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Galaxies
ch 10
41
Astronomy
Undergraduate 1
11/10/2008

Additional Astronomy Flashcards

 


 

Cards

Term

A galaxy contains...

Definition
contains... millions of billions of stars, gas, dust, and black holes
Term
three major types of galaxies
Definition

1. elliptical

2. spiral

3. irregular

Term
elliptical galaxies
Definition

a galaxy that is round or elliptical in outline and contains

  • little gas and dust
  • no disk or spiral arms
  • few hot, bright stars
Term

spiral galaxies

Definition

a galaxy with an obvious disk component containing..

 

  • gas
  • dust
  • hot, bright stars
  • spiral arms
Term
irregular galaxies
Definition

a galaxy with a chaotic appearance

large clouds of gas and dust

both pop I and pop II stars

with spiral arms

Term
Barred spiral galaxy
Definition

a spiral galaxy with an elongated nucleus resembling a bar from which spiral arms originate

 

2/3 of galaxies (including ours)

classified in three groups: SBa, SBb, SBc

Term
Large and small magellanic cloud
Definition

an irregular galaxy

visible in the southern sky

that is a satellite of our Milky Way galaxy

Term
two standard candle methods
Definition

1. Cephid method (period-luminosity relation)

2. Type 1a supernovae (collapse of an accreting white dwarf in a binary system)

Term
standard candle
Definition
object of known brightness that astronomers use to find distance
Term
Distance ladder
Definition
the calibration used to build a distance scale reaching from the size of Earth to the most distant visible galaxies
Term
type 1a supernovae are better to use in measuring very long distances than Cepheid variable stars because....
Definition
... type 1a supernovae are more luminous
Term
compared with spiral galaxies, elliptical galaxies lack (2 things)...
Definition

... lack hot, bright stars

... lack visible gas and dust

Term
Look-back time
Definition

the amount by which you look into the past when you look at a distant galaxy

 

a time equal to the distance to the galaxy in lightyears

Term
Hubble Law
Definition

 

 

galaxies in distant superclusters are moving away with recession velocity proportional to their distance

Term
The Hubble Law proves that...
Definition

proves that the universe is expanding

 

by estimating distances to galaxies

Term
Hubble Constant
Definition

a measure of the rate of expansion of the universe

 

the avg value of velocity of recession divided by distance = 70 km/Mpc

Term
How did Edwin Hubble prove that there are other galaxies far outside the Milky Way?
Definition
Hubble's measurement of the distance to the Cepheid varibles in the Andromeda Galaxy demonstrated that it was not a nearby nebula but an island of stars very far away.
Term
Rotation Curve Method
Definition

a method of determining a galaxy's mass by observing the orbital velocity

 

 

Term
how are galaxies distributed in the universe?
Definition
_ are not distributed in isolation, but in clusters and superclusters
Term
Rich galaxy cluster
Definition

a cluster containing over 1000 galaxies

 

mostly elliptical

 

scattered over a volume of about 3 Mpc in diameter

Term
Poor galaxy cluster
Definition

an irregularly shaped cluster that contains less than 1000 galaxies

 

many are spiral

no giant ellipticals

not condensed toward center

Term
Local group
Definition
the small cluster of a few dozen galaxies that contain our Milky Way
Term
What happens when two galaxies collide or merge?
Definition

their clouds of gas and dust colide, creating shock waves which trigger a tremendous amount of star formation

 

stars are so far apart that they rarely collide

Term
two effects of colliding galaxies
Definition

tidal tail

 

ring galaxy

Term
starburst galaxy
Definition

a galaxy undergoing a rapid burst of star formation

 

very rich in gas and dust

 

bright in infrared

Term
tidal tail
Definition
a long streamer of stars, gas, and dust torn from a galaxy during its close interaction with another passing galaxy
Term
ring galaxy
Definition

a galaxy that resembles a ring around a bright nucleus

 

result of a head-on collision of two galaxies

Term
galactic cannibalism
Definition
the theory that large galaxies absorb smaller galaxies
Term
active galaxy
Definition

a galaxy whose center emits large amounts of excess energy- often in the form of radio emission

 

suspected to have massive black holes in centers in which matter flows

 

 

Term
how big are active galaxies
Definition

approx the size of our solar system

Term
three types of active galaxies
Definition

1. peculiar galaxies

2. seyfert galaxies

3. BL Lacertae objects/blazars

Term
peculiar galaxies appear to..
Definition
appear to be blowing themselves apart
Term
seyfert galaxies
Definition

an otherwise normal spiral galaxy with an unusually bright small core that fluctuates in brightness

 

believed to indicate that the core is erupting

 

strong emission lines

Term

BL Lacertae objects

 

aka blazars

Definition

type of active galaxy

 

have featureless spectra with brightness that can vary by a factor of 15 in a few months

Term

Blazar

 

aka Bl Lac objects

Definition

objects that resember quasars,

 

thought to be highly luminous cores of distant active galaxies

Term
double lobed radio source
Definition
a galaxy that emits radio energy from two regions (lobes) located on opposite sides of the galaxy
Term
quasars
Definition

small, powerful source of energy believed to be the active core of a very distant galaxy

 

these galaxies are very bright (100Xlum)

with supermassive BH

traveling away from us at far speeds

 spectra highly redshifted

probably normal stars

Term
unified model
Definition
an attempt to explain the different types of active galactic nuclei using a single model viewed from different directions
Term

evidence for supermassive black hole to be cause for energy source..

Definition
...huge rotation near the centers of active galaxies and high-velocity jets ejected along their axes of rotation
Term
our milky way might have erupted as a...
Definition
quasar in the past when gas and dust were more plentiful
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