Astro Lecture 2 Flashcards
(15 cards)
What are the steps to understanding the universe’s evolution?
Step 1: Determine what the universe is made of, its mean density, and how quickly it’s expanding.
Step 2: Use this information to predict the universe’s past and future behavior.
What are the three key features of the Big Bang model?
Homogeneous, Expanding, Very hot and dense at early times.
What does ‘homogeneous’ mean in cosmology?
The universe looks statistically the same everywhere on large scales.
No special places in the universe; homogeneous over enormous volumes of radius ~300 million light-years.
What is Hubble’s Law?
V = H × d.
Velocity of galaxy recession is proportional to distance, implying universe has a finite age of approximately t = 1/H.
What is cosmological redshift?
Light from distant galaxies becomes redder as it travels through expanding space.
Not the same as Doppler shift; atomic absorption lines move to longer wavelengths.
What did astronomers discover about the universe’s expansion in 1998?
The expansion of the universe is accelerating, leading to the concept of dark energy.
Earned Brian Schmidt (and others) the Nobel Prize.
How do we know the early universe was hot and dense?
Theory: Rewinding the expanding universe leads to a denser, hotter state.
Evidence: Cosmic Microwave Background radiation (CMB).
What is the Cosmic Microwave Background (CMB)?
Remnant radiation from the primordial fireball, nearly perfect blackbody radiation at 2.7K.
Tiny fluctuations (few parts in 100,000) show early structure.
What happened when the early universe cooled to about 3000K?
Electrons and protons combined to form hydrogen.
Photons could freely travel (universe became transparent).
These photons became the CMB we observe today.
What are the three main components of the universe by mass?
Ordinary/baryonic matter (~5%), Dark matter (~25%), Dark energy (~70%).
What is dark matter?
Matter that interacts gravitationally but doesn’t emit light.
Evidence includes galaxy rotation curves and gravitational lensing; makes up about 25% of the universe.
What is dark energy?
Mysterious component causing accelerated expansion.
Doesn’t behave like ordinary matter; makes up about 70% of the universe.
What evidence supports the existence of dark matter?
Galaxy rotation curves (stars move faster than visible mass would predict), gravitational lensing shows more mass than we can see.
Galaxy cluster dynamics require additional mass.
What are some current efforts to detect dark matter?
Underground laboratories like the Stawell Underground Physics Lab.
Looking for new particles that interact weakly with normal matter.
How are astronomers studying dark energy?
Using galaxies as tracers to study universe expansion.
Projects like the Dark Energy Spectroscopic Instrument (DESI); mapping the cosmic web at different distances/times.
