Final Exam Flashcards
Spiral galaxy
Disc shaped like the Milky Way
Old stars in bludgeon, new stars in disc
Low mass ones have fluffy, loose arms and a small bulge
High mass ones have tight arms and a huge bulge
Elliptical
Fuzzy ball of stars
Mainly old stars (NOT forming new stars)
Range in masses from tiny to large
Irregular
Oddly shaped- can be dwarf irregular or merging
Dwarf irregular: small and low mass, lots of new stars, still forming stars
Merging irregular: stars don’t hit each other, gas clouds hit and make new stars. Settle down into elliptical galaxy
Gravity can…
Bend light, focus it like a lens, and magnify more distant objects
Which observation helped us learn that most of the Milky ways mass is dark matter?
Stars and gas orbit the galaxy too fast to be bound by the mass of the visible matter
What is the best analogy for how stars orbit the disk of the Milky Way?
The disk is like a ring of Saturn, since each particle orbits Saturn independently depending on keplers laws
Which observation helped us learn that the sun isn’t at the center of the Milky Way?
We see more globular clusters on the sky in one direction, rather than being evenly spaced
List the parts of the galaxy in the order that they form
Nucleus and halo at the same times disk, spiral arms
Dark matter is difficult to observe because
It doesn’t absorb or emit any light at all
Most of the mass of a cluster of galaxies is
Dark matter
What is a quasar
A galaxy with a very active and very bright supermassive black hole
Distance ladder
The distance to stars near the sun in the Milky Way are measured with parallax (let us get luminosities)
Won’t work at great distances, rest of Milky Way and other galaxies are measured with standard candles
Hubbles law
More distant galaxies are moving away faster, light is redshifted
More distant galaxies have higher redshift
We see a galaxy as younger than it actually is right now
Cosmic web
Clusters of galaxies arranged on a large scale in filaments and empty voids
Most of the mass is dark matter
We can’t see it, we infer it
When we’re galaxies making the most stars
When the universe was 1-5 billion years old
What does bubbles law relate?
Distance and speed at which it is moving away from us
In the first 5 minutes of the universe when fusion was everywhere, what was fusing?
Hydrogen into helium (and a little bit of other stuff)
Photons in the CMB came from
Plasma glowing because it is hot, when the atoms formed
The atoms in your body heavier than iron were probably made
In supernovae when massive stars died
How much of the milky ways total mass is dark matter?
90%
Astronomers were able to measure the mass of the Milky Way by watching stars and applying what law?
Keplers law
Watch the orbit speed and orbit size to measure the mass that makes it orbit
How did we learn where the sun is in the Milky Way?
By mapping the location of globular clusters in the sky
Over time the slight amounts of heavier elements in the galaxy’s gas increase due to
Stars forging heavy elements in their cores and spreading that material into their deaths
Most stars form in the spiral arms of the disk because
Gas in the disk enters the arms, slows down, and gets compressed
Astronomers suspect dark matter is probably made of
Particles that don’t interact with the electromagnetic force
What is the strongest evidence for the existence of dark matter in the Milky Way?
Stars orbit at about the same speed regardless of how far they are from the nucleus of the galaxy, suggesting there is a lot of invisible mass
The best analogy for the spiral arms of the Milky Way is
A traffic jam, where stars slow down due to the higher gravity of more mass
Compared to other spiral galaxies, the Milky Way is
About average size
Some galaxies shoot huge powerful narrow jets of high speed particles into space which are detectable at radio wavelengths. Astronomers think these jets are launched by
The accretion disk of a supermassive black hole at the center of the galaxy
What happens when galaxies collide?
The gas clouds hit each other, and new stars form from that gas
After large galaxies merge, what kind of galaxy is usually the result?
Elliptical
If you looked at the rate galaxies make stars and compare this rate at different times in the universes history, you would find the most stars being made
When the universe was a few billion years old
If you see a large ___ galaxy, you can assume it hasn’t experienced any big mergers
Spiral
The first galaxies had __ metalicity compared to the Milky Way as it is now
Much lower
Lost the galaxies in order of star formation rate from making the LEAST stars to making he MOST
Elliptical, spiral, irregular
Difference between stars currently forming in the Milky Way and the stars currently forming in a dwarf irregular galaxy?
The Milky Way newborn stars will be higher metalicity than the dwarf irregular stars
Observing what helps you learn more about the first galaxies?
A redshirt 7 galaxy
The farther away object
If you want to observe an overweight white dwarf go supernova, what should you study?
A nearby elliptical galaxy
How do astronomers know how galaxies change over time?
They ran computer simulations and compared them to observations of galaxies at different distances
Why did the most massive galaxies form first?
Their dark matter halos had more mass, which pulled in more gas faster
What ended up “killing” the large elliptical galaxies?
They used up all their gas and couldn’t make new stars
If you looked at the total energy of matter, dark matter, and dark energy in the universe you’d find that our universe is made of
Mostly dark energy
Based on observations and models, astronomers are fairly confident the universe is about
14 billion years old
The expansion of the universe is like
Stretching an infinite piece of elastic, where the space between things increased but it’s not expanding into anything else
The fate of the universe (recolapse, big chill, big rip) is determined by the balance between
Gravity trying to collapse everything and dark energy pushing everything apart
If the universe were recollapsing, we should see distances to supernovae and galaxies…
Getting smaller
The earth is at the center of
… nothing
What observations do astronomers make to determine the expansion of the universe?
The brightness and redshift of distant supernovae
If gravity is exactly the same strength as dark energy, then our universe would
Eventually stop expanding
Astronomers estimate that our universe is
Expanding and the rate of expansion is accelerating
All of the elements in your body heavier than hydrogen and helium were made
By generations of stars living and dying in the Milky Way
The amount of hydrogen, helium, lithium, and deuterium in the universe was determined when
5 minutes after the Big Bang, during universe wide fusion
