Star Formation and Nuclear Fusion

• Stars = massive collections of hydrogen atoms collapsed from gas clouds under gravity
• Core nuclear fusion crushes hydrogen → helium, releases tremendous energy
• Radiation pushes against gravity, maintaining delicate balance
• Fusion in core = star remains stable
• Massive stars (way more mass than Sun) can fuse heavier elements until iron

Stellar Death and Black Hole Formation

• Iron fusion doesn't generate energy, builds up at star center
• Critical mount reached → balance between radiation/gravity broken
• Core collapses within fraction of second
• Star implodes at ~1/4 speed of light, feeding more mass into core
• All heavier elements created as star dies in supernova explosion
• Results: neutron star OR (if massive enough) entire core mass collapses into black hole

Black Hole Structure and Properties

• What you see = Event Horizon (black sphere reflecting nothing)
• Anything crossing Event Horizon needs >speed of light to escape = impossible
• The Singularity = "hole part" of black hole
  • May be infinitely dense (all mass concentrated in single point)
  • No surface or volume
  • Could be something completely different
  • Currently unknown ("dividing by zero error")
• Black holes don't suck like vacuum cleaner
• Swapping Sun for equally massive black hole = Earth unchanged (except freezing)

Falling Into Black Hole Experience

• Time experience different around black holes
• From outside observer: you slow down approaching Event Horizon
  • Time passes slower for you
  • Eventually appear to freeze in time
  • Slowly turn red and disappear
• From your perspective: watch rest of universe in fast forward (seeing into future)

Death Scenarios Inside Black Hole

Scenario 1: Spaghettification

• Black hole curves space so much that only one possible direction after crossing Event Horizon
• Like tight alley closing behind you after each step
• Mass so concentrated = gravity acts with millions times more force on different body parts
• Cells torn apart, body stretches until hot stream of plasma one atom wide

Scenario 2: Firewall Death

• Very soon after crossing Event Horizon = hit firewall
• Terminated instantly
• Death timing depends on black hole mass
  • Smaller black hole kills before entering Event Horizon
  • Super massive black hole = could travel inside quite a while
• Rule of thumb: further from singularity = longer you live

Black Hole Size Classifications

Stellar Mass Black Holes

• Few times mass of Sun
• Diameter of asteroid

Super Massive Black Holes

• Found at heart of every galaxy
• Feeding for billions of years
• Largest known: S514+81
  • 40 billion times mass of Sun
  • 236,000 billion km diameter
  • 47 times distance Sun to Pluto

Hawking Radiation and Evaporation

• Black holes eventually evaporate through Hawking radiation
• Empty space filled with virtual particles popping into existence/annihilating
• At black hole edge: one virtual particle drawn in, other escapes as real particle
• Black hole loses energy incredibly slowly at first, faster as becomes smaller
• Mass of large asteroid = radiating at room temperature
• Mass of mountain = radiates with heat of Sun
• Last second of life = radiates energy of billions of nuclear bombs in huge explosion
• Biggest black holes take up to googol years to evaporate
• When last black hole radiates away = universe uninhabitable long before then

Future Content

• More interesting black hole ideas to explore in part two
• Acknowledgment to Fraser Kane for video help
• Kurzgesagt wallpapers available in 4K on Patreon