MULT10011 Lecture Notes - Lecture 27: Black-Body Radiation, Star Cluster, Planetary Nebula

144 views2 pages

viridiankangaroo295

15 Jun 2018

School

University of Melbourne

Department

MULT

Course

MULT10011

Professor

Geoff Mcfadden, Christian Reichardt

For unlimited access to Class Notes, a Class+ subscription is required.

L.E.U - Lecture 27

Birth of stars and galaxies, and the life cycle of stars

Gravitational cascade

• starts small → tiny gravitational pull towards slightly denser regions

o space nearly flat

• increases more with time → as ore ass falls ito dese area, gravitatioal

attraction increases

o slope gets steeper

• with time, gravitational collapse becomes runaway process → in regions of very high

density, galaxies and stars form

o cluster of galaxies – initially fairly homogeneous, end state is very clumpy

forming a star

• cloud of gas collapses under its own weight

o cloud mostly made of hydrogen and helium but is contaminated by heavier

elements formed in supernovae explosions

• as cloud collapses, spin increases, dense object forms at its core – collapse heats gas

• if density and temp at centre f cloud become high enough, thermonuclear burning or

fusion will start → i.e. star will begin to shine

• thus a star is simply a hot ball of gas → more massive the star, the hotter it shines

• mass is key property of a star; it sets: how hot it burns, how long it lasts, how it dies

blackbody radiation

• each curve is characterised by a single temperature, T

• no matter what an object is made of, if it has a temperature T, it will have the same

blackbody spectrum

o spectrum of radiation is called the blackbody curve

the family of stars

• one of the most useful classifications is the Hertzsprung-Russell diagram, which plots

luminosity against temperature for each star

• location on main sequence is

completely determined by the

stars mass

• other stars off the main sequence

show stars at later times in their

evolution

stellar evolution

1. star forms as a gas cloud collapses

2. then burns hydrogen in its core

3. then burns hydrogen in outer shells

4. star throws off outer shells as a

planetary nebula

5. forms a white dwarf

find more resources at oneclass.com

Unlock document

This preview shows half of the first page of the document.
Unlock all 2 pages and 3 million more documents.

Already have an account? Log in

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).

MULT10011 Lecture Notes - Lecture 27: Black-Body Radiation, Star Cluster, Planetary Nebula

Get access

Related Documents

AST-0009 Lecture Notes - Lecture 8: Main Sequence, Red Giant, White Dwarf

ASTRON 1101 Lecture Notes - Lecture 20: Cno Cycle, Kilogram, Brown Dwarf

ASTR 1150 Lecture Notes - Lecture 5: Protoplanetary Disk, Orion Nebula, Protostar

Related Questions