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Delve into the mysteries of our galaxy and beyond as we uncover why the center of the Milky Way shines so brightly and how the universe rings like a bell. Join us on an awe-inspiring journey through space as we discover other mesmerizing facts about the cosmos.
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00:00Is there a giant mega sun in the center of our Milky Way?
00:04Scientists actually thought so for a while because it's the brightest place in the galaxy.
00:09It has millions of stars packed into a small area.
00:12This area is called the Gigantic Bulge.
00:17The Gigantic Bulge has millions more stars per light year than any other part of the galaxy.
00:23It can be 10 million times denser than our part of the neighborhood.
00:26In some cases, stars in this region are only 5 light days apart.
00:32That's like if there was another star in our solar system a bit further away than Pluto on a space
00:37scale.
00:38But why is this place so dense?
00:41When galaxies form, a lot of gas and dust come together under the force of gravity.
00:46This material gathers up and eventually forms stars.
00:49Gravity and angular momentum balance out and it starts looking like a flat disk with a pretty bright, bulging, dense
00:57core.
00:58The stars live their comfy lives and once they get to the finishing line, they collapse under their own huge
01:04weight.
01:05Then, the black hole forms.
01:08Black holes love to eat everything around them and the more they eat, the bigger they get.
01:13And what place is more perfect for a fine dinner than the galaxy center, where all the space stuff is
01:19packed together?
01:20So, it starts eating surrounding gas and dust, forming an accretion disk.
01:25As this material spirals into the black hole, it heats up and emits a lot of energy, which makes the
01:32center of the galaxy even brighter.
01:34That's why you can find both supermassive black holes and galactic bulges in the centers of all galaxies.
01:43The galactic bulge at the center of the Milky Way looks a bit like an ellipse.
01:48That's a classical bulge.
01:50Stars aren't like our sun.
01:52They move randomly in all possible directions and planes.
01:56Plus, they all move at different speeds.
01:58So, gravity is going crazy there and this makes the bulge look more like a sphere, or an ellipse.
02:05Since they were the first ones to form, they have some of the most ancient stars in our galaxy.
02:11But there are also some places of star formations and lots of younger, massive stars that are less than 100
02:18million years old.
02:20As we move farther away from the center, things get a bit calmer.
02:24Stars start rotating uniformly and become stable.
02:27Right now, Earth is in one of the Milky Way's spiral arms called the Orion Arm, pretty far away from
02:34the galactic bulge.
02:36In our part of the neighborhood, stars are usually about 4 or 5 light years apart.
02:41This means that most of a galaxy is actually just black, empty space.
02:47Our black hole is called Sagittarius A star.
02:50It's a monster about 4 million times the mass of our sun.
02:54It's also about 32 million miles in size, almost like the distance between Mercury and the sun.
03:01But don't worry, it's not attracting the Milky Way inside it, and it's not going to eat us.
03:06These black holes are actually super small compared to the entire galaxy, so they can only eat whatever's around.
03:13Right now, many stars orbit Sagittarius A star.
03:17And even though it emits a huge amount of energy, we can't see its light from Earth without a lot
03:23of scientific effort.
03:26But why don't we see the center itself?
03:28The galactic bulge is so bright that even though it's 26,000 light years away, we should see it shining
03:35brightly in our sky.
03:36Yet, we don't.
03:38Turns out it's all because of space dust.
03:41There's a lot of dust between us and the core, and it absorbs most of the visible light.
03:47We can only look at the galactic core using other types of light, like near-infrared, gamma-ray, and so
03:53on.
03:54NASA has images of the core in different types of light, and it shows how scarily bright the center is
04:00without the dust blocking our view.
04:03But not all bright regions are blocked by gas and dust.
04:07For example, when we look at dense clusters like the Messier 13, the stars are so close together that they
04:14look just like a white spot.
04:17Most of our telescopes can't separate them from each other.
04:19The satellite galaxy M32, our neighbor near the Andromeda galaxy, has about 84 stars per light year.
04:28It's so dense that stars can't be resolved even by the Hubble Space Telescope.
04:33To get the idea, our solar system is two light years long.
04:38We'd see about 168 stars outside our window if we were there.
04:44Our closest star is Alpha Centauri.
04:47It's about four light years away from the Sun.
04:49If it was just a couple of light days away, it would shine much brighter than the full moon.
