We live in a galaxy called the Milky Way. An empire with hundreds of billions of stars. There are two hundred billion galaxies in the known universe. Each one unique, enormous and dynamic. How the Universe Works s1e3: Galaxies
The stars in a galaxy are born in clouds of dust and gas called nebulas. ibid.
Our galaxy contains many billions of stars. And around many of them are systems of planets and moons. But for a long time we didn’t know much about galaxies. Just a century ago we thought the Milky Way was all there was. Scientists called it our island universe. For them no other galaxies existed. Then in 1924 astronomer Edwin Hubble changed that thinking. ibid.
Galaxies are big. Really really big. ibid.
Andromeda our nearest galactic neighbour is over two-hundred thousand light years across. Twice the size of our galaxy. ibid.
They all seem to orbit something at their centre ... A black hole. And not just any sort of black hole: but a supermassive black hole. The meal is gas and stars. And it’s being consumed by the supermassive black hole. But sometimes black holes devour too quickly. And what they’re consuming is discharged back into space as beams of pure energy. It’s called a Quasar. ibid.
When scientists see a quasar blasting from a galaxy they know it has a supermassive black hole. ibid.
A maverick scientist came up with the idea that something else was at work. Back in the 1930s Swiss astronomer Fritz Zwicky wondered why galaxies stayed together in groups. ibid.
It’s clear now that Dark Matter is a vital ingredient of the universe. It’s been working since the dawn of time. And affects everything, everywhere. It triggers the birth of galaxies. And stops them from falling apart. We can’t see it or detect it. Nevertheless, Dark Matter is the master of the universe. ibid.
Each of the filaments is home to millions of galaxy clusters. All bound together by Dark Matter. ibid.
Dark Matter holds together the whole super-structure of the universe. It binds galaxies in clusters. And clusters in super-clusters. All these are locked together in a web of filaments. Without Dark Matter the whole structure of the universe would simply fall apart ... It’s a giant cosmic web. ibid.
Dark Energy has the opposite effect of Dark Matter. Instead of binding galaxies together it pushes them apart. ibid.
On the international space-station astronaut Don Pettit was experimenting in zero gravity. He put grains of salt and sugar inside a plastic bag, and instead of floating apart they began to clump together. This is how planets and moons build up. How the Universe Works s1e8: Moons
Our universe is at war. Entire galaxies fight to the death. Only the strongest survive. Our own galaxy also fights for survival. These battles are how galaxies live, grow and die. How the Universe Works s9e1: When Galaxies Fight
Inflation explains why galaxies are spread so smoothly across the cosmos. How the Universe Works s3e4: First Second of the Big Bang
Looking up and out, how can we not respect this ever-vigilant cognizance that distinguishes us: the capability to envision, to dream, and to invent? The ability to ponder ourselves? And be aware of our existence on the outer arm of a spiral galaxy in an immeasurable ocean of stars? Cognizance is our crest. Vanna Bonta
I think that the event which, more than anything else, led me to the search for ways of making more powerful radio telescopes, was the recognition, in 1952, that the intense source in the constellation of Cygnus was a distant galaxy – 1000 million light years away. This discovery showed that some galaxies were capable of producing radio emission about a million times more intense than that from our own Galaxy or the Andromeda nebula, and the mechanisms responsible were quite unknown ... Possibilities were so exciting even in 1952 that my colleagues and I set about the task of designing instruments capable of extending the observations to weaker and weaker sources, and of exploring their internal structure. Martin Ryle
Are we a lone island of life lost in a vast galaxy? Brian Cox, Human Universe III: Are We Alone? BBC 2014
Red Dwarfs are by far the most numerous stars in our galaxy. ibid.
There are ten billion inhabitable worlds out there in the Milky Way Galaxy. ibid.
Our galaxy is falling towards other galaxies in the universe. ibid.
There are at least as many galaxies in our observable universe as there are stars in our galaxy. Martin Rees
Far out in the uncharted backwaters of the unfashionable end of the western spiral arm of the Galaxy lies a small unregarded yellow sun. Orbiting this at a distance of roughly ninety-two million miles is an utterly insignificant little blue green planet whose ape-descended life forms are so amazingly primitive that they still think digital watches are a pretty neat idea. Douglas Adams, The Hitchhiker’s Guide to the Galaxy