Dark Matter, Dark Energy and What the Universe Is Made Of · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

The universe we cannot see

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

  1. How much extra mass do galaxy clusters need to stay together?

    • Exactly what we see
    • Five to ten times more than we see
    • Half of what we see

  2. What does a flat rotation curve say about a spiral galaxy?

    • Only its visible stars supply the gravity
    • Unseen mass surrounds it in a vast halo
    • It has no gravity at all

  3. Gravitational lensing maps agree with the galaxy motion evidence.

    Circle one:   True   False

  4. About what share of the critical density is ordinary matter?

    • About half of it
    • About a quarter of it
    • About 5 percent of it

  5. Distant supernovae look dimmer than their redshifts allow. What does that mean?

    • The supernovae are unusually faint
    • The universe is contracting
    • The expansion is speeding up

  6. Dark energy supplies about what percent of the critical density?

    Answer: ______________

  7. A student says dark energy must be slowing the expansion. What is wrong?

    • Dark energy does not affect expansion at all
    • The supernova distances show speeding up, not slowing
    • Supernovae cannot measure distance

  8. A student blames flat rotation curves on dim stars and planets. What is wrong?

    • Dim objects would still be ordinary matter, capped near 5 percent
    • Dim objects have no gravity
    • Rotation curves never stay flat
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Answer key

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

The universe we cannot see W1-mt_GKKPGcHqJH-s1

  1. Five to ten times more than we see · Member galaxies move too fast for visible gravity alone.
  2. Unseen mass surrounds it in a vast halo · Speeds should fall off, but they stay high far out.
  3. True · Both point to the same extra unseen mass.
  4. About 5 percent of it · Familiar matter is only a small slice of the total.
  5. The expansion is speeding up · Extra distance means extra expansion since the light left.
  6. 68 · Dark energy is the largest share at about 68 percent.
  7. The supernova distances show speeding up, not slowing · Dimmer than expected means pushed farther by acceleration.
  8. Dim objects would still be ordinary matter, capped near 5 percent · Hidden ordinary matter cannot reach the needed 27 percent.
Worksheet · LightMySky