June 14, 2020 – Stellar Family Hierarchy

Like in a kinship chart, stars get placed into historical context and this helps us see how the universe progressed from the big bang.

We are star stuff.  Most everything around us is star stuff.  Yet, stars didn’t exist until about 200 million years after the big bang so there was stuff before star stuff.

That stuff was mostly hydrogen and some helium.  They appeared after the dark ages, that time when our universe was seething plasma, a dense goo of sub-atomic particles.  Around 300 thousand years after the big bang the universe cooled just enough for hydrogen and helium to emerge.  Space cleared and well, it was still dark.  Photons existed but not in the human visible range.  They were zipping around as microwaves with nothing to cook.  No stars, just darkness!

This is where we begin, with the first stars.

All this hydrogen in the early universe formed massive molecular clouds. The clouds condensed, rotation started, and the first stars popped into existence.  Let there be light!  Helium isn’t known to form stars but was there along with hydrogen.  The first stars were unlike most stars today.  Many were super massive, blue-white, super-hot, and burned through hydrogen so fast they just blew apart after a few million years.  This was the beginning, the beginning of everything star stuff.  These earliest, first generation of stars are termed population III stars, and none have been definitively found.  While not surprising since most were short-lived, there should have been smaller, long-lived stars born as first-generation stars.  The search is on.

Those first stars seeded the early universe with heavier elements.  How?  Fusion is how stars work. Hydrogen fused into helium, then helium into carbon.  Subsequent violent core collapses and ultra-nova explosions spewed the elements carbon, oxygen, and metals like lithium.  Most probably blew apart but some survived as monster black holes.  Now our universe had some other star stuff, elements heavier than hydrogen and helium.

As these population III stars were growing and exploding, the next generation of stars was forming in molecular clouds.  The new stars formed with a compliment of heavier elements from exploded population III stars. Astrophysicists classify these younger stars population II stars. Population II stars are still old, some as old as 13 billion years, and most reside in globular clusters or around the Milky Way’s bulge.

Our Sun is a population I star, about 5 billion years old, with 10 times the heavier elements as population II stars.  This “element seeding” process will continue, and new stars will have more and more metals and other heavier elements.  But at some point, maybe a trillion years from now, hydrogen will be too sparse to fuse and form a star.

Will that be the beginning of the end?

What’s in the Sky?

June 19; 30 minutes before sunrise; east-northeast: A crescent Moon and crescent Venus will be less that one degree apart.