ASTR 1346:Chapter 12
111 Cards in this Set
| Front | Back |
|---|---|
|
Steps of Birth of a Star
|
1. protostar
2. pre-main sequence
3. main sequence
|
|
Microwaves are blocked by ___
|
water vapor & oxygen
|
|
Infrared is blocked by ___
|
water vapor & carbon dioxide
|
|
Ozone Layer blocks ___
|
ultraviolet, x-rays, gamma rays
|
|
Einstein showed that ___
|
energy of photon decreases with its wavelength
|
|
Photon Energy Formula
__ and __ observations show that space between the stars is not empty
|
infrared and radio
|
|
The matter between the stars
|
interstellar medium
|
|
Interstellar medium contains at least __% of all the known mass in our Galaxy
|
10%
|
|
Interstellar medium is made of two components -
|
gas and dust
|
|
Vast field of stars as well as dark regions due to interstellar gas
|
milky way
|
|
Very cold (less that 100) K
|
gas
|
|
Made up of mainly individual atoms and small molecules
|
gas
|
|
Mainly H and He
|
gas
|
|
90% of gas is made up of __
|
atomic or molecular hydrogen
|
|
9% of gas is made of ___
|
helium
|
|
1% of gas is made of ___
|
heavier elements
|
|
Spectrum shows that gas is generally ___
|
deficient in some heavy elements (carbon, oxygen, silicon, magnesium, iron) because these elements have gone to form the interstellar gas
|
|
Consists of clumps of atoms and molecules (like the ones that make up smoke or soot)
|
dust
|
|
Support for the theory that interstellar dust forms out of interstellar gas
|
infrared observations indicate that silicates, carbon, and iron, polycyclic aromatic hydrocarbons (PAHS)
|
|
Frozen mixture of water ice contaminated with trace amounts of ammonia, methane, and other compounds
|
dirty ice
|
|
Particles are basically spherical
|
gas
|
|
Individual particles are elongated but large scale structure is more complex
|
dust
|
|
___ blocks the light from stars
|
interstellar matter
|
|
Obscuration (blocking of light) is caused mainly by dust particles also called __
|
dust grains
|
|
Light can be obscured in two ways -
|
absorbed or scattered
|
|
Light can be obscured only by particles having diameters ___
|
comparable to or larger than the wavelength of radiation involved
|
|
The size of a typical dust grain
|
10-7m (0.1 µm)
|
|
The size of a typical dust grain is comparable in size to the ___
|
wavelength of visible light
|
|
Try to block the visible light
|
dust grains
|
|
Obscuration produced by particles of a given size increased with ___
|
decreasing wavelength (increasing frequency)
|
|
Blocked even more by dust grains
|
ultraviolet, x-rays, gamma rays
|
|
The general dimming of starlight by interstellar matter
|
extinction
|
|
Dust preferentially absorbs/scatters ___
|
short-wavelength radiation
|
|
___ of light from distant stars is obscured and scattered more than red
|
blue part of light
|
|
In addition to being generally diminished in overall brightness, stars also appear __ than they are
|
redder
|
|
Effect were stars appear redder than they really are
|
reddening
|
|
Not distributed uniformly. At some places its rarer, and at other places very dense in the form of giant clouds.
|
interstellar matter
|
|
Stars form from the ___
|
interstellar medium (giant molecular clouds - GMC)
|
|
Giant clouds of interstellar gas and dust
|
giant molecular clouds (GMC)
|
|
GMC's are made of mainly ___
|
molecular hydrogen (H2)
|
|
Because molecular hydrogen is hard to detect, radio astronomers search for ___
|
carbon monoxide (C0)
|
|
There are about ____ hydrogen molecules for every CO molecule
|
10,000
|
|
___ GMC's are estimated to exist in our galaxy
|
6,000
|
|
Diameter (size) of GMC
|
50 - 300 light years
|
|
Mass of GMC's
|
105 - 2 x 106 Msun
|
|
GMC's are ___ times the mass of the Sun
|
thousands of times
|
|
Temperature of GMC's
|
10-30 K
|
|
Density of GMC's
|
102 - 105 molecules/cm3
|
|
Density of GMC's are ___ times ___ than average density of interstellar matter
|
several thousand times greater
1. emission nebula
2. dark nebulosity
3. reflection nebula
4. dark nebula
5. emission nebula
|
|
Blocks the light from the background nebula IC 434
|
Horsehead Nebula
|
|
NGC 2023 is a ___ nebula
|
reflection rebula
|
|
Dust grains scatter the blue light from the stars more effectively than any other color, hence this nebula looks bluish
|
NGC 2023 (reflection nebula)
1. emission nebula
2. reflection nebula
3. dark nebula
|
|
Three kinds of nubulae
|
1. emission nebula
2. reflection nebula
3. dark nebula
|
|
A hot (O or B type) star illuminates a gas cloud
|
emission nebula
|
|
Excites and/or ionizes the gas (electrons kicked into higher energy states)
|
emission nubula
|
|
Emission Nebula are in ___ regions
|
HII regions
|
|
Electrons recombining, falling back to ground state produce __
|
emission lines (emission nebula)
|
|
Neutral hydrogen
|
HI
|
|
Singly ionized hydrogen
|
HII
|
|
Radiation from young O & B type stars has blown gas away from the center of nebula, causing gas to clump in dark globules where new star formation is taking place
|
emission nebula
the core of the Rosette Nebula (emission nebula)
NGC 2246 (emission nebula)
|
|
Star illuminates gas and dust cloud
|
reflection nebulae
|
|
Star light is reflected by the dust
|
reflection nebulae
|
|
Reflection nebula appears ___
|
blue
|
|
Why does Reflection Nebula appear blue?
