Everything Everywhere Daily: History, Science, Geography & More - Galaxies

Starting point is 00:00:00 For most of human existence, we looked up at the night sky and thought that that's all there was to the universe. However, in the 20th century, as telescopes improved, we made a shocking discovery. The universe was much, much larger than we suspected. And many of those points of light in the sky were, in fact, collections of stars themselves. Learn more about galaxies, what they're made of, and all about our own, on this episode of Everything Everywhere Daily. Do you ever climb into bed ready to sleep, only to have your mind, start racing the moment your head hits the pillow? Thoughts bouncing around, replaying the day, or jumping ahead to tomorrow? That is exactly why Catherine Nikolai created Nothing Much Happens. Each episode is a

Starting point is 00:00:53 gentle, cozy bedtime story where, well, nothing much happens. No drama, no tension, nothing you need to follow closely. Just soft narration, calming repetition, and soothing sensory details designed to help your mind slow down and your body relax. It's not about entertainment, it's about rest. And millions of listeners around the world use it every night to quiet their thoughts and finally fall asleep. If you've ever struggled to shut your brain off at night, this might be exactly what you've been missing. You can listen to Nothing Much Happens wherever you get your podcasts. Episodes are every Monday and Thursday. If we wanted to provide a very rough taxonomy of the universe, we could start with things like planets, planetoids, asteroids, meteors, and other such bodies.

Starting point is 00:01:40 These are usually rocky objects or can sometimes be amalgamations of gas like Jupiter. All of these objects are objects whose matter is gravitationally, or in the case of very small objects, chemically or electrostatically, bound to itself. Then you have stars, which I've talked about in a previous episode. Most planets and planet-like objects that we know of are under the gravitational influence of a star. They orbit around it and are part of a star's solar system. A star, of course, is simply an amalgamation of gases, usually hydrogen and helium, that is massive enough for fusion to occur. For the longest time, this is what we assumed the universe consisted of. We had objects in our solar system of which we were aware, and then there were other stars in the sky that we could see.

Starting point is 00:02:27 However, there was something else in the sky that weren't points of light. There was a band of faint light that could be seen in the sky. It didn't extend over the entire sky. It was as if it was a faint smear of light which extended across it. We know this band of faint light as the Milky Way. Over the centuries there were theories as to what this smear of light was. The Greek philosopher Democritus, as early as the 5th century BC, thought that it was a collection of very distant stars. The Arab astronomer Al-Hazin in the 10th century tried to measure the parallax of the Milky Way and realized there was no parallax.

Starting point is 00:03:04 Parallax is the change of apparent position of an object related to more distant objects caused by a change in the observer's line of sight towards the object. So a star will be in a slightly different position when the Earth is on one side of the sun than it will be when the Earth is on the other side six months later. And you can observe parallax for very close objects by looking at nearby things with one eye closed and then the other. Because the Milky Way had no measurable parallax, it meant that it must have been very, very far away. In the early 17th century, Galileo first looked at the Milky Way through a telescope and found that it did, in fact, consist of a great many faint stars.

Starting point is 00:03:43 One of the biggest insights as to what the Milky Way was was made by the English astronomer Thomas Wright in 1750. In a book titled, An Original Theory or New Hypothesis of the Universe, he theorized that the Milky Way was a collection of stars that was gravitationally held together. There were other questions that arose as telescopes became better. Not all of the lights in the sky were stars. Some of them were known as nebulae. There were different types of nebula. Some appeared to be clouds and other appeared to be spirals.

Starting point is 00:04:14 These spiral nebulae were actually very perplexing. The aforementioned Thomas Wright proposed that some of these nebula were, were in fact, separate Milky Ways. What exactly the spiral nebulae were became one of the most hotly contested controversies in astronomy in the early 20th century. It all came to a head on April 26, 1920, when the two proponents for each side of the debate presented their cases at the Smithsonian Museum of Natural History. This became known as the Great Debate. At stake was nothing less than the size of the universe. On one side of the debate was Harlow Shapley, head of the Harvard Observatory. He contended that spiral nebulae, such as the Andromeda Nebula, were part of the same system as all the other

Starting point is 00:04:57 stars that we could see. On the other side was Herbert Curtis, the director of the Allegheny Observatory. He contended that the spiral nebulae were in fact completely separate systems of stars located outside of our own and vastly further away. Curtis came to this conclusion after observing ten different novas take place within the Andromeda nebula, all of which were an order of magnitude fainter than those otherwise observed in the sky. No one walked away a winner from the debate that evening, but over time the evidence accumulated, and Curtis was right.

