Exam #3 Flashcards
how is a star’s distance measured?
Light year (9.5 trillion kilometers, 5.8 trillion miles)
What is a Parsec (pc)?
a star’s parallax is equal to one arc second- about 3.3 light years
Luminosity
brightness (magnitude)
absolute magnitude
Measuring stars
-the amount of radiation leaving a star per unit of time
-measured in solar units
-Sun =1
the luminosity of a star
-the brightness of a star appears to have, related to the distance
-measures on the absolute magnitude scale
-Sun = -26.7
The apparent brightness (magnitude) of a star
-a stars apparent magnitude when viewed an 10pc
-Sun = 4.8
Absolute Magnitude
-Spectral classes- classified by spectral signatures, from decreasing temperature
-O,B,A,F,G,K,M
-O is very hot, M is cooler
-Sun is a G class star
Measuring Temperature
-measure in radius compared to the sun
-Sun = 1
Stellar Size
-Shows the relation between stellar Brightness (absolute magnitude) and temperature
-Made by plotting (graphing) each star’s luminosity (brightness) and temperature
Hertzsprung-Russell Diagram
-Main-sequence stars
-Giants (or red and blue giants)
-Super Giants
-White Dwarfs
Parts of an H-R Diagram
-90% of all stars
-band through the center of the H-R diagram
-sun is in the main sequence
-Red and dwarfs- lower-right of the H-R diagram
Main-sequence stars
-very luminous
-large
-red -upper-right of the H-R diagram
-Blue- Upper-left of the H-R Diagram
Giants (or red and blue giants)
-very large giants
-only a few percent of all-stars
-very top of the H-R diagram
Super Giants
Fainter than main-sequence stars
* Small (approximate the size of Earth)
* Lower-central area on the H-R diagram
* Not all are white in color
* Perhaps 10 percent of all stars
White dwarfs
mass/volume
Density
Stars that fluctuate in brightness
Variable Stars
-pulsating variables
-eruptive variables
types of variable stars
-fluctuate regularly in brightness
-expand and contract in size
pulsating variable stars
-explosive event
-sudden brightening
-called a nova
eruptive variable stars
2 stars orbiting around a common center of mass
Binary Stars
-visual binaries
-spectroscopic binaries (most common)
-eclipsing binaries (much rarer)
types of binaries
separated enough to be observed
visual binaries
-too distance to be resolved as 2 distinct stars
-detected by back-and-forth Doppler shifts of their spectral lines
Spectroscopic binaries
observed by the decrease in starlight intensity as a member passed in front of the other
eclipsing binaries
-cloud of dust and gases- nebula
Interstellar Medium
between the stars
the vacuum of space
-bright nebulae
-dark nebulae
-planetary nebulae
Types of nebulae
-glows if it is close to a very hit star
-emission nebula
-reflection nebula
bright nebulae
-not close to any bright star
-appear dark
-contains the material that forms stars and planets
dark nebula
– Less diffuse than other nebulae
– Originate from remnants of dying Sun-like stars
planetary nebulae
two opposing forces in a star are
gravity-contracts
thermal nuclear energy-expands
stars exist because of
gravity
-birth
-protostar
-main-sequence
-Red Giant
-burnout and death
stellar evolution stages
in dark, cool, interstellar clouds
-gravity contracts clouds and temperature rises
-radiates long-wavelength (red) light
-becomes a protostar
birth
-gravitational contraction of gaseous cloud continues
-core reaches 10 million K
-hydrogen nuclei fuse
-become helium nuclei
- the process is called hydrogen burning
-energy is released
-outward pressure increases
-outward pressure balanced by gravity pulling in
-star becomes a stable main-sequence star
protostar
-Stars age at different rates
-massive stars use fuel faster and exist for only a few million years
-small stars use fuel slowly and exist for perhaps hundreds of billions of years
-90 percent of a star’s life is in this stage
Main-sequence stage
-hydrogen burning migrates outward
-star’s outer envelope expands
-surface becomes red
-core is collapsing as helium is converted to carbon
-eventually all nuclear fuel is used
-gravity squeezes the star
Red Giant Stage
-final stage depends on mass
-possibilities
-low-mass star- .5 solar mass, red giant collapses, becomes a white dwarf
-medium-mass star- between .5 and 3 solar masses, red giant collapses, planetary nebula forms, becomes a white dwarf
