P16 Space Flashcards
How is a star born?
Nebula Collapse:
A giant molecular cloud (nebula) of gas/dust collapses under gravity.
Protostar Formation:
Dense core forms → heats up as gravity compresses it (not yet a star).
Fusion Ignition:
Core reaches 10 million K → Hydrogen fusion begins (now a main-sequence star).
Key Conditions:
Requires sufficient mass (>0.08 solar masses).
Balance: Gravity (inward) vs. Radiation pressure (outward).
How is the solar system formed?
A giant rotating cloud of gas/dust (nebula) collapsed under gravity.
Protostar Formation:
99% of material collapsed into the center → formed the Sun (fusion began at ~10 million K).
Protoplanetary Disk:
Remaining 1% flattened into a disk around the Sun.
Dust grains clumped → planetesimals → protoplanets.
Planet Formation:
Rocky planets (Mercury, Venus, Earth, Mars): Formed near Sun (high temps vaporized volatiles).
Gas giants (Jupiter, Saturn): Formed beyond frost line (icy/rocky cores captured H/He).
Ice giants (Uranus, Neptune): Formed later from remaining icy material.
Why doesn’t the Sun collapse or explode?
Two forces act on the Sun. One is the inward gravitational pressure of the Sun’s mass. The other is the outward pressure from heat generated in its interior. The Sun remains stable because these two forces are in gravitational equilibrium.
How do massive stars (>8x Sun) end their lives?
Red Supergiant:
Swells, fuses elements up to iron.
Supernova:
Core collapses → cataclysmic explosion
Remnant:
Neutron star (ultra-dense) or black hole (if core >3 solar masses).
How do supernovae create heavy elements?
Extreme pressure/temperature during collapse fuses small nuclei → heavy nuclei (e.g., iron → gold).
Explosion scatters these elements into space → forms new stars/planets.
Compare white dwarfs, neutron stars, and black holes.
White Dwarf:
Sun-sized star’s core.
Density: 1 ton/cm³!
Neutron Star:
Supernova remnant.
Density: 1 Mount Everest in a sugar cube!
Black Hole:
Infinite density (escape velocity > speed of light).
What defines a main-sequence star?
Stable phase (like our Sun) fusing hydrogen → helium in its core.
Size/Color Depends on Mass:
Red Dwarfs (tiny, cool, longest-lived).
Yellow Dwarfs (Sun-like, ~10 billion-year lifespan).
Blue Giants (massive, hot, short-lived).
What’s left after a Sun-like star dies?
Earth-sized stellar corpse (no fusion).
Extremely dense (1 ton/cm³!).
Cools over trillions of years → black dwarf (none exist yet).
What happens when stars leave the main sequence?
Red Giant (Sun-like stars):
Swells after hydrogen runs out; fuses helium → carbon.
Red Supergiant (massive stars):
Swells further; fuses elements up to iron (e.g., Betelgeuse).
Fate: Giants → White dwarfs; Supergiants → Supernovae.
What force keeps planets and satellites in orbit?
Gravity acts as the centripetal force, pulling objects toward the center (e.g., Sun → planet, Earth → satellite).
Direction: Always inward, perpendicular to velocity.
Result: Circular/elliptical orbit with constant speed but changing velocity (direction).
Why doesn’t a planet’s speed change in a circular orbit?
Gravity’s force is perpendicular to motion → no work done → kinetic energy (and speed) stays constant.
Acceleration: Directed inward (changes velocity’s direction, not magnitude).
How does orbital speed depend on distance?
Farther orbit → Slower speed (weaker gravity).
Farther orbit → Longer orbital period (bigger circumference ÷ slower speed).
What happens if a satellite’s speed changes?
Too slow: Falls to Earth (e.g., atmospheric drag decays orbits).
Too fast: Escapes into space.
Just right: Stable circular orbit (balancing gravity and inertia).
How does firing engines affect a satellite’s orbit?
Speed ↑: Moves to higher orbit (slower speed due to weaker gravity).
