Ask Ethan: How many generations of stars came before the Sun?

"molecular gas clouds that are contracting and fragmenting, leading to protostars and young stellar objects, becoming full-fledged stars with protoplanetary disks around them, conventional stars burning through their fuel with their own fully-formed planetary systems, stars evolving into subgiants, giants, and even supergiants, stars dying in planetary nebulae, supernovae, and other life-ending events, and stellar remnants of now-extinct stars like white dwarfs, neutron stars, and black holes."

"It was a full 9.2 billion years after the hot Big Bang first began, or roughly 4.6 billion years ago, that our Sun and Solar System began forming in our own Milky Way: some 27,000 light-years from the galactic center. And now, all this time later, human beings have risen to prominence here on planet Earth, having reconstructed our cosmic history more successfully than ever before."

Stars in the Milky Way occupy every stage of stellar life, from contracting molecular clouds to protostars, full stars with protoplanetary disks, mature stars with planetary systems, evolved giants and supergiants, explosive deaths, and compact remnants. Cosmic history can be traced 13.8 billion years back to the hot Big Bang, with star-formation rates inferred across that span. The Sun and Solar System began forming about 4.6 billion years ago, roughly 9.2 billion years after the Big Bang, at about 27,000 light-years from the galactic center. Determining how many stellar cycles preceded the Sun requires detailed investigation of galactic chemical enrichment and stellar lifecycles.

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