Exam 4 Flashcards
Bright, sphere-shaped region of stars that occupies the central few thousand lightyears of the milky way galaxy
Galaxy’s Bulge
Gas and Dust that lies between the stars in the Milky Way Galaxy
Interstellar medium
Two smaller galaxies that orbit the Milky Way Galaxy
Magellanic clouds
The continuous recycling of gas in the galactic disk between stars and the interstellar medium…
Star-Gas-Star Cycle
What is 2% of the mass of the milky ways interstellar medium?
Elements heavier than hydrogen and helium
Subatomic particles that travel close to the speed of light
Cosmic Rays
What is the most abundant chemical in molecular clouds?
H2
What does interstellar dust mostly consist of?
Microscopic particles of carbon and silicon
A cloud of hydrogen and helium that contracts to become a galaxy
Protogalactic Galaxy
Most stars in the Milky Way Galaxy are…
very old
A colorful cloud of gas that glows because it is heated by light from nearby hot stars
Ionization Nebula
Most common form of gas in the disk of the Milky Way Galaxy
Atomic Hydrogen Gas
What law of nature explains why the galaxy began to rotate rapidly and flattened out as it shrunk in size?
Law of Conservation of Angular Momentum
The circular but relatively flat portion of the galaxy
Disk
First Portion of the galaxy to form
Halo
A tightly packed group of a few hundred thousand, very old stars
Globular Cluster
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
Stars orbiting in the _____ near the galaxy’s center can have orbits highly inclined to the galactic plane
Bulge
Estimated number of galaxies in our observable universe
100 Billion
NOT one of the major clusters
Global Clusters
Dark energy has been hypothesized to exist in order to explain…
Observations of galaxies suggesting the expansion of the universe is accelerating
Dark Matter in inferred to exist because…
We can observe it’s gravitational influence on visible matter
Strong evidence for the existence of dark matter comes from the observations of…
Orbital Periods (rotation curve) of stars in the milky way galaxy
What is meant in cosmology by “critical density”?
The density that determines whether the universe expands forever or re-collapses
Why do we think galactic collisions were more common in the past?
The early universe was smaller, therefore galaxies were closer to each other in the past
What do we think lies at the center of the universe?
Cosmology tells us there is no center
Which type of galaxy contains very little interstellar gas?
Elliptical
What does the big bang theory predict could be seen today?
Radiation that is coming from all directions in space, and has been red-shifted to microwave spectrum
Using powerful telescopes to look back in time over 10 billion years, what did we discover the most distant (youngest) galaxies to look like?
Very Irregular
What is the rotation curve of a spiral galaxy?
A plot of the rotation (orbital) speeds of its stars vs. distance from the center of the galaxy
{TRUE OR FALSE} When we look at the cosmic microwave background radiation, we are looking further into space (back in time) than when we loom at the farthest galaxies
True
Matter fall into super-massive black holes in the centers of some galaxies is thought to be the source of:
Active Galactic Nuclei, Strong Radio Sources, Giant jets that shoot far into space, and Quasars
{TRUE OR FALSE} A main goal of the Hubble Space Telescope was to measure the Hubble Constant, H0 as 1/H0 to give us the best estimate of the current age of the universe
True
About how old was the universe when galaxies appeared?
1 Billion Years Old
A light source of known luminosity
Standard Candle
Where do we think fark matter primarily resides in our galaxy?
In the Halo region and it’s surroundings
Why have astronomers recently determined that there must be an additional strong force, termed “dark energy” acting on the universe?
They have measured an unexpected acceleration in the expansion
{TRUE OR FALSE} The existence of dark matter has been established by observing it with specialized dark matter telescopes
False
What is currently believed to make up the majority of dark matter?
WIMPS
About what age is the universe?
14 Billion Years Old
What TWO things happen when galaxies collide?
Strong gravitational forces will distort the shape of the galaxy and Molecular gas clouds will collapse. creating star bursts that enhance star formation
Cosmological red-shift that all distant galaxies exhibit is result of…
The expansion of the Universe
{TRUE OR FALSE} The sun is a bulge star, born near the center of the galaxy
False
What do we mean when we talk about the “expansion of the universe”?
That space itself is expanding
{TRUE OR FLASE} Starburst galaxies have been forming stars at the same furious pace since the universe was about a billion years old
False- Bursts of star formation would use up all the gas in a galaxy in a much shorter period of time than the age of the universe
What holds the Local Group of galaxies together?
The gravitational force
The luminosity of a Quasar is generated in a region about the radial size of…
Our solar system
How long does light from the neatest star (not including the sun) take to reach us?
About 4 years
What doe we think lies at the center of the Milky Way?
A massive black hole
How did Edwin Hubble first prove that the strange looking spiral nebulae were really distant galaxies?
He used bright Cepheid variables in them to measure their distances
When we look at a very distant galaxy, billions of light years away, we see it…
When it was younger than now
How long does it take for light to cross the milky way?
Around 100,000 years
Where are most of the milky ways globular clusters found?
In the halo
Where would you be most likely to find an ionization nebula?
In the disc
The orbits of halo and bulge stars are special because…
Their orbits are randomly inclined to the disk of the galaxy
Currently, where are stars born in the Milky Way?
Density waves in the disc spiral arms
Which form of radiation passes most easily through the disk of the Milky Way?
Infrared Light
How many stars do we think there are in our Milky Way Galaxy?
100 Billion
Why do disc stars bob up and down as they orbit the galaxy?
Because the gravity of other disc stars pull them towards the disc
