The Interstellar Medium and How Stars Form · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

The gas between stars, and how it becomes stars

Science · Astronomy & Astrophysics · ages 21-22
Name ______________________   Date ____________

  1. Hot thin gas between stars is best observed in which window?

    • Radio waves
    • Visible light
    • X rays

  2. Which of these is the cold dense phase that can collapse into stars?

    • Warm neutral gas
    • Cold molecular clouds
    • Hot thin gas

  3. Dust makes a distant star look redder and fainter than it truly is.

    Circle one:   True   False

  4. Two clouds hold equal mass. One is colder and denser. Which is more likely to collapse?

    • Neither can ever collapse
    • The colder denser one
    • The warmer thinner one

  5. A star's brightness distance without dust correction is 2,000 light years, but dust dims its light. Where is the star?

    • Closer than 2,000 light years
    • Farther than 2,000 light years
    • Exactly at 2,000 light years

  6. A collapsing cloud spins faster as it shrinks. What lets most of its mass still reach the protostar?

    • The cloud stops turning as it shrinks
    • Gravity pauses while the spin fades
    • The excess spin leaves through disks, jets, and magnetic braking

  7. A radio map of a region glows exactly where the X ray map is dark. What does that tell you?

    • Both maps must be broken
    • Cold molecules sit where the radio glows and hot gas sits elsewhere
    • The whole region has one single temperature

  8. A friend studies a very red star and concludes it must be cool, with no dust check. What is the flaw?

    • Reddening by dust can fake a cool look, so dust must be ruled out first
    • Red stars are never found behind dust
    • Dust makes stars look bluer, not redder
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Answer key

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

The gas between stars, and how it becomes stars W1-mt_i2HyLf_Emy-s1

  1. X rays · Each phase owns its window, and hot thin gas shines in X rays.
  2. Cold molecular clouds · Only the coldest densest phase gives way under its own gravity.
  3. True · Dust scatters blue light away, so the star looks redder and dimmer.
  4. The colder denser one · Cooling and crowding hand victory to gravity in the Jeans argument.
  5. Closer than 2,000 light years · Dimming fakes extra distance, so the uncorrected value overshoots.
  6. The excess spin leaves through disks, jets, and magnetic braking · Shedding spin through disks, jets, and braking lets contraction continue.
  7. Cold molecules sit where the radio glows and hot gas sits elsewhere · Different windows light up different phases living in different spots.
  8. Reddening by dust can fake a cool look, so dust must be ruled out first · Dust reddens light, so redness alone cannot prove a star is cool.
Worksheet · LightMySky