I’d be interested in seeing a similar video presentation on the life cycle of stars, particularly about fusion reactions and the “evolution” of elements through fusion. Also, why does fusion stop at iron? I’ve never really understood that.

I have a question that’s not really related, but is something I’ve wondered for a long time. Maybe somebody here can answer this, or at least point me in the right direction: It’s now fairly commonly accepted that the universe is about 13.7 billion years old (give or take). Are there theories out there addressing the question of what stage of development the universe is at? If we use the analogy of human development, is the universe an infant, toddler, adolescent, adult, middle-age, senior…?

@ 51. Elkin
I read from Lee Smolin’s book, “Life of the Cosmos”, that the distribution of stars in a galaxy are actually fairly uniform. The spiral arms we see have more to do with the age or brightness stars in those regions. The arms are populated by hotter, brighter, younger stars, and the “gaps” are populated by older, dimmer stars and the interstellar medium: gas and dust left over from the explosive death of old stars. The “movement” of the spiral arms don’t correlate directly with the movement of the stars within the arms. Instead, the movement of the spiral arms shows the moving trend of the life and death of the regional stellar community. Young, hot stars are born our of the interstellar medium and over time, burn themselves out or blow themselves up, leaving behind gas and dust, and the cycle repeats itself. Think of “the wave” in a stadium. The wave moves, but the people making the wave don’t move with the wave. Amazing how galaxies work!

Sorry, but AFAIK there is no definite answer yet on why and especially how those monsters grow and become as massive as they are. In fact, this is a current topic of research.
Although the video seems to claim otherwise, it is almost unknown how SMBHs have grown so fast. They accumulated masses of billions of suns in less than a billion years. This is incredibely fast.
Last year I heard a talk about a numerical simulation with self-gravitating accretion disk. The pre-fix is important, because it indicates that the disk is massive enough to be an important part of the gravitational potential, which is negelegted normally. This means that the potential is not influenced by the black hole alone. The simulation gave interesting results: According to them it was possible to give rise to such massive monsters in such a short period of time.

(P.S.: Isn’t it a wonderful thing when physicist talk about scales, espacially time? Ask a partical physicist and he will tell you that 10^-16 seconds are incredibely long – and an astrophysicist will tell you that a few million years are rather short! I love physics! )

Would the “wimpiness” of the Milky Way’s BH be a indication of a relatively smaller amount of material falling into it in the past, and could that be an indication that our galaxy would have had either a comparatively shorter, or significantly less spectacular, period in its past as a quasar or other type of active galaxy?

Great stuff, as always. Thanks, BA!