final ah Flashcards
Structure of the Milky Way
Components: Disk (spiral arms, stars, gas, star formation), Bulge (center with older stars), Halo (spherical area with old stars, globular clusters, no star formation).
Spiral Arms: Stars and gas are concentrated in arms. Star formation happens as gas clouds are squeezed in spiral arms.
Rotation: Stars and gas orbit the galactic center. Smaller orbits move faster (differential rotation), and stars in the disk mostly orbit in the same direction.
Types of Galaxies
Spiral: Flattened, with a central bulge, halo, and spiral arms. Active star formation in the arms (blue stars), old stars in the bulge/halo.
Elliptical: No spiral arms, mostly old stars, little gas, no star formation, usually found in clusters.
Irregular: No clear shape, neither spiral nor elliptical.
Measuring Cosmic Distances
Parallax: Used for nearby stars; distance = 1 / parallax angle.
Standard Candles: Objects with known luminosities used to measure distance (e.g., Cepheid variables, white dwarf supernovae).
Cepheid Variables: Pulsating stars whose period of variation helps determine distance.
White Dwarf Supernovae: Explosions with a consistent luminosity, useful for measuring large distances.
Hubble’s Law & Universe Expansion
Hubble’s Law: Galaxies move away from us, and their speed is proportional to their distance (V = H × d).
Redshift: Shift of light towards red, indicating galaxies are moving away.
Age of Universe: Calculated using Hubble’s constant.
The Big Bang & Early Universe
Hot and Dense: Early universe was hot, dense, and full of radiation.
Evidence for the Big Bang: Universe is expanding, cosmic microwave background (CMB) radiation, and the correct abundance of elements.
Cosmic Microwave Background (CMB)
Origin: Afterglow of the Big Bang, detected as microwave radiation.
Uniformity & Fluctuations: The CMB is uniform but has small fluctuations, which help explain the structure of the universe.
Electromagnetic Spectrum
Order: Gamma-ray, X-ray, UV, Visible, Infrared, Microwave, Radio (GXUVIMR).
Spectral Types: OBAFGKM (from hottest to coolest stars).
Inflation Theory
Inflation: The universe expanded rapidly right after the Big Bang, explaining the observed flatness and uniformity of the universe.
Dark Matter’s Role: Inflated the universe and caused it to evolve into its current structure.
Dark Matter & Evidence
Dark Matter: Non-luminous mass inferred from its gravitational effects on galaxies. Makes up about 90% of the Milky Way’s mass.
Evidence: Galaxy rotation curves (flat curves indicate dark matter), galaxy clusters, gravitational lensing, and x-ray observations.
Dark Matter and Large-Scale Structure
Galaxy Formation: Dark matter’s gravity helped form galaxies and clusters. Maps show superclusters and voids.
WIMPs: Weakly interacting massive particles, a possible candidate for dark matter.
Universe’s Expansion & Dark Energy
Expansion: The universe is expanding and accelerating due to dark energy.
Dark Energy: An unknown form of energy causing the expansion to accelerate, making the universe expand forever.
Contents of the Universe
Composition:
4.4% ordinary matter, 26% dark matter, 74% dark energy. Universe is 13.7 billion years old.
Habitable Planets & Life
Habitable Zone: The region around a star where liquid water could exist on a planet’s surface. Conditions for Life: Liquid water, energy, and nutrients are necessary for life.
Drake Equation
Purpose: Estimates the number of technologically advanced civilizations in the Milky Way.
Formula: N=Rtotal×L, where Rtotal is the rate of star formation and L is the average lifetime of civilizations.
Fermi Paradox
The Question: If life is common, why haven’t we been contacted by advanced civilizations?
Possible Answers:
Civilizations are rare.
Interstellar travel is too difficult or civilizations self-destruct.
Civilizations exist, but we haven’t met them yet.