Starting point is 00:05:30 Andromeda and other spiral nebula were in fact separate collections of stars, vastly further away from the individual stars that we can see in the sky. At first, they were called island universes, but that was sort of awkward, so they were eventually just called galaxies. Thomas Wright's theories from way back in the 18th century were also generally proven correct. The Milky Way that we see in the sky is our galaxy, and it's a flat disk of stars that we can see from the edge. As astronomical observations improved, more and more galaxies were discovered. And there wasn't just one type of galaxy. There were, in fact, a variety of galactic types. Edwin Hubble, the astronomer who ended the great debate by measuring the distance to several spiral nebulae,

Starting point is 00:06:17 categorized the various types of galaxies. There were spiral galaxies with different shapes and types of arms, and there were elliptical galaxies which were mostly smooth without arms, and there are irregular galaxies without form. and it actually goes into far more detail than that, but those are roughly the types. So, after a century of discovering the existence of galaxies, what have astronomers learned about them? For starters, the size of a galaxy can vary dramatically. A dwarf galaxy can consist of as little as a few thousand stars up to a billion stars. Most galaxies, such as our own, consists of

Starting point is 00:06:51 100 to 400 billion stars. The largest galaxies known as super-giant ellipticals may consist of trillions of stars and were likely created by swallowing up other galaxies. The closest galaxy to the Milky Way might be the Canis Major Dwarf Galaxy. It's approximately 25,000 light years away from Earth, and I say maybe because some speculate that it isn't in fact a separate galaxy at all, but actually a part of the Milky Way. The large and small Magellanic clouds are located about 160,000 and 200,000 light years away. As with the Canis Major Dwarf galaxy, both the Magellanic clouds are gravitationally bound to the Milky Way, so they're sort of like satellite galaxies. The closest galaxy which is not gravitationally bound to the Milky Way is the Andromeda galaxy.

Starting point is 00:07:40 It's located about 2.5 million light years away from us in the constellation of Andromeda. In fact, Andromeda is on course to collide with the Milky Way in about 4.5 billion years. Galactic collisions are not the violent events that they might sound like. It is entirely possible for galaxies to collide but for no stars to actually touch. It's more a matter of gravitational influence, not physical collision. The Milky Way has a diameter of about 100,000 light years, and it's a spiral galaxy. Our solar system is located about midway on one of the spiral arms, about 25,000 light years from the galactic core. It takes the sun about 250 million years, to complete an orbit around the center of the galaxy. And this period of time is known as a galactic year or a cosmic year. Our galaxy, like most galaxies, has a supermassive black hole in its center, something which I covered in the episode on black holes. These are the gravitational sources of gravity that bind objects in the galaxy together.

Starting point is 00:08:43 The number of galaxies in the universe is an estimate which keeps getting updated as more and better observations are made. Telescopes like the James Webb are now able to peer back about as far as possible. One of the observations which demonstrated the mind-boggling number of galaxies in the universe was the Hubble Deep Field image. 10% of the Hubble Space Telescope's observation time is devoted to what is known as Director's Discretion.

Starting point is 00:09:09 In 1995, the then-director of the Space Telescope Science Institute, Robert Williams, decided to point the Hubble towards a relatively empty patch of sky that was 1.24 millionth the area of the total sky. Over a period of 10 days and hundreds of exposures, the result was an image that changed astronomy. This tiny empty patch of sky was filled with galaxies. Subsequent deep-filled images have shown the same thing no matter where they point the camera. So while we know that there are a lot of galaxies, the total number is kind of a wild estimate because we can't see most of the universe.

Starting point is 00:09:46 The current best guess is that there are between a hundred billion to a trillion, million galaxies in the universe. But don't be surprised if that estimate is updated in the future. Galaxies aren't the end of when it comes to structures in the universe. Galaxies themselves can be bound together to form galactic clusters. There may be hundreds to thousands of galaxies in a galactic cluster. Even large clusters known as superclusters may have tens of thousands of galaxies in them. These clusters are shaped into sheets and filaments with enormous voids between them with no galaxies. The Hercules Corona Borealis Great Wall is the largest structure in the universe. It's 10 billion light years long and 7 billion light years wide. And to put that into perspective,

Starting point is 00:10:33 the total observable universe is only 93 billion light years in diameter. It consists of many tens of thousands of galaxies, each of which may contain hundreds of billions to trillions of stars. And unlike the Great Wall in China, this Great Wall can be seen from space. In some ways, galaxies, not stars, can be thought of as the fundamental units of the universe, at least if you take a big enough perspective. Not only are their sizes awe-inspiring and mind-bending, but just one century ago, nobody was even sure if they existed. Today we know that our galaxy isn't alone, but there may be hundreds of billions to trillions of others out there, similar to ours.

Starting point is 00:11:18 The executive producer of Everything Everywhere Daily is Charles Daniel. The associate producers are Thor Thompson and Peter Bennett. Today's review comes from listener B-Rage 42 over on Apple Podcasts in Norway. They write, This is the best podcast ever. Talkskolduha, Be-Rage. You'll be happy to know that your review is the first one ever from Norway. And with it, we have now unlocked the Norwegian badge.

Starting point is 00:11:43 Construction of the Norway Completionist Club is now underway. And I know I have people listening from all over the world. if you would like to unlock your country, just leave a review. There are still several large countries, including Austria, Switzerland, Japan, the Philippines, France, and South Africa, where I know I have people listening, but I have yet to get a review. And if you would like to leave a review or send me a boostogram from anywhere in the world, you two can have it read on the show.

Everything Everywhere Daily: History, Science, Geography & More - Galaxies

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