Far out cosmology: Milky way formation and future (Introduction)

by David Turell , Saturday, January 27, 2024, 16:11 (91 days ago) @ David Turell

Had an early start:

https://bigthink.com/starts-with-a-bang/milky-way-grew-up/?utm_campaign=swab&utm_so...

"The Milky Way galaxy may be just one among trillions present within the observable Universe, but it’s uniquely special for personal reasons to us: it’s our cosmic home. It’s the fertile soil from which our Sun and Solar System, including the bodies that would eventually become planet Earth, sprung some 4.6 billion years ago. All told, it’s composed of a few hundred billion stars, about a trillion solar masses worth of dark matter, a supermassive central black hole of about 4 million solar masses, and a plethora of gas and dust. And that’s no outlier; we’re actually somewhat typical of modern galaxies, with perhaps a hundred billion others similar to our own. We’re neither among the biggest nor the smallest of galaxies, nor are we in an ultra-massive cluster or found in isolation, but rather a modest galaxy group, where we’re the second-largest member.

"Our galaxy today, in other words, is the result of 13.8 billion years of cosmic evolution, where large numbers of small proto-galaxies merged together, forming one larger-than-average galaxy, while continuously attracting additional matter into itself. We are what remains after countless other galaxies have been swallowed by our own.

***

"Galaxies, you see, don’t just grow by attracting other galaxies and merging together to form larger ones. Galaxies also experience evolution on their own, meaning that they:
rotate, form stars, funnel matter in toward the center, generate density waves along their spiral arms, attract additional matter from outside the galaxy along cosmic filaments,
and change shape and orientation based on the other galaxies and matter that falls into them.
While the earliest proto-galaxies that eventually grew into the Milky Way may have formed somewhere around 200-250 million years after the Big Bang, cosmic evolution continued all throughout that time.

***

"In some sense, we already know that our fate is sealed. The Milky Way itself is destined, approximately 4 billion years from now, to begin merging with Andromeda, and then in another 3 billion years, that merger process is expected to reach completion: resulting in a new, larger, single galaxy that already has the rather poetic name of Milkdromeda.

***

"The cosmic story that led to the Milky Way is a story of constant, but not necessarily ultra-violent, evolution. We likely formed from hundreds or even thousands of smaller, early-stage proto-galaxies and early galaxies that merged together. The spiral arms that we see today were likely formed many times by interactions, only to re-form from the rotating, gas-rich nature of an evolving, gas-rich, disk galaxy. Star formation occurred inside in waves, often triggered by minor mergers or gravitational interactions, but also occurring during quiet periods in our galaxy’s life: quiescent star formation. Finally, these waves of star-formation, as stars live-and-die, bring along increases in supernova rates, stellar cataclysms, and heavy metal enrichment of the interstellar medium.

"These changes don’t occur all-at-once and abruptly, but rather in a continuous fashion. They were not just a part of our cosmic past, but are still occurring, and will come to an extremely spectacular conclusion just a few billions of years in the future, as all the galaxies of the Local Group eventually will coalesce and merge together. Every single galaxy has its own unique cosmic story, and the Milky Way is just one typical example of a somewhat mature, larger-than-average but not among the largest galaxies, found within the Universe. What’s important to recognize is that the story hasn’t ended yet. As grown up as we are, the Milky Way, our cosmic home, is still evolving."

Comment: We live in our own home galaxy, quietly observing the vast universe around us. It all evolved from the Big Bang. I prefer to examine any process from the standpoint of purpose. Since we have evolved on Earth and are unique thinking beings, it is reasonable to conclude we were the purpose. Even if other colonies of thoughtful folks exist throughout the universe, the same conclusion applies. From a designing mind creating other minds to join with it is a reasonable conclusion.