Astronomy Exam #4

the Big Bang

(not an explosion) an expansion of the universe that brought space and time into existence, space itself began expanding from that time on -no one place/ it happened everywhere at the same instant of time -at the beginning there was only pure energy -no limit on how much space can expand -space is not hollow and not spherical -no center or edge of the universe

How old is the Milky Way? How old is our solar system?

-10 billion years and will remain active for another 10 billion years -approx. 4.5 billion years

The Great Debate (main players and outcome)

-April 26th, 1920 (it ended in a draw/tie) -Harlow Shapley= argued for only one galaxy (ours/the Milky Way) -Herbert Curtis= argued for many galaxies *7 months later Hubble proved Curtis was right

galaxy observations

-Hubble and Human got the speed/velocity of galaxies using the Doppler effect (redshift) -Hubble got the distance of galaxies using photos (used standard candle of cepheid variable stars and luminosity relation)

galaxy collisions (2 types)

-galaxies collide with each other to form irregular galaxies 1. merger=2 galaxies of similar size collide and combine to form one larger galaxy 2. galactic cannabalism= a small galaxy and a much larger one collide and the larger galaxy devours the smaller one

Will the universe end? How do we know?

-it will expand forever (but everything in it will eventually die) -by calculating the average density of matter in universe

Milky Way structural components (4)

1. disk= flat black streak (horizontal line thru galaxy) 2. bulge= puffiness near center of galaxy 3. halo= spherical shell where gravity has influence 4. spiral arms= sub-structures inside the disk; arcs of stars w/in the disk

3 possibilities for ultimate fate of universe

1. open universe= (we live in one) expands forever b/c there is not enough gravity to stop it 2. flat universe= expands forever but stops expanding after an infinite time b/c there is just enough gravity to stop it 3. closed universe= stops expanding and starts contracting (Big Crunch) b/c there is more than enough gravity-->leads to possibility of oscillating universe (multiple big bangs and big crunches)

parallel universes (5 different theories/types)

1. regions beyond the observable universe 2. inflationary universe=entire universe is expanding and ours is just one bubble of many popping into existence after big bangs 3. quantum multiverse= quantum mechanics says A. anything can happen, B. everything does happen, C. in some universe 4. simulated universe=simulated multiverse whose reality is nearly as complex as our own (more dimensions) 5. ultimate multiverse= every single theory that could possibly exist would have to exist in some form somewhere

4 major types of galaxies

1. spiral galaxies= have spiral arms w/in a disk emanating from a bulge, lots of gas/dust--> new stars are born and galaxy looks patchy 2. barred spiral galaxy- (the Milky Way) similar to spirals w/ a bar of stars running thru the bulge 3. elliptical galaxy= elliptical shape, no spiral arms/disk/halo/or bulge, little to no gas/dust, mostly red b/c of old stars 4. irregular galaxies= asymmetrical, sometimes just 2 galaxies colliding, they don't have spiral arms/disk/bulge/or halo but do have gas and dust

How large/what is the diameter of the Milky Way?

100,000 light-years

when did the Big Bang occur?

13.7 billion years ago

How do we know that we are located in a spiral arm?

Harlow Shapley (1917) discovered that globular clusters form a huge spherical system that is not centered on the earth

Hubble's law

V= H x D (recessional velocity= Hubbles constant x distance) noticed there was a linear relationship between recessional velocity and the distance to the galaxies

the Milky Way is not...

an active galaxy

Standard candle (What was Hubble's standard candle?)

an object that you know it's luminosity and can be used to find distance -Hubble used Cepheid variable stars

How many stars are in the Milky Way?

between 100-400 billion (using initial mass function)

How many galaxies are there?

billions and billions

local group

cluster of galaxies (our Milky Way is a part of this)

superclusters

clusters of galaxy clusters (largest physical structure that makes up the universe)

prediction of the Big Bang theory that was discovered

cosmic microwave background radiation= hot radiation left over all over the sky

What is responsible for the universe expanding?

dark energy

active galaxies (2 types)

galaxies that are pretty rapidly devouring something; powered by supermassive black hole 1. radio galaxy= 2 lobes of radio light on either side of the galaxy 2. quasars- young galaxies (redshifted/moving away) with supermassive black holes and the most distant/most luminous objects ever observed

gravitational lens

gravity from clusters of galaxies bends space and acts like a lens (bends/magnifies/distorts objects)

Which of the 4 structural components of the Milky Way have the oldest stars in the galaxy?

halo (contains globular clusters)

Suppose Hubble's constant were 2x as large as it is. The maximum age of the universe would then be?

halved

inflation (theory)

immediately after the Big Bang the universe expanded faster than the speed of light for a fraction of time-->parts of the universe are unobservable

Where in the Milky Way is our solar system located?

in a spiral arm about 26,000 light-years from the center

universe is...

isotropic=expansion looks the same everywhere (light from distant galaxies will always appear redshifted no matter where you are in the universe)

Hubble's constant is important to know b/c...

it directly relates to the age of the universe

recombination

occurred 380,000 years after the Big Bang and represents the time when atoms formed and persisted for the first time -1st elements produced=hydrogen, helium, and lithium-->formation of stars-->bigger elements

Milky Way

our galaxy, is a disk and forms a band around the sky, and has lots of gas and dust

Which of the 4 structural components of the Milky Way have the youngest stars in the galaxy?

spiral arms (contain open clusters and nebulae)

cosmology

study of the origin, structure, and evolution of the universe -Stephen Hawking=leading cosmologists who wrote "A Brief History of Time"

What does Hubble's law tell us about our universe?

that it is expanding b/c of the "Big Bang"

The most effective technique to find distances to galaxies is to look at objects in the galaxies for which we know?

the luminosity

lookback time

the time required for light to travel from an object/event to you

galaxies are carried farther apart b/c...

the universe is expanding

The primary reason that massive o-type (hot and blue) stars are not found in the halo is b/c they are?

to short-lived to move from the disk into the halo

Hubble's tuning fork diagram

way to classify galaxies based on there shape E= elliptical #'s=tell us shape (0=perfect sphere, 7=elliptical) S=spiral SB= barred spiral Irr=irregular letter's=tell us how tightly wrapped the arms are around the center (A=tightest, C=least tight) and the size of the bulge (A=biggest, C=smallest)

observable universe

what we can see (younger than 14 billion light-years away)

Olber's paradox

"why is the sky dark at night?" -solution=the universe is not infinitely old/ it has a finite age

dark matter

(can't directly see it) by observing the rotation of stars in galaxies, astronomers found that there is a lot of mass that is not luminous *the farther stars from the center of the galaxy move just as fast due to dark matter *about 96% of the energy and matter in the universe is dark