Chapter 20 cosmic perspective – Flashcards
Unlock all answers in this set
Unlock answersquestion
About how many galaxies in observable universe?
answer
over 100 billion galaxies
question
Age of most galaxies around us?
answer
10 billion years
question
How to study young galaxies?
answer
looking at rgeat distances
question
Cosmology
answer
study of overall structure and evolution of the universe
question
Three major types of galaxies
answer
Spiral, Elliptical, irregular
question
Spiral Galaxy
answer
flat white disks with yellowish bulges at their centers - usually display beautiful spiral arms
question
Elliptical Galaxy
answer
Redder, more rounded , elongated like football - contain very little cool gas and dust, contain very hot, ionized gas
question
Irregular Galaxy
answer
appear neither dislike or rounded - blobby star systems - contain young massive stars - megellanic clouds are examples
question
Why do the colors of galaxies differ?
answer
spiral/irregular galaxies appear white because they ave stars of all different colors and ages, elliptical galaxies have old, reddish stars that produce most their light
question
Dwarf Galaxies
answer
have as few as 100 million stars
question
Giant galaxies
answer
more than 1 trillion stars
question
disk component
answer
flat disk where stars follow orderly, nearly circular orbits around center - contains interstellar medium
question
How may disk components differ?
answer
molecular, atomic, and ionized gases in the interstellar medium may differ from one to the next
question
Spheroidal Component
answer
The bulge and Halo - orbits with many inclinations and contain little cool gas or dust
question
Bulges tend to extend how far?
answer
10,000 Light years
question
Barred spiral galaxies
answer
spiral galaxies that appear to have a straight bar of stars cutting across the center with spiral arms curling away from the ends of the bar
question
What do astronomers think our galaxy is?
answer
Barred spiral galaxies because our bulge appears somewhat elongated
question
Lenticular galaxies
answer
intermediate class between spirals and elliptical (they lack arms) tend to have less cool gas than normal spirals but more than ellipticals
question
Among large galaxies what percent are spiral or lenticular?
answer
75-85%
question
elliptical galaxies are sometimes known as?
answer
spheroidal galaxies
question
Elliptical galaxies lack a significant _______ component.
answer
Disk
question
Giant Elliptical galaxies
answer
relatively rare and are among the most massive galaxies in the universe
question
Dwarf Elliptical Galaxies
answer
fewer than a billion stars - often found new larger spiral galaxies
question
Gas in a giant elliptical galaxy:
answer
Low density, x ray emitting much like the gas in hot bubbles created by supernovae
question
Lack of cool gas in elliptical galaxy means:
answer
They have little to no star formation (like our own halo)
question
When were irregular galaxies more common?
answer
when the universe was younger
question
Hubbles Galaxy Classes
answer
organizes galaxy types into a diagram shaped like a tuning fork
question
E0 Galaxy
answer
Sphere
question
Hubble Galaxy Class Elliptical
answer
Designated by E and a number - Elliptical are on the handle at left - larger number/flatter disk
question
Hubble Galaxy Class Spiral
answer
S for ordinary spiral, SB for barred spirals followed by lowercase a, b, or c - bulge decreases size a-c
question
S0 (hubble class)
answer
Lenticular Galaxies
question
Irr (hubble Class)
answer
Irreglar Galaxes
question
Quantitative galaxy classification
answer
similar to H-R diagram for Stars - measures galaxy luminosity and galaxy color
question
Blue Cloud
answer
Major group - consists of spiral or irregular galaxies with active star formation
question
Red Sequence
answer
Consists galaxies that lack active star formation and are redder in color because they have few blue or white stars - most elliptical in shape
question
Groups
answer
spiral galaxies found in loose collections of up to a few dozen falaxies
question
Clusters of galaxies
answer
contain hundreds and sometimes thousands of galaxies extending over more than 10 million light years - elliptical
question
radar ranging
answer
how astronomers measure AU - radio waves are transmited from Earth and bounced of Venus
question
Standard Candle
answer
light source of a known, standard luminosity
question
Main-sequence fitting
answer
method of determining distances to different star clusters by comparing brightness to their main sequence stars
question
Cepheid Variable stars
answer
extremely luminous variable star
question
Henrietta Leavitt
answer
1912 - discovered Cepheid are closely related to their luminosity (longer the period, more luminous the star)
question
Period Luminosity Relation
answer
the longer the period, the more luminous the star
question
Cepheid vary in luminosity because:
answer
they pulsate in size, growing brighter as they grow larger and dimmer as they shrink -
question
The Great debate
answer
Held in Washington dc April 26 1960 - Shapley ( spiral nebulae were gas clouds internal to milky way) Vs Curtis (Kants island of stars)
question
What did Hubble discover about Andromeda?
answer
Using the 100 inch telescope at Mt Wilson he saw individual stars - he used Cepheid stars to calculate distance
question
redshifted
answer
object emitting radiation is moving away from us
question
Hubble's Law
answer
the formula that expresses the idea that distant galaxies move away from us faster
question
Hubble's constant
answer
H-naught
question
Two important difficulties when using hubble's law to measure galactic distances
answer
1 - galaxies do not object the law perfectly - nearly all galaxies experience gravitational tugs from other galaxies 2 - distance as only as accurate as best measurement of hubble's constant
question
Does hubble's law work for galaxies in the local group?
answer
No
question
Cosmological principle
answer
the idea that the matter in the universe is evenly distributed without a center or edge
question
Balloon analogy
answer
as the balloon expands, the dogs move apart in the same way galaxies move apart in our expanding universe
question
lookback time
answer
difference between current age of the universe and the age of the universe when light left the object
question
spacetime diagram
answer
a way to visualize the relationship bet ween distance, expansion and lookback time
question
cosmological redshift
answer
as the universe expands photo wavelengths shift to longer, redder wavelengths
question
cosmological horizon
answer
marks the limits of the observable universe (a boundary in time not space)
