libby final

the study of galaxies

galactic astrophysics

a collection of stars arranged into a more rounded shape near the center of a galaxy

galactic bulge

stars around the galactic disk (above and below)

galactic halo

the average duration of time it takes the Milky Way Galaxy to complete one rotation

galactic year

how long is a galactic year?

between 200 and 250 million years

streaming arcs of millions of stars swirling around the center of a spiral-disk galaxy

spiral arms

are spiral arms permanent structures?

no

the two major spiral arms of the Milky Way Galaxy

• Perseus Arm

• Scutum-Centaurus-Crux Arm

minor spiral arms of the Milky Way Galaxy

\- Norma Arm \n - Carina-Sagittarius Arm \n - Orion Arm

which spiral arm is our solar system located in?

the Orion Arm

variations in stellar concentrations that propagate throughout all the stars in the Milky Way Galaxy

spiral density waves

how far away is our solar system from the Milky Way Galaxy's galactic center?

roughly 25,000 light-years (8 kiloparsecs)

how wide is the Milky Way Galaxy?

roughly 100,000 light years in diameter (30 kiloparsecs)

how thick is the Milky Way Galaxy?

roughly 1,000 light years in thickness (300 parsecs)

how many star systems make up the Milky Way Galaxy?

roughly 100 billion star systems

the study of the shape and evolution of a galaxy

galactic dynamics

a black hole that has spent billions of years gaining more and more mass

supermassive black hole

what is the mass of a supermassive black hole?

millions of solar masses, sometimes billions

what is at the center of every major galaxy?

a supermassive black hole

a graph of the orbital speed of stars around the center of a galaxy as a function of their distance from the center of the galaxy

rotation curve

what kind of rotation curve does every major spiral galaxy have?

a flat rotation curve

dark matter distributed over an enormous sphere surrounding all the star systems of a galaxy

dark matter halo

how much of the universe is made up of dark matter?

roughly 90%

what does the theory of Massive Compact Halo Objects (MACHOs) say?

dark matter is an enormous number of brown dwarf stars in the galactic halo surrounding all the other stars of a galaxy

what does the theory of Weakly Interacting Massive Particles (WIMPs) say?

dark matter is composed of exotic quantum-mechanical particles (Supersymmetric Relativistic Quantum Field Theory)

very diffuse gas that fills the entire galactic disk

interstellar medium

an area in interstellar medium that is more dense than average

diffuse nebula

a diffuse nebula that absorbs light

absorption nebula

what color do absorption nebulas appear as?

black

a diffuse nebula that emits light

emission nebula

what color do emission nebulas appear as?

red

a diffuse nebula that reflects light

reflection nebula

what color do reflection nebulas appear as?

blue

the fraction of anything in the universe that is hydrogen

hydrogen fraction

what is the hydrogen fraction for nearly everything in the entire universe?

roughly 75%

the fraction of anything in the universe that is helium

helium fraction

what is the helium fraction for nearly everything in the entire universe?

roughly 25%

the fraction of anything in the universe that is not hydrogen or helium

metallicity

stars inside the galactic disk with higher metallicity

Population I stars

what is the metallicity of Population I stars?

1% or 2%

stars outside of the galactic disk with some metallicity

Population II stars

what is the metallicity of Population II stars?

roughly 0.1%

the very first stars born in the entire universe made up of solely hydrogen and helium

Population III stars

what is the metallicity of Population III stars?

0%

the process that causes light that gets to us to be more red than the original light

reddening

a star cluster inside the galactic disk

open star cluster

what type of stars make up open star clusters?

mostly Population I stars

a star cluster outside of the galactic disk

globular star cluster

what type of stars make up globular star clusters?

mostly Population II stars

what are properties of Population I stars?

hot, luminous, and blue

what are properties of Population II stars?

cool, dim, and red

what is the shape of open star clusters?

irregular

what is the shape of globular star clusters?

spherical

how many stars make up open star clusters?

several hundred

how many stars make up globular star clusters?

hundreds of thousands

where do you have to look in order to look towards the center of our Milky Way Galaxy?

in the direction of the constellation Sagittarius

young open star clusters embedded within the diffuse nebula from which they formed

embedded star clusters

star clusters with a significant number of O-type and B-type stars

OB associations

a cavity hundreds of light years across that surrounds OB associations

superbubble

the area in the sky that is in the direction of the "milky way" in the sky, opposite of the constellation Sagittarius

galactic anticenter

where is the galactic anticenter located?

near the intersection of the constellations Auriga, Gemini, and Taurus

a galaxy that orbits another galaxy

satellite galaxy

where did SN1987A occur?

in the Large Magellanic Cloud

what are the main satellite galaxies of the Milky Way Galaxy?

• Canis Major Dwarf Galaxy

• Sagittarius Dwarf Galaxy

• Small Magellanic Cloud

how far away is the Canis Major Dwarf Galaxy?

roughly 25,000 light-years (8 kiloparsecs)

how far away is the Sagittarius Dwarf Galaxy?

roughly 75,000 light-years (25 kiloparsecs)

how far away is the Large Magellanic Cloud?

roughly 150,000 light-years (50 kiloparsecs)

how far away is the Small Magellanic Cloud?

roughly 200,000 light-years (60 kiloparsecs)

a list of one hundred and ten faint objects in the sky

Messier deep sky catalog

M1 on the Messier catalog

the Crab nebula

what type of nebula is the Crab nebula?

a supernova remnant

M13 on the Messier catalog

the Hercules cluster

what type of star cluster is the Hercules cluster?

a globular star cluster

M31 on the Messier catalog

Andromeda Galaxy

the closest major galaxy to the Milky Way Galaxy

Andromeda Galaxy

how far away is the Andromeda Galaxy?

roughly 2.5 million light-years (800 kiloparsecs)

what type of galaxy is the Andromeda Galaxy?

a spiral-disk galaxy

how large is the Andromeda Galaxy?

roughly the same size as the Milky Way Galaxy

M33 on the Messier catalog

Triangulum Galaxy

how far away is the Triangulum Galaxy?

roughly 3 million light-years (over 800 kiloparsecs)

what type of galaxy is the Triangulum Galaxy?

a spiral-disk galaxy

how large is the Triangulum Galaxy?

roughly 1/10th the size of the Milky Way Galaxy

M42 on the Messier catalog

the Orion nebula

what type of nebula is the Orion nebula?

a diffuse nebula

M45 on the Messier catalog

the Pleiades cluster

what type of star cluster is the Pleiades cluster?

an open star cluster

M57 on the Messier catalog

the Ring nebula

what type of nebula is the Ring nebula?

a planetary nebula

variable stars in a star cluster that are protostars

Tauri variable stars

variable stars in a star cluster that are asymptotic-giant-branch stars

Cepheid variable stars

variable stars in a star cluster that are horizontal-branch stars

Lyrae variable stars

an equation relating the average luminosity of Cepheid variable stars with their pulsation period

Leavitt period-luminosity relation

the 3 major galaxies in the Local Galactic Group

• Milky Way Galaxy

• Andromeda Galaxy

• Triangulum Galaxy

how many galaxies are in a typical galactic group?

several dozen

how many major galaxies are in a typical galactic group?

less than 10

how many major galaxies are in a typical galactic cluster?

several hundred

how many galaxies are in the Local Galactic Group?

several dozen

how many major galaxies are in the Local Galactic Group?

3

an enormous region between galactic superclusters that is nearly completely empty of galaxies

cosmic void

what do multiple galaxies clumped together form?

a galactic group or galactic cluster