Hydrostatic Equilibrium and the Structure of a Star · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

What holds a star up

Science · Astronomy & Astrophysics · ages 20-21
Name ______________________   Date ____________

  1. Why must temperature rise toward the star's center?

    • Deeper layers carry more weight, needing more pressure
    • The surface radiates heat inward
    • Heavy elements sink and ignite there

  2. What balances gravity inside a steady star?

    • Centrifugal spin of the core
    • Magnetic fields of the corona
    • Outward gas and radiation pressure

  3. A star's center is its hottest part.

    Circle one:   True   False

  4. Why are massive stars far more luminous?

    • They hold more unburned fuel
    • They spin much faster
    • Greater weight needs fiercer central burning

  5. A star's core squeezes slightly. What follows?

    • It cools until fusion stops
    • It heats, fusion quickens, pressure pushes back out
    • It collapses with no resistance

  6. Type the Sun's central temperature in millions of kelvin.

    Answer: ______________

  7. What sets the pressure at the Sun's center?

    • The spin rate of the core
    • The piled-up weight of all layers above
    • The strength of sunspots

  8. A student says pressure pushes inward to hold the star. What is wrong?

    • Pressure pushes outward; gravity pulls inward
    • Stars contain no pressure at all
    • Gravity pushes outward instead
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Answer key

For grown-ups. Fold this page away before handing over the rest.

What holds a star up W1-mt_RKeMW8iX56-s1

  1. Deeper layers carry more weight, needing more pressure · More overlying weight needs more pressure, which needs more heat.
  2. Outward gas and radiation pressure · Rising pressure pushes out exactly as hard as gravity pulls in.
  3. True · Temperature climbs inward so heat flows outward, peaking at the center.
  4. Greater weight needs fiercer central burning · Heavier stars must burn harder to support themselves, so they radiate more.
  5. It heats, fusion quickens, pressure pushes back out · The star acts as a thermostat: squeeze raises heat, which restores the push.
  6. 15 · Balance against collapse demands about 15 million kelvin at the center.
  7. The piled-up weight of all layers above · Central pressure is the cumulative weight of every overlying shell.
  8. Pressure pushes outward; gravity pulls inward · The directions are swapped: gravity pulls in, pressure pushes out.
Worksheet · LightMySky