|
blue light is scattered by larger angles than red light
|
|
What makes sky appear blue?
|
blue light is scattered by larger angles than red light
|
|
Stars not hot enough to ionize hydrogen in interstellar medium, instead, brightest stars produce a ____ as their light is scattered from interstellar dust
|
reflection nebula
reflection nebula
1. reflection
2. emission
|
|
Dense clouds of gas and dust that absorb light from the stars behind
|
dark nebulae
|
|
Appear dark in front of the brighter background
|
dark nebulae
dark nebulae
|
|
Stars from when the __
|
GMC collapses under its own gravity and breaks up into pieces
|
|
(4) Collapse in GMC is triggered (or stimulated) by:
|
- cloud-cloud collisions
- supernova blast wave
- starlight (shock waves) by nearby young, massive, hot O or B type stars (emission nebulae)
- density waves in spiral arms of a galaxy
supernova blast - Cygnus Loop
|
|
Triggers further star formation (second generation stars)
|
compression from shock waves around O & B type stars
1. emission nebula
2. newborn stars
3. interstellar cloud
4. expanding shock waves
5. first-generation stars
6. new, second-generation stars
|
|
Cloud unstable and triggers the gravitational collapse
|
contraction of GMC
|
|
Cloud fragments into smaller clumps. Clouds further fragment into more smaller clumps.
|
contraction of GMC
|
|
Depending on conditions, cloud may either produce a few dozen stars much larger than Sun or 100's or 1000's of stars comparable or smaller than our Sun
|
contraction of GMC
|
|
Contraction of GMC process takes ___ (time)
|
a few million years
|
|
The conditions of temperature, pressure and density under which a fragment of a gas cloud is forced to collapse under the influence of its own gravitational attraction
|
jeans instability
|
|
Formation of Protostar
|
GMC contracts and forms dense core of gas & dust called Bok globules
|
|
Condition under which gravitational forces overcome thermal forces (pressure due to heat)
|
jeans instability
|
|
In formation of protostar, dark region develops ___
|
jeans instability
|
|
Rapidly infalling gas and dust
|
young protostar
|
|
The central gases are heating as they fall into the newly forming protostar. Cooling is necessary before further collapse.
|
formation of protostar
cluster of protostars
|
|
As protostar grows in mass, its surface gets brighter while its core heats up
|
pre main-sequence star
|
|
When little gas is left in center of the dark core, the object becomes a ___
|
pre main-sequence star
|
|
Larger; can be observed by infrared only (not in visible)
|
protostars
|
|
1 solar mass MS star is ___ in its protostar stage
|
5 times larger
|
|
Matter falls towards the core and forms outer shell, radiation flows outside, gravity inside, and mass accretion stops.
|
protostar
|
|
Energy is generated by the gravitational contract
|
protostar
|
|
It may be visible to the outer world, but not called the star yet
|
protostar
|
|
Star contracts slowly, temperature increases
|
pre main-sequence star
|
|
107 nuclear fusion starts
|
pre main-sequence star
|
|
Balance between gravity and radiation; pressure establishes
|
pre-main-sequence star
|
|
The star is born
|
main-sequence star
|
|
Depending on ___ starts take different time to reach to main sequence, stay on main sequence for a different amount of time, die different death
|
mass
|
|
- Form fast
- Live fast, burn hot
- Leave main-sequence fast
- Die young, die explosively
|
high mass stars (O & B type stars)
|
|
- Form extremely slowly
- Stay on main-sequence for long time
- Leave main-sequence slowly and die gently
|
low mass stars (K & M type stars)
|
|
Never begin burning hydrogen because they are too small and don't generate enough heat
|
brown dwarfs
|
|
Example of Brown Dwarf
|
Jupiter
|
|
The minimum mass of gas needed to generate nuclear fusion
|
0.08 solar mass (80x mass of Jupiter)
|
|
Balance between pressure and gravity (no contraction or expansion)
|
hydrostatic equilibrium
hydrostatic equilibrium
|
|
Most of the stars (especially main sequence stars) are in the ___
|
hydrostatic equilibrium
|
|
Stars NOT in the hydrostatic equilibrium
|
forming stars
|
|
- They are contracting
- Gravity is overcoming pressure
|
forming stars
|
|
Protostar to main-sequence takes about ___ years
|
40-50 million years
|
|
Protostar to main-sequence time length is ____ than ___% of the Sun like star's lifetime on the main-sequence
|
less than 1%
|
|
Stars lifetime on the main sequence
|
10 billion years
|
|
Post main sequence
|
1. red giant
2. white dwarf
3. black dwarf
|
|
How much time of their entire life do stars spend on the main sequence?
|
any given star spends 99% of its life on the main sequence
|
|
What forces play important role in the main sequence stars to strike the balance?
|
balance between gravity (inward) and radiation (outward)
- hydrostatic equilibrium
|
|
___ overpowers star in pre-main-sequence stage
|
gravity
|
|
Our Sun is __ years old
|
5 billion years old
|
|
Our Sun is a ___ star
|
main-sequence star
|
ASTR 1346:Chapter 11