Galaxy Types, the Milky Way's Structure and Active Nuclei · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Sorting galaxies and weighing their bright hearts

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

  1. Where do the youngest hottest stars live in a spiral galaxy?

    • In the sparse outer halo
    • In the old central bulge
    • In the disc and arms where the gas sits

  2. A galaxy shows a flat blue disc with arms plus a yellow central bulge. What type is it?

    • Spiral
    • Elliptical
    • Irregular

  3. Elliptical galaxies hold plenty of gas and keep forming many new stars.

    Circle one:   True   False

  4. A smooth round galaxy glows yellow with almost no gas. What is its star forming future?

    • It will keep forming bright blue stars for billions of years
    • It will soon collide and always turn irregular
    • It will mostly fade as its ageing stars grow old

  5. An astronomer inside the disc wants to trace the spiral arms. Which toolkit works through the dust?

    • Visible light photos alone
    • Radio maps of gas plus infrared star counts
    • Counting only the nearest bright stars by eye

  6. A galactic centre outshines all its stars and flickers within days. What powers it?

    • A dense cluster of ordinary young stars
    • Gas spiralling into a supermassive black hole
    • Millions of supernovae exploding at once

  7. Spiral arms stay bright blue because the same stars sit in the arms forever while gas flows past them.

    Circle one:   True   False

  8. A student says a quasar must be billions of separate stars because it is so bright. What defeats that claim?

    • Its brightness changes within days, so the source is light days wide
    • Quasars are always found outside galaxies
    • Stars never produce any light at all
LightMySky · lightmysky.comW1-mt_Eps5CXEB5C-s1

Answer key

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

Sorting galaxies and weighing their bright hearts W1-mt_Eps5CXEB5C-s1

  1. In the disc and arms where the gas sits · New stars are born from gas, and the gas lives in the disc and arms.
  2. Spiral · Blue armed discs with a yellow bulge are the spiral signature.
  3. False · Ellipticals burned through their gas long ago and glow with ageing stars.
  4. It will mostly fade as its ageing stars grow old · Without gas there is no fuel, so an elliptical simply ages.
  5. Radio maps of gas plus infrared star counts · Radio and infrared pass through dust that blocks visible light.
  6. Gas spiralling into a supermassive black hole · Only accretion onto a black hole packs that much power into light days.
  7. False · Stars drift through the arms while the pattern keeps squeezing fresh gas into new stars.
  8. Its brightness changes within days, so the source is light days wide · Fast variation caps the size, and no star crowd fits that cap.
Worksheet · LightMySky