AST201H1 Lecture Notes - Star Formation

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grayprairie-dog379

4 Apr 2011

School

UTSG

Department

Astronomy & Astrophysics

Course

AST201H1

Professor

Stefan Mochnacki

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AST201H1 Full Course Notes

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We can use the h-r diagram of a cluster to figure out how old the cluster is: look at a cluster, young stars: lots of gas and dust. Older no gas and dust from when it was formed: measure luminosity and spectral classes/surface temps. N the one that turns away form the main sequence closer to the bottom is the oldest cluster. N spectroscopy, hydrogen emits or absorbs a huge amount of red light. N dark region is a region of presence of a lot of gas and dust which blocks out gas and light (dust lane) N between the spirals balls of hydrogen balls and dust are related. N lots of blue stars lots of young stars. Most distant stars we can see are blue because although these stars are rare, they are extrememly luminous. N sentoras a, lots of gas, eating up another galaxy.

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).

Helium is very common in the Sun and calcium is rare. Why arehelium lines weak and calcium lines strong in the visible spectrumof the Sun?

How would a star regain its state of equilibrium if the energygeneration rate of a star were to become slightly smaller than itsequilibrium?

Why do metal poor stars have the most elliptical orbits? Fromwhere do they obtain their metals?

why do so few visual binary star systems been fully analyzedto reveal individual masses?

When we look at light curve for an eclipsing binary systemwith total eclipses, how can we tell which star is hotter?

Why do extremely cool stars look fainter than we might expectfrom their luminosities and distances?

Why can't we use solar type stars as spiral tracers? what typeof stars make good spiral tracers? why? What characteristics dothey have to perform this function?

in some old, dense stars, a few blue stars, known as bluestragglers are seen. why are blue stars unexpected in suchclusters? If stars that stick together mix their materialthoroughly when they collide, how might you explain such bluestars?

Supposed you jumped into a black hole feet first? what wouldhappen to you? what would your friends who stayed behind actuallysee?

Why are there different types of galaxies?

what is the eventual fate of the milky way galaxy? whatprocess will lead to this fate? can anything change this?

What are the processes that are responsible for the formationof an elliptical galaxy in comparison to a spiral galaxy? Whycannot galaxies evolve from elliptical to spiral and from spiral toelliptical?

Is it surprising that a pulsar is not seen in every supernovaremnant? why?

How do we form the conclusion that quasars are so vary faraway?

How many times longer does a .50 - M star fuse hydrogen atit's core than does a 1.5 - M star?

How many 0.75 - M main sequence stars would it take to equalthe luminosity of one 15 - M star?

A few multiple choice questions im having trouble with...

1. If a star formation switched off in a spiral galaxy, whichpartof it would get fainter? Bulge, disk, halo, dark matter orglobularclusters?

2. What is the essential difference between formation of spiralandelliptical galaxies?
a. random motions of stars are larger in ellipticals?
b. spiral galaxies had a more recent tidal encounter withanothergalaxy?
c. ellipticals form stars before they collapse; spiral formstarsafter they collapse?
d. spiral galaxies rotate faster
e. ellipticals had a more recent violent encounter withanothergalaxy?

3. The temperature of the background radiation is almost the sameinall directions
a. this is suprising, because the radiation from oppositedirectionsin the sky is comming from places that are beyong eachothers lighttravel horizon
b. this is expected because the big bang was a veryhomogenousexplosion
c. this was a measurement error in early observationsnowdiscredited.
d. the statement is not true, the temperature shows alargefluctuation all over the sky
e. none

thanks in advance!!!

AST201H1 Lecture Notes - Star Formation

AST201H1 Full Course Notes

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