PHYS 1000 Lecture 12: Chapter 12 Notes

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tanbuffalo207

12 Feb 2018

School

University of Windsor

Department

Physics

Course

PHYS 1000

Professor

Mr.Mark Lubrick

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Document Summary

Du(cid:396)i(cid:374)g its sta(cid:455) o(cid:374) the (cid:373)ai(cid:374) se(cid:395)ue(cid:374)(cid:272)e, a(cid:374)(cid:455) flu(cid:272)tuatio(cid:374)s i(cid:374) a sta(cid:396)"s (cid:272)o(cid:374)ditio(cid:374) a(cid:396)e (cid:395)ui(cid:272)kl(cid:455) (cid:396)esto(cid:396)ed; the sta(cid:396) is in equilibrium. Eventually, as hydrogen in the core is consumed, the star begins to leave the main sequence. Its evolution then depends on the mass of the star: low mass stars go quietly: high-mass stars go out with a bang (high-mass stars = more than 8 solar masses) E(cid:448)e(cid:374) (cid:449)hile o(cid:374) the (cid:373)ai(cid:374) se(cid:395)ue(cid:374)(cid:272)e, the (cid:272)o(cid:373)positio(cid:374) of a sta(cid:396)"s (cid:272)o(cid:396)e is (cid:272)hanging. Stage 8: the core hydrogen has been largely depleted and we get a core of helium forming. The temperature is not hot enough for helium fusion. As the fuel in the core is used up, the core begins to collapse. The collapsing core heats the core temperature and causes the remaining hydrogen fusion to speed up. This increases pressure and causes the outer layer (envelope) to expand to about 3 times its normal size.

Related Questions

1. The Jeans instability occurs when
Athe pressure in a gascloud is less than its gravitationalforce.
Bthe pressure in a gascloud is greater than its gravitationalforce.
Cthe temperature in acollapsing cloud is hot enough to fuseHydrogen.
Dthe temperature in acollapsing cloud is hot enough to fuse Helium.

2. At what stage in its life does a star pass through theprotostarphase?
AAfter condensationbut before nuclear reactions begin in itscore.
BWhile it is convertinghydrogen into helium in its core.
CAfter nuclear reactionsend in its core, but before the red giantphase.
DWhen it is expanding insize as a red giant or supergiant.

3. The characteristics of an open cluster of stars are
Aa few hundredmembers, often very young and still embedded in thegas and dustfrom which they were formed.
Bmany thousand members, ofdifferent ages.
Ca few dozen members, theremnant of a globular cluster of starsfrom which most of themembers have escaped.
Dhundreds of thousands ofmembers, all very old, and no or verylittle interstellar gas anddust.

4. What is a protostar?
AA star near the endof its life, before it explodes as asupernova.
BA sphere of gas aftercollapse from an interstellar cloud butbefore nuclear reactionshave begun.
CA small interstellarcloud, before it collapses to become astar.
DA shell of gas left behindfrom the explosion of a star as asupernova.

5. What is an H II region?
AA region of hot,ionized hydrogen around one or more O and Bstars.
BA region of molecularhydrogen inside a giant molecularcloud.
CA region of neutral,atomic hydrogen in interstellar space.
DA region of gas and dustformed by the explosion of a massive star.

6. The total time that the Sun will spend as a main sequencestaris
Aabout 4.5 millionyears.
Bat least 200 billion yearsyears.
Cabout 1 millionyears.
Dabout 10 billionyears.

7. How is a star's lifetime related to its mass?
AThe lifetimes ofstars are too long to measure, so it is not knownhow (or if) theirlifetimes depend on mass.
BA star's lifetime does notdepend on its mass.
CLower-mass stars runthrough their lives faster and have shorterlifetimes.
DHigher-mass stars runthrough their lives faster and have shorterlifetimes.

8. In the Hertzsprung-Russell diagram, how does the position ofatypical star change while it is at the main sequence phase ofitsevolution?
AA star's position onthe main sequence is determined only by itsmass and not its age,and so, stars do not move along the mainsequence duringevolution.
BMassive stars (4 solarmasses) move toward the upper left as theirluminosity increases,while lower-mass stars move toward the lowerright as theirtemperature decreases.
CStars move from upperright to lower left while they are on themain sequence.
DStars move from upper leftto lower right while they are on themain sequence.

9. Why does the core of the Sun contain more helium andlesshydrogen than does the surface of the Sun?
AHelium condenses moreeasily so, when the Sun was forming the corebecame helium-rich;vast quantities of hydrogen were added onlyafter the core becamemassive enough.
BThe hydrogen has beenlifted out of the core by the Sun's magneticfield.
CHelium is heavier thanhydrogen, and has sunk toward the center ina process of chemicaldifferentiation.
DThermonuclear reactionshave converted much of the originalhydrogen in the core intohelium.

10. In terms of nuclear reactions, what is the next stage ofastar's life after the end of hydrogen burning in thecore?
AHydrogen burning ina thin shell around the core.
BHelium burning in thecore.
CCarbon burning.
DDeath (it becomes eithera supernova or a white dwarf).