(Based loosely on Science, March 19, 1993, p. 1692.)

Stage 0. The Universe is formed in the Big Bang.

Stage 1. Young galaxies form – dust and gas collapsing
gravitationally toward the centre of each.

Stage 2. This triggers the production of very large and short-lived stars (25 times Sun mass, 100 million years life-span) at about the same time, synchronized.

Stage 3. This birth and death of many stars within a short time-period is called STARBURST, and explains the luminosity of many quasars, except the super-bright ones. That is why they are at the outer edge of the Universe; they are very far distant in space because they are very early in time.

Stage 4. At the galaxy centre, a black hole starts forming, and begins to swallow near-by stars as well as dust and gas clouds.

Stage 5. The combination of galactic wind from the Active Galactic Centre (AGN) (i.e. the black hole and the glowing surroundings) and the rotation of the galaxy
forms spiral arms, at first extended rather wide.

Stage 6. Smaller stars (several Sun masses down to one Sun mass) form in the spiral arms under the influence of the galactic wind, which is creating compression waves in the dust and gas clouds.

Stage 7. Some of these Sun-like longer-lived stars (second or third generation stars) develop planetary systems, on some of which life may arise, using the heavier elements created by the first and second wave of supernovae.

Stage 8. As the galaxy rotates faster and faster, the spiral arms curl around tighter and tighter, like a skater in a pirouette. Eventually the arms are absorbed into the disk and the galaxy becomes an ellipse rather than a spiral. The Suns, planets, and life are now dead.

Stage 9. At the same time, the black hole in the AGN grows by accretion until it is millions of Sun masses large. The heat and radiation it emits in further ever-accelerating accretion accounts for the brilliance of the brightest quasars. [But why are THEY far away?]

Stage 10. Eventually (this has not happened yet) all dying galaxies will become super-huge black holes by swallowing all their stars and inter-stellar matter.

Stage 11. Finally, all the billions of dead galaxies will collapse together in the Big Crunch, as the expansion of the Universe slows and reverses.

Stage 12. Then a new Universe will be born in the next Big Bang.