible, elements > Fe made by diff process -"Iron Catastrophe": bc Fe can't be fused, nuclei disintegrates into pieces, which also uses energy so thermal pressure fails triggering a collapse. Beginning of core collapse SN -Es and Ps forced together into dense core making neutrons: "neutronization" releases a neutrino -core collapse stopped by NDP, @ which point core = neutron star -upper layers fall onto core, rebound, go flying into space
What is the relationship between brightness and luminosity of a star? Which of these is an intrinsic property of stars, and which is relative because it also depends on the observer?
-brightness of star depends on luminosity & distance -Luminosity = intrinsic -Brightness = relative -Luminosity: total amount of power star radiates as light, amount of fuel it's burning up, depends on temp. and surface area -Brightness: amount of light we see
Explain the reasoning behind the Main Sequence turn off method for determine ages of star clusters. What kinds of stars are present in young clusters but not in old clusters? Are there any kinds of stars that should be present in old clusters but not in very young ones?
-clusters form w/ stars of all masses, most massive stars move off MS 1st, time passes and so do lower mass stars -cluster's age: MS lifetime of stars @ turnoff point; diff ages = diff turnoff points -young clusters = some high mass stars -older clusters = MS stars "peeled off"; WDs and RGs present
How do we determine the surface temperature of a star using it's continuous (thermal or blackbody) spectrum? How do we determine the temperature using spectral type, and what is the physical basis for this method (That is, why does it work)?
-cool star emits more red light than blue, appears red -warm star emits ~equal amounts of visible wavelengths, appears yellow-white -hot star emits more blue light than red, appears blue -Spectral Type tells: surface temp of stars thru absorption lines ranking HOT to COOL *look at study guide*
What is special about the alpha elements such as C,O,Ne,Mg, etc. that cause them to be the next most abundant elements in the universe after H and He?
-fused in the center of high mass stars after H and He
Why do protostellar clouds with less than .08M never become Main sequence stars?
-interior doesn't get hot enough for H fusion to begin before EDP stops them from further contraction -instead = brown dwarfs
List as many forms of energy as you can think of. Give a couple of different examples that illustrate one form of energy being converted and conserved into another type.
-kinetic, potential, radiative, rest-mass - PE to KE: ball gets thrown off a building -GPE to TE when a cloud contracts -mass energy = what'd be released if mass converted to energy -photosynthesis uses radiative energy (Light) to power chemical reactions
Describe the Main Sequence mass-luminosity and mass-lifetime relations (for larger masses, are they larger/longer or smaller/shorter?) What are the reasons for these trends?
-larger masses: shorter lifetime, large luminosity -Mass-Lum: larger masses = higher lum; lum inc w/ mass -mass-lifetime: MS lifetime = length of time star can stay on MS fusing H
Where is the mass of a black hole located, What is this location called, and what is its density?
-located in central singularity -density = infinite
What two measured stellar properties enable us to determine a star's radius regardless of whether or not it is a Main sequence star?
-luminosity and surface temp. -star w/ large luminosity, low surface temp must be physically large to compensate (Red Giant) -hot star, low luminosity must be small (White dwarf)
What is cosmological "inflation"? How was its effect different from the phenomenon we describe through Hubble's Law?
-nearly instant. blowing up of the distance scale -result: tiny quantum ripples scaled to enormous sizes; seeds for future structures -inflation no longer happening; dramatic event that happened all at once -hubble's law continues today
What force is required in order for the nuclei of elements heavier than H to exist? What force must it overcome?
-nucleus of an atom held together by strong nuclear force -overcome electromagnetic forces between protons in nucleus
What did the detection of any solar neutrinos tell us about the sun? Why did the results of the early experiments present a "problem", and what is the solution to the problem?
-results: only high energy neutrinos found, failed to find all kinds predicted -new detectors used GA detected some low energy neutrinos -SNO used heavy water to detect all neutrinos and prove they're changing type -solar fusion --> 1 type of neutrino, but 2 OTHERS EXIST -neutrinos tell us a lot about what's happening in sun's core, essentially fusion reactions occur
What is meant by the term rotation curve? What does the rotation curve of the Milky Way look like, and what does it tell us about the distribution of dark matter in our Galaxy?
-rotation curve: plot of orbital speed against distance -bc Kepler's 3rd law; orbital speed decrease w/ distance -Milky Way rotation curve not Keplerian; meaning enclosed mass changes w/ radius; more gravity present than accounted for -Most galaxies: flat rotation curve, large presence of dark matter in outer regions -immense amount of DM in our galaxy makes curve not keplerian
What are the Roche lobes of a binary star system?
-surface where 2 stars have equal influence; effects of 2 stars balance; anything @ "inner lagrangian" has equal GPE relative to both stars -Binary system stars interfere with each others evolution → material near both stars feel the force of both -Matter moving from one star to Lagrangian point can be captured by other star -If star is MS star, large enough to capture mass stream and collect transferred mass -donor star's roche lobe shrinks, mass runaway
What causes the periods of most pulsars to gradually increase (get longer) with time?
-synchrotron radiation -a loss of rotational energy due to radiation
What is a "planetary nebula"? What lies at its center, and what material makes up the nebula?
-the cast off layers of a former giant from low mass star -core = hot, central star: pre white dwarf
What indirect evidence that gravitational waves exist did we know about before LIGO (the Laser Interferometric Gravitational- Wave Observatory) was built?
-the strongest gravity waves will be produced by large masses experiencing high accelerations, Stars in a short period, tight orbits will radiate gravity waves that carry away orbital energy, causing their orbits to shrink and periods to shorten. -We see effects of this in binary systems with neutron stars. (why we don't see this very often)
Describe what happens in neutron capture reactions. What are the inputs and products?
-triple alpha process= first series of reactions which add He nuclei to create higher mass alpha elements that contain 4He -Fe = last possible output in standard fusion; after, heavier elements only created thru neutron capture reactions -slow "s" process: low mass stars, neutrons captured one at a time, followed by beta-decay which changes the element -rapid "r" process: high mass stars, Fe nuclei flooded w/ neutrons, makes neutron rich isotopes
Describe the traditional picture of galaxy formation by the collapse of a giant gas cloud.
1. A protogalactic cloud contains only hydrogen and helium gas 2. Halo stars begin to form as the protogalactic cloud collapses 3. Conservation of angular momentum ensures that the remaining gas flattens into a spinning disk 4. Billions of years later the star-gas-star cycle supports ongoing star formation within the disk. The lack of gas in the halo precludes further star formation outside the disk.
What (qualitatively) are the conditions inside giant molecular clouds? What are some of the most common molecules and why?
Molecular clouds are dense, dark and extremely cold; most common are H molecules in different chemical states (determined mostly by temperature) more abundant