04:55So if we somehow managed to survive in crazily dense star regions, the sky would be white all day long.
05:03But it's unlikely that we'd make it.
05:05As we get closer to the center of the Milky Way, the chances of finding life get super slim.
05:10The gravity of stars is going wild with chaotic movements, so there are barely any planets around.
05:17On those miracle planets, the radiation from cosmic rays is skyrocketing.
05:23Supernova blasts and star collisions nearby become an everyday occasion, and all the gas around makes it basically impossible to
05:31breathe or even see properly.
05:33At the same time, as we move further away, there are fewer stars around.
05:39Elements that are super useful for life like carbon, oxygen, and iron are produced by stars, so they also drop.
05:47Too much radiation is awful, but too low radiation means that there's not enough energy to support chemical reactions, like
05:54photosynthesis.
05:55Which is why, if there is extraterrestrial life, it would most likely be somewhere in the middle of different galaxies.
06:03But some galaxies get their brightness from a so-called active galactic nucleus.
06:09These are extremely energetic regions at the center of some galaxies.
06:14They shine much brighter than any stars imaginable, although it mostly shines only in certain parts of the electromagnetic spectrum.
06:21The brightness comes not from the stars, but from the accretion disk around their supermassive black holes.
06:29As the material slowly falls into a black hole, it gathers around it and creates this flat, spinning disk of
06:37gas, dust, and other stuff.
06:39Since the gravity and friction there are insane, this disk heats up and starts emitting enormous amounts of energy.
06:47Also, this disk spins incredibly fast, almost at the speed of light.
06:52Because of that, collisions there happen all the time, and they're unimaginably powerful.
06:58They release even bigger amounts of energy.
07:01Most galaxies don't have an AGN.
07:04Those that do, like the galaxy M87 in the Virgo constellation, are called active galaxies.
07:13There are also different types of AGNs.
07:16The Seifert galaxies, radio galaxies, and finally, the winners of our space brightness competition, quasars.
07:24Imagine things so bright that they can outshine the entire galaxy they belong to.
07:29Quasars are a specific type of active galactic nucleus, the most extreme and luminous form.
07:35They belong to the supermassive black holes, the biggest ones in our universe.
07:41Quasars are like a combination of several things.
07:44First, they're the brightest accretion disks in our world, because of their behemoth black holes eating everything around.
07:51But they have some cool features.
07:53For example, they have powerful jets of particles that shoot out from the poles of the black hole at nearly
07:59the speed of light.
08:00These jets add up to the brightness of the quasar, although they can only be seen in radio wavelengths.
08:08The energy they emit is so intense that they can be seen billions of light-years away.
08:13However, the nearest quasar to us is 600 million light-years away, so we can't see them with backyard telescopes.
08:21So, when we look at a galaxy through a telescope, we usually see only the brighter core, not the outer
08:27parts.
08:28Unfortunately, our eyes just aren't made to see things like the active galactic nucleus.
08:34So, these stars are the brightest things we can see.
08:37But what a beautiful sight it is.
08:40Does the universe ring like a crystal glass?
08:43Maybe.
08:44But it doesn't mean that it literally rings and we just don't hear it.
08:48It just vibrates.
08:51Many of you know that the universe started with the Big Bang around 13.8 billion years ago.
08:57I wasn't around then, but we can assume.
09:00The whole enchilada was born from a super-concentrated, hot, and dense, tiny dot that contained everything.
09:07When it couldn't bear its pressure anymore, it made a huge blast and spewed around all the time, space, matter,
09:14and antimatter like a pokeball.
09:16After being born, the universe moved at a breakneck speed.
09:21Imagine standing in the middle of nowhere, you blink, and suddenly you're surrounded by the universe.
09:26That's what it would feel like.
09:28It started growing and growing, and eventually, its speed got slowed down a bit by gravity.
09:33Gravity started pulling all the matter together, slowly helping new things like stars and galaxies to form.
09:41Okay, makes sense so far.
09:43The Big Bang gave the universe a big push accelerating it.
09:47Logically, everything should eventually slow down and start moving at a constant speed, or even stop, right?
09:53Well, nope.
09:54In the late 90s, astronomers discovered something weird.
09:58They looked at some supernova around us.
10:00And for some reason, these supernovas were super far away, much farther than they were supposed to be.
