| ane | v = Hod | Hubble'south Police force, relates the recession velocity of a milky way to its distance from Earth. Ho here is Hubble'southward constant, approximately 75 (km/s)/Mpc |
| 2 | P = E/t | Ability equals energy per unit time |
10 corresponds to P21.ii
| 1 point | PROBLEM ane Why does the Globe seem to be at the heart of the Hubble expansion? The Earth appears at first glance to be the center of the universe's expansion considering all galaxies are moving away from us. However, because the speed at which those galaxies are receding from us is proportional to their distance, the same would be true for any other galaxy, also. Or, put some other way, if an astronomer in whatever other galaxy were to measure out the redshift of galaxies that he could see, he would come across the same relationship between recession velocity and altitude that nosotros see here. This is similar to the balloon expansion demo done in class.
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| Problem 2 If the universe is airtight, describe the reults that some future scientist like Edwin Hubble would obtain when he or she looked through a telescope during the period of wrinkle. Would other galaxies exist visible? Would they display a redshift? |
| 1/ii point | If a futurity scientist were to study galaxies during the contraction, he or she (or it, hey, they don't accept to be human) would obtain results that are the opposite of those Hubble discovered. All of the galaxies would be moving TOWARD the Globe. Their velocity would nonetheless be proportional to their distance, only this time the Direction would exist the contrary of the Hubble case. |
| i/four point | The other galaxies might or might non be visible, depending on how much time has elapsed between now and the observations. If the universe is but simply barely airtight, or it only has very slightly over the amount of mass necessary to cause the universe to contract, and then a lot of time, hundreds of billions of years at least, will laissez passer between now and when the universe turns around and starts to contract again. If this is the case, then the universe might already be well on the way to heat expiry by the fourth dimension the wrinkle really gets going, with all of the stars reduced to blackness dwarfs and invisible. However, if there is ample mass to close the universe, so the path to the big crunch will begin relatively soon and the galaxies will exist visible to a future observer. |
| 1/four signal | The galaxies volition not exist redshifted, they will be blueshifted, or shifted up in frequency (downward in wavelength) because of their movement toward the observer.
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| 1/10 point each | PROBLEM three Outline the major events for the current big bang model of the evolution of the universe. Life of a Universe I. The Large Blindside
a. Earlier 10-43s: all 4 fundamental forces unified.
b. 10-43south: gravity splits off from the other forces.
c. 10-35s
one. Potent nuclear force splits from electroweak force.
two. Matter forms preferentially over antimatter in the form of quarks and electrons.
3. Aggrandizement?
d. 10-10due south: nuclear weak and electromagnetic forces split.
due east. 10-5s: quarks course nucleons (protons and neutrons).
f. i.8 * 102due south: nucleons grade atomic nuclei.
thou. ii * ten13s: recombination one. Electrons and nuclei form atoms
2. Matter and radiations are decoupled, universe becomes transparent. II. Electric current universe
a. Galaxies form -- we're not quite sure just when this happens, nosotros know its after recombination, but equally we go along looking further and further abroad, we go on seeing older and older galaxies. The edge, along with the first forming galaxies, has yet to be discovered.
b. ane.2 * 1010 years: present day.
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| i/3 bespeak each | Trouble iv What are the fates of an open, airtight and flat universe? - Open universe: not enough mass to halt expansion, expands forever.
- Apartment universe: just enough mass to halt expansion, simply non enough to initiate contraction -- heat death.
- Closed universe: more than than enough mass to halt expansion, universe contracts toward big crisis.
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| Trouble v: If a galaxy is 500 Mpc (megaparsecs) away, how fast volition it exist receding from us?  This 1's a plug-and-chug into the Hubble relation, equation ane in a higher place. five = Hod
5 = 75(km/due south)/Mpc * 500Mpc
v = 37500 km/s
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| ane signal | 3.75 * 104 km/s
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| 1/2 each | PROBLEM six How tin can we talk about the evolution of stars over billions of years when human beings have been observing stars for only a few thousand years? There are two ways the evolution of stars over such huge timescales can be studied over a much shorter time period. The showtime is theoretical: in one case stars' power sources were discovered it became possible to create belittling and computational models of stars and their evolution over time. These models are based, however, on observations. Although nosotros can't follow a single star through its unabridged lifetime, we Tin observe many divide stars, each at a dissimilar phase of their development. From the proto-planetary disks that HST discovered in the Orion nebula, through T-Tauri stars and other phases of star formation, to primary sequence stars like the sun, to red giants like Betelguese, and finally to white dwarfs similar Sirius B and supernovae like SN1987A, stars can be plant that can be pieced together to form a coherent picture of what a single star's entire lifetime might await like.
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| 1/3 signal for each italicized aspect | PROBLEM 7 What are some differences between a larger star and a smaller star? This is a poorly worded question, information technology should read "what are some differences betwen a MORE MASSIVE star and a LESS MASSIVE star?". More massive stars are hotter, brighter(both while on the primary sequence merely), and alive less long than less massive stars. If a star has enough mass, it will eventually fuse elements heavier than Hydrogen, and if it has more than than almost eight solar masses it will become supernova after creating iron in its core.
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| i/two each | Trouble viii What is meant past "hydrogen burning" in the Lord's day, and why does it take to take identify in the centre of the sun? "Hydrogen burning" refers to the nuclear reaction of many protons combining to course Helium (called fusion), which in the procedure liberating energy. Fusion requires very loftier temperatures and pressures, and only occurs in the center of the sun because the centre is the just location at which these contditions exist.
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| 1/nine for each phase, interior, or surface | PROBLEM 9 Outline the evolution of a star similar to the Sun from its main-sequence phase to its white dwarf stage. For each significant step, briefly describe and distinguish the concrete conditions in the interior of the star, and those properties that are observed on the surface of the star. Life of a one Solar Mass Star | Phase | Timescale | Interior | Surface | | main sequence | 1010 years | Hydrogen fuses to Helium | yellow(5800K), 1.3*10vikm across | | red giant | few ten6 years | Helium fuses to Carbon, temp higher than for main sequence | ruddy (~3000K), about 1AU in radius | | white dwarf | few 1010 years | no fusion, exterior held up past degeneracy force per unit area | white (~x,000K), about 10,000km in diameter, cools slowly over the rest of the historic period of the universe |
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| PROBLEM ten If the Sun shines for xi billion years at its nowadays energy output, how much full energy will the star send into infinite during its lifetime? Here we'll simply rearrange equation 2 and get the total energy past multiplying the power times the time. Be careful to convert 11 billion years into seconds, since a Watt is a Joule/s. P = Due east/t
E = Pt
E = 4.24*x23kW * ane.1*x11years
Eastward = 4.24*1026J/s * 1.1*10xiyears * iii.15*107s/yr
Remember to convert kW to Westward, too. |
| 1 betoken | E = 1.v * 1045 Joules |
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Source: http://barnesos.net/~jbarnes/nats102/HW4/
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