-massive star- over three solar masses, red giant supergiant, H-He-C-O-Ne-Mg-Si-Fe, terminates in a brilliant explosion called a supernova, interior condenses, may produce a hot, dense object that is either a neutron star or a black hole
burnout and death stage
-small (some no larger than Earth)
-dense
-can be more massive than the sun
-spoonful weighs several tons
-atoms take up less space
-electrons displaced inward
-called degenerate matter
-hot surface
-cools to become a black dwarf
White Dwarf
-Type I
-Type II
Supernovae
- involves two objects
-a sharp rise in brightness followed by a steady, gradual decline
Type I Supernova
- involves one object
-a sharp rise in brightness followed by a “plateau” of emission months after the peak outburst
Type II Supernova
-forms from a more massive star
-star has more gravity
-squeezes itself smaller
-remnant of a supernova
-gravitational force collapses atoms
-electrons combine with protons to produce neutrons
-small size
-pea size samples weigh 100 million tons, same density as an atomic nucleus
-strong magnetic field
Neutron Star
-more dense than a neutron star
-Schwarzschild Radius: critical radius at which the escape speed equals the speed of light
-intense surface gravity lets no light or event escape, known as the event horizon
-as matter is pulled into it, it becomes very hot and emits X-rays
-likely candidate is Cygnus X-1, a strong X-ray source
Black Hole
-Spiral Galaxy (barred)
-Glactic Disk consists of a thin plane of matter that flattens to the galactic bulge at the center
-galactic halo: roughly spherical ball of faint old stars
structure of the galaxy
-about 400 billion stars
-100,000 light year wide
-13,000 light year thick
-sun is about 25,000 light year from the galactic center
-sun is located 100 billion times that of the sun, potentially accounted for by dark matter
-Sagittarius A star” a potential black hole at the galactic center
survey of the galaxy
-spiral galaxy
-barred spiral galaxy
-elliptical galaxy
-irregular galaxy
4 basic types of galaxies
-arms extending from nucleus
-about 30 percent of all galaxies
-large diameter up to 125,000 light years
-contains both young and old stars
Spiral galaxy
-stars arranged in the shape of a bar
-generally quite large
-about 10 percent of all spiral galaxies
barred spiral galaxy
-ellipsoidal shape
-about 60 percent of all galaxies
-most are smaller than spiral galaxies; however, they are also the largest galaxies known
elliptical galaxy
-lacks symmetry
-about 10 percent of all galaxies
-contains mostly young stars
-includes magellanic clouds
irregular galaxy
-group of galaxies
-some contain thousands of galaxies
-local group- our own group of galaxies, contains at least 28 galaxies
-supercluster- huge swarm of galaxies, may be the largest entity in the universe
galactic clusters
-galaxies that exhibit high luminosity, are very energetic
active galaxies
-active galaxies emitting high amounts of energy in the radio spectrum at large distances called lobes
radio galaxies
-the most powerful and luminous active galaxies
-exhibit a very high redshift (very distant)
Quasars or quasi-stellar objects
galaxies frow in size by the merging of smaller galaxies
Hierarchical formation
galaxies can morph by colliding with or interacting with other galaxies
galaxy evolution
study of the universe, including its properties, structure, and evolution
cosmology
strings of galaxy clusters
filaments
large areas where few galaxies reside
voids
The universe is
-Homogeneous- the same everywhere
-isotropic- the same in all directions
cosmological principle
the recessional speed of galaxies is proportional to their distance
-recessional velocity= Ho x distance
Hubble’s law/ expanding universe
-most galaxies exhibit a red doppler shift
-moving away
-far galaxies have greatest shift
expanding universe
-model that most accurately describes birth and current state of the universe
-cataclysmic explosion 13.7 billion years ago
-accounts for other galaxies moving away from us
-universe was once confined to a “ball” that was supermassive, dense, and hot
big bang theory
cosmic force proposed to be responsible for the acceleration of the Universe (Hubble expansion)
dark energy
final fate depends on the average density of the universe
-if the density is more than the critical density, then the universe would contract
-current estimates point to less than the critical density and predict an ever-expanding, or open, universe
fate of the universe
