Final Exam Short Answers Flashcards
How old are Bright Stars in the Arms of a Spiral Galaxy?
Young.
Why don’t Spiral Galaxies ‘Wind Up’?
Outer parts orbit more slowly.
What is Important to Remember about Elliptical Galaxies?
No ongoing star formation - red and dead.
What Type of Galaxy is the Most Massive?
Elliptical.
What Causes Irregular Galaxies?
Disturbed by interactions with larger galaxies.
What are Active Galaxies?
Galaxies that generate energy at their cores.
What will Eventually Happen to all Galaxies in the Universe with no more Star Formation?
Only small, old stars left as part of elliptical galaxies.
How do Old Stars Return Gas to Interstellar Medium?
By supernova explosion or stellar winds.
Which Galaxies Form First and How?
Small galaxies form first and larger galaxies form from mergers.
What are the 2 Kinds of Matter?
Dust and Radiation.
What are the 3 Key Characteristics of Dust?
Not moving, no pressure, stars and galaxies.
What are the 3 Key Characteristics of Radiation?
Light speed, high pressure, redshifts with expansion.
How does Matter Progress with Heat?
Solid, liquid, gas, plasma, npe, quarks, ???
What Happened 10^-6 Seconds After the Big Bang?
Quark-hadron phase transition.
What does the Ratio of Protons to Neutrons depend on?
Temperature.
How do we Know Photon-Number Density?
Due to temp of CMB.
When did Primordial Nucleosynthesis Take Place?
First 3 minutes after the big bang.
Why did the Universe have to Cool Before Atoms could be Made?
Photons were too energetic - would make ions.
What was Recombination?
Universe cooling enough for H atoms to be stable, universe now transparent 380,000 years after big bang.
Who Discovered the Microwave Background?
Wilson and Penzias.
How was Microwave Background Discovered?
Accidentally using a satellite communications device.
What is the Temperature of the Microwave Background?
3 Degrees Kelvin.
What Happens to Photon Energy as the Universe Cools?
It drops.
What is the Ratio of Neutrons to Protons at Freeze Out?
1N : 7P.
What Happens to the Universe’s Temperature as it Expands?
It cools down.
How has the Composition of the Universe Changed?
Now: matter and dark energy
Then: radiation and particle physics
Who discovered Uranus?
William Herschel in 1781.
When was the Great Debate?
1920s.
When were the Rules of General Relativity Implemented?
1915.
How does Orbital Period Relate to Radius?
Year is proportional to radius ^1.5.
Why do Inner Planets Move Faster?
Speed is proportional to distance ^0.5.
Who Discovered Spiral Galaxies Move too Fast?
Vera Rubin (1975-80).
What are all Galaxies Embedded in?
A dark halo - 80% of its total mass.
Where do Galaxies Live?
In clusters and superclusters.
Why do Galaxies Cluster?
Dark matter - too many for chance gatherings, lots of “missing mass”.
What is Gravitational Lensing?
Light bent by gravity, distant images distorted.
What is Dark Matter Likely to be?
A fundamental particle.
Why can’t we Detect Dark Matter?
We are transparent to it and it is transparent to us.
What is the Hubble Flow?
Bound objects don’t expand.
What is Hubble’s Constant Roughly?
66.93.
How is Hubble’s Constant Measured?
Start with cepheids - measure close ones with parallax, or use supernovae.
What are Supernovae?
Exploding stars: briefly outshine an entire galaxy.
What are the 2 Types of Supernovae?
Type 2: Giant collapsing stars
Type 1a: Accreting white dwarf in a binary system.
What is the Chandrasekhar Limit?
Max mass of a white dwarf.
What does the Slope of Hubble’s Constant Line Tell us?
Hubble’s constant.
What does the Shape of Hubble’s Constant Line Tell us?
How to constant changes.
What Happens to Matter every time the Universe Doubles in Size?
Matter density drops by a factor of eight.
What will happen to our Local Universe in the Future?
Dark energy increases, Hubble’s constant stabilises, galaxies spread out (apparent motion speeds up), distant galaxies move faster than light, so only local group is visible.
When will M31 Merge with the Milky Way?
4 billion years.
What is Concordance Cosmology?
Big questions about nature and origin of dark sector.
How does Dark Energy Change as the Universe Expands?
Density doesn’t change.
What are the Basic Ingredients of the Universe?
Dark matter, dark energy, radiation, atoms (baryons) with a neutrino background.
