Astronomy Test 3

STUDY
PLAY

Terms in this set (...)

Star
A glowing ball of gas held together by its gravity and powered by nuclear fusion
Vital statistics of the Sun
Surface temperature is around 6000k
Radius is about 100 earths
Rotational period is about 24.9 days at equator- 29.8 at poles
*The sun is a main sequence star
Chemical composition of the sun
Mainly hydrogen (91%)
helium (8.7%)
(Also oxygen and carbon in very small percentages)
Structure of the sun from inside to out
Core
Radiation Zone
Convection Zone
Photosphere (what we see and salll the 'surface')
Chromosphere
Corona
Solar Wind
The solar interior
Standard Solar Model
We can't observe the solar interior directly
Mathematical models are developed to understand the interior that must fit observations and laws of Physic; they must explain the surface temperature of the Sun,etc using physics phenomena consistent with the conditions (like temperatures and pressures) predicted by the models
Helioseismology
Study of vibrations on the sun as a whole
Provides additional information to test mathematical models
Where is energy produced in the sun? (Where is the fusion occurring and what elements are involved?
Energy is produced in the core, where nuclear fusion of hydrogen to helium occurs
How does the suns energy get to the surface of the sun? (What makes the sun shine?)
Nuclear fusion
Temperature and density in the suns core
15 million K
160,000kg/m3
*Where fusion occurs
Sunspots
-Associated with intense magnetic field and cooler temperatures
- Come in pairs in the photosphere
Sunspot cycle
-An 11 year cycle in which the number of sunspots reaches a maximum and minimum
-Half the duration of the solar cycle
Solar cycle
- A 22 year cycle in which the Suns magnetic pole reverse and return to their original configuration
Fusion as an energy source
Fusion fuels the sun (hydrogen to helium)
Using E=mc2, 600 million metric tons/second is converted into energy
The sun must produce enough energy in its interior to replace the energy lost from its servce----> Fusion
Luminosity
How much light a star actually emits; an intrinsic property of a star, it does not depend in any way on the location or motion of the observer. It is sometimes referred to as the star's absolute brightness
Does NOT depend in any way on the location/motion of the observer
Apparent brightness
How bright an individual star appears in our sky; eh amount of energy striking per unit area per unit time of some light sensitive surface
Brightness Can be measured directly
The closer the star is, the brighter it appears
The farther the star, the dimer it appears
How is brightness related to luminosity?
Inverse square law
brightness=Luminosity/4πD^2
What variable can be measured directly?
brightness
If you know distance and brightness, what can you calculate?
Luminosity
If you know luminosity and brightness, what can you calculate?
Distance
Absolute Magnitude
Used to discuss luminosity
Apparent Magnitude
Used to discuss brightness
The lower the magnitude of a star..
The brighter the star is
EX: a magnitude 2 star is brighter than a magnitude star
Magnitude and brightness
A difference of 5 in magnitude represents a factor of 100 in brightness (EX: a magnitude 2 star is 100 times brighter than a magnitude 7 star)
Three techniques for determining distance
Parallax
Spectroscopic parallax
Variable star
Standard Candle
-Any technique using luminosity and brightness to calculate distance
-Goal of any standard candle technique is to find distance
Two types of standard candle techniques
Spectroscopic parallax
Variable star
Spectroscopic parallax
-Use of the spectroscopically determined luminosity and the observed brightness of a star to determine the star's distance
-Estimate luminosity by looking at temperature in HR diagram
Parallax
- The one direct method of determining distance (but you can only use it for nearby stars)
-Measures the position of a star
- The apparent shift in the position of one object relative to another object caused by changing perspective of the observer
Variable Star
-Variable stars change luminosity with time (they pulse), and you can use the period of the pulse (the longer the period the more luminous) to find the luminosity and in turn find distance
-Cepheid variable
-A star with varying luminosity, many periodic variables are found within the instability strip on the HR diagram
How is the mass of a star determined?
-Studying the stars orbit around a binary companion
- HR diagram
Keplers 3rd Law
Used for mass with binary stars
Wein's Law
Used for temperature with spectrum
A relationship describing how the peak wavelength and therefore the color of electromagnetic radiation from a glowing black body changes with temperature
Stefan-Boltzmann Law
Used for radius with L and T
Doppler effect
Used for radial velocity with spectrum
How is radial velocity determined?
Doppler effect and red/blue spectrum
Cool stars are...
Red
Hot stars are...
blue
Low mass stars are..
at the bottom bottom of the HR diagram and long life times
High mass stars are...
at the top of the HR diagram and have short life times
Left end of main sequence characteristics
stars are hotter, larger, more luminous and more massive than the sun
Right end of main sequence characteristics
stars are cooler, smaller, and fainter than the sun
HR Diagram
Main sequence
the strip on the HR diagram where 90% of stars are found. Main sequence stars fusing hydrogen to helium in their cores
Yellow giant or Horizontal Branch
A region on the HR diagram defined by stars burning helium to carbon in a stable core
Red Giant
Upper right quadrant
A low-mass star that has evolved beyond the main sequence and is now fusing hydrogen in a shell surrounding a degenerate helium core
White Dwarf
Lower left quadrant
The stellar remnant left at the end of the evolution of a low mass star
Made up of mostly carbon
*no fusing
If a main sequence star is more massive than the sun it is located..
to the upper left on the main sequence
If a main sequence star is less massive than the sun it is located..
to the lower right on the main sequence
What information tells you the most about a star?
Mass, tells you its life cycle
Red Dwarfs
Lower right region, a small old, relatively cool star on the main sequence
Brown dwarfs
a "failed" star that is not massive enough to cause hydrogen fusion in its core, an object whose mass is in between least massive stars and super massive planets (jupiter)
parsec
Unit of distance to a star
Magnitude= 3.3 light years
Evolution of a sun-like star
- When the sun runs out of hydrogen in the core, it will begin to burn hydrogen in a shell around the core. This will cause it to swell into a red giant
- After leaving the main sequence, low mass stars follow a convoluted path along the H-R diagram that includes the red giant branch (Up and to the right), the horizontal branch, the asymptotic branch, and a path across the top and then down to the lower left of the diagram
- Planetary nebulae form as the low mass star loses mass, eventually leaving behind a white dwarf
Life cycle of sun like star
1. Main sequence
2. Red Giant
3. Horizontal branch
4. Asymptotic Giant Branch
5. Planetary nebula ejection
6. White Dwarf
Types of fusion in each star/stage
Main sequence= hydrogen to helium
Red Giant= no fusion
Horizontal (yellow giant) branch= Helium to carbon
Asymptotic branch=no fusion
Planetary nebula= nothing
White dwarf= nothing
stars that burn hydrogen to helium are on______________
The main sequence
Fusion in the core of a red giant
No fusion
Fusion in the core of the horizontal branch
He---->C
life cycle of high mass star
- High mass stars fuse heavier elements than low mass stars and therefore have more violent deaths
- Evolving high mass stars leave the main sequence as they burn heavier elements, producing an iron core.
- Iron core eventually collapses and type 2 supernova explosion occurs
-Supernova explosion leaves behind a neutron star or a black hole
"Deaths" of stars
Low mass stars become white dwarfs