Speed ↓: Drops to lower orbit (faster speed).
Why is gravity called a “center-seeking” force in orbits?
Provides centripetal acceleration toward the center.
Without it: Objects move in straight lines (Newton’s 1st law).
How can we tell if a star/galaxy is moving toward or away from Earth?
Redshift: Light waves are stretched (longer λ) → object is moving away.
Blueshift: Light waves are compressed (shorter λ) → object is moving toward us.
What did Edwin Hubble discover about galaxies?
All distant galaxies show redshift → moving away from Earth.
Greater distance = greater redshift = faster recession speed.
Conclusion: The universe is expanding (not centered on Earth!).
Why does redshift imply universe expansion?
No special center: All galaxies move away from each other (like raisins in rising bread dough).
Hubble’s Law: Recession speed (v) = Hubble constant (H₀) × distance (d).
Evidence: Cosmic microwave background (CMB).
How is redshift used today?
Measure distances to galaxies (Hubble’s Law).
Study dark energy (accelerating expansion).
Detect exoplanets (tiny stellar wobbles cause blueshift/redshift).
All Key Stellar Objects & Definitions
Protostar
Newborn star forming from collapsing gas; no fusion yet.
Main Sequence Star
Stable star (e.g., Sun) fusing H → He in core.
Types: Red dwarfs (small/cool), Yellow dwarfs (Sun-like), Blue giants (massive/hot).
Red Giant/Supergiant
Swells post-main-sequence; fuses heavier elements (He → C, Fe).
White Dwarf
Dead core of Sun-like stars; Earth-sized, dense (~1 ton/cm³).
Neutron Star
Supernova remnant; city-sized, ultra-dense (neutrons only).
Pulsar: Spinning neutron star emitting radio beams.
Black Hole
Core >3 solar masses collapses; gravity traps light (event horizon).
Brown Dwarf
“Failed star” (<0.08 solar masses); no sustained fusion.
Quasar
Active supermassive black hole; high redshift reveals early universe.
Supernova
Massive star’s explosive death; creates heavy elements (Fe, Au).
What are galaxies and nebulae?
Galaxies
Definition: Massive gravitationally-bound systems of stars, gas, dust, and dark matter.
Types:
Spiral (e.g., Milky Way) – Rotating disks with arms.
Elliptical – Round/oval; old stars, little gas.
Irregular – No defined shape; often young/starbursting.
Key Fact: Contain billions of stars and often a supermassive black hole at the center.
Nebulae
Definition: Giant clouds of gas (H/He) and dust in space.
Types:
Emission (e.g., Orion Nebula) – Glows from star formation.
Reflection – Dust reflects starlight (blue hue).
Dark – Blocks light (e.g., Horsehead Nebula).
Planetary – Expelled layers of dying stars (e.g., Ring Nebula).
Key Fact: Nebulae are stellar “nurseries” or “graveyards.”
What does the Big Bang theory explain?
The universe began as an infinitely hot/dense point ~13.8B years ago.
Evidence:
Cosmic Microwave Background (CMB) radiation.
Redshift of distant galaxies (Hubble’s Law).
What is the CMB?
“Echo” of the Big Bang: stretched gamma rays → microwaves.
Temperature: ~2.7 K (-270°C), uniform in all directions.
Key proof of universe’s hot, dense origin.
Why do we think dark matter exists?
Galaxies rotate too fast for visible mass alone.
Effects:
Holds galaxies/clusters together.
Increases universe’s density (~27% of total mass-energy).
Cannot be seen (only detected via gravity).
Three possible futures for the universe?
Big Freeze (if dark energy wins): Expand forever → cold, dark.
Big Crunch (if matter wins): Collapse back into singularity.
Big Rip (if dark energy intensifies): Tear apart atoms.
What are WIMPs in astrophysics?
Definition: Hypothetical particles proposed as dark matter candidates.
Properties:
Massive (10–1000x proton mass).
Weakly interacting (ignore EM/strong forces; only gravity/weak nuclear force).
