Ch 23: The Milky Way Galaxy

Flashcard maker : Ruth Jones
In structure, our Milky Way is most similar to:
M-31, the Andromeda Galaxy
From the Sun, the distance to the Galactic Center is about:
8,000 pc
What two observations allow us to calculate the Galaxy’s mass?
the Sun’s orbital velocity and its distance from the Galactic Center
The circular but relatively flat portion of the galaxy is the ____
disk
The first portion of the galaxy to form was the ___
halo
A tightly packed group of a few hundred thousand very old stars is a
globular cluster
A ___ stands out in a photo of a galaxy because it shines brightly with light from massive young stars and glowing clouds of gas and dust.
spiral arm
Our Milky Way galaxy is a
spiral galaxy
Stars orbiting in the ___ near the galaxy’s center can have orbits highly inclined to the galactic plane.
bulge
Why are ionization nebulae so bright?
They are regions where gas is ionized by hot, young stars.
Galaxy
gravitationally bound collection of a large number of stars. The Sun is a star in the Milky Way Galaxy
Milky Way Galaxy
the spiral galaxy in which the Sun resides. The disk of our Galaxy is visible in the night sky as the faint band of light known as the Milky Way
Galactic disk
flattened region of gas and dust that bisects the galactic halo in a spiral galaxy. This is the region of active star formation.
Galactic bulge
thick distribution of warm gas and stars around the center of a galaxy
Galactic halo
region of a galaxy extending far above and below the galactic disk, where globular clusters and other old stars reside
Spiral nebula
historical name for spiral galaxies, describing their appearance
Spiral galaxy
galaxy composed of a flattened, star-forming disk component which may have spiral arms and a large central galactic bulge
Variable star
a star whose luminosity changes with time
Cataclysmic variable
collective name for novae and supernovae
Intrinsic variable
star that varies in appearance due to internal processes (rather than, say, interaction with another star)
Pulsating variable star
a star whose luminosity varies in a predictable, periodic way
RR Lyrae
variable star whose luminosity changes in a characteristic way. All RR Lyrae stars have more or less the same average luminosity
Cepheid variable
star whose luminosity varies in a characteristic way, with a rapid rise in brightness followed by a slower decline
Instability strip
region of the H-R diagram where pulsating post-main-sequence stars are found
Period-luminosity relation
a relation between the pulsation period of a Cepheid variable and its absolute brightness
Galactic center
the center of the Milky Way, or any other galaxy. The point about which the disk of a spiral galaxy rotates
Population I and II stars
classification scheme for stars based on the abundance of heavy elements. Within the Milky Way, Population I refers to young disk stars and Population II refers to old halo stars
Galactic year
time taken for objects at the distance of the Sun (about 8 kpc) to orbit the center of the Galaxy, roughly 225 million years
Tidal streams
groups of stars thought to be the remnants of globular clusters and even small satellite galaxies torn apart by our Galaxy’s tidal field
Thick disk
region of a spiral galaxy where an intermediate population of stars resides, younger than the halo stars but older than stars in the disk
Spiral arm
distribution of material in a galaxy forming a pinwheel-shaped design, beginning near the galactic center
Spiral density wave
Proposed explanation for the existence of galactic spiral arms, in which coiled waves of gas compression move through the galactic disk, triggering star formation
Self-propagating star formation
mode of star formation in which shock waves produced by the formation and evolution of one generation of stars triggers the formation of the next

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