High mass stars experience supernova explosion after collapse of iron core and turn into either a neutron star (medium high mass stars) or a black hole (most massive stars)
Planetary nebula
The expanding shell of material ejected by dying red giant, stellar remnants after the death of stars
Nova
A stellar explosion that results from runaway nuclear fusion in a white dwarf in a binary system
Type 1a supernova
A supernova explosion in which no trace of hydrogen is seen in the ejected material. Most of these are thought to be the result of runaway carbon burning in a white dwarf star onto which material is being deposited by a binary companion
Type II supernova
-A supernova explosion in which the degenerate core of an evolved massive star suddenly collapses and rebounds
-How a high mass star dies
Neutron star
- The neutron degenerate remnant left behind by a type II supernova
-Remnants of high mass stars, only elementary parts are neutrons, incredibly dense (greater than mass of sun but the size of Waco)
Black hole
-Formed from the most massive stars type II supernova explosion
- An object so dense that its escape velocity exceeds the speed of light; a singularity in spacetime
Chandrasekhar limit
1.4 times the size of the sun (solar mass)
The upper limit on the mass of an object supported by electron degeneracy pressure
If a star is above 1.4 limit it is a...
neutron star
If a star is below the 1.4 limit it is a
White dwarf
What property tells you the most about a star and how it is going to evolve (its life cycle)?
Mass
< 10 solar mass stars become
white dwarfs
> 10 solar mass stars become
neutron stars or black holes