10:06In other words, the expansion of the universe is not only continuing after all these years, but it's even accelerating.
10:14After years of study, they discovered the concept of dark energy, a mysterious force that makes up about 68%
10:21of the universe's total energy.
10:23This energy pushes it to expand even faster over time.
10:27And now, scientists have proposed a new discovery.
10:31Perhaps the universe's movements are a bit, well, wobbly.
10:38It seems like the universe's expansion hasn't been smooth and stable over the years.
10:43Instead, it has undergone periods of speeding up and slowing down multiple times.
10:49Astronomers counted about seven cycles of this acceleration and deceleration over the history of our universe.
10:55This can be compared to the oscillation of a crystal glass.
10:59When you strike a crystal glass, it vibrates, oscillating at its natural frequency.
11:04It goes through fluctuations in which the frequency rises and falls.
11:08Over time, it calms down and fades away.
11:12Well, something like this is happening to our universe.
11:15You can imagine its speed also fluctuating like that, rising and falling, first super rapidly and then more calmly.
11:23As if it's not just different waves traveling through it, but our entire world is like one huge, ringing wave.
11:32The discovery was actually made by accident.
11:35Astronomers were working on dark matter modeling.
11:38They plotted a new graph called the Hubble diagram, which shows how big the universe got over the years, measured
11:44in supernovas.
11:46Supernovas are like some lighthouses of our world, helping us mark things on a map.
11:50That's when they found these oscillations.
11:53But we still need to check all the data to make sure that this discovery is indeed true.
11:59Dark energy and dark matter play this weird game with the universe,
12:03where one is constantly trying to pull everything together, while the other one wants everything to expand.
12:08So far, dark energy vastly outweighs dark matter, whose weight makes up only 27% of the universe.
12:16Now, both of them are invisible to us.
12:18And not just invisible to our eyes, like infrared.
12:22It's that we literally can't detect them in any way.
12:25We can only assume that they exist based on how they influence gravity,
12:29changing entire galaxies and all the large-scale structures of the universe.
12:33We basically made them up, because it was the only way to explain how our world works.
12:39Dark energy is uniformly distributed across space and time.
12:42And we're still not sure what exactly it is.
12:46Some theories say that it could be a property of space itself,
12:49quantum fluctuations, or even a new type of field or particle.
12:54But all we have for now is an invisible energy that pushes the universe to move very fast.
13:00If one day we learn more about it, this will help us predict the entire fate of our world.
13:05Depending on how exactly dark energy works,
13:08the universe may continue expanding and growing indefinitely.
13:12Or maybe one day, it will experience the big rip,
13:16where all matter will be completely torn apart.
13:19Okay, here's to hoping we're not all around for that.
13:22Meanwhile, dark matter, also invisible and yet to be proved, works the opposite way.
13:28It's not energy that accelerates things.
13:30Instead, it's more like a glue that tries to hold everything together.
13:34It's a type of matter we can't detect, because it doesn't emit, absorb, or reflect light.
13:40We don't even know what particles make up this thing.
13:43We still can't catch them.
13:44At first, we thought it might be made up of regular heavy particles,
13:48like the one that makes up our world.
13:50But after years of research, they haven't found even a single one.
13:54So now they think, maybe it's actually made up of ultralight particles,
13:59millions of times lighter than anything we know.
14:02And because of that, we can't even notice them properly.
14:05So now, astronomers try to detect not the particles themselves,
14:09but waves that they could leave as they move through space.
14:12But we believe that it exists,
14:15because if it didn't, our galaxies wouldn't hold together.
14:18Dark matter helps them form, grow, and rotate.
14:22So, about 85% of our world is made of something unknown.
14:27All of this is incredibly mysterious and needs a lot of research.
14:32But that's what we know now.
14:34Maybe in the future, we'll discover something
14:36that will completely change our perception of the universe.
14:39That's what happened to Albert Einstein.
14:41In the early 20th century, most scientists, including Einstein,
14:46believed that the universe doesn't actually move.
14:48They thought it was static, neither expanding nor contracting.
14:52That's because, to us, it feels like it doesn't really move.
14:55Back then, scientists didn't have powerful computers or telescopes
14:59that could detect all the little changes in the positions of stars and supernovas.
15:04When Einstein developed his famous general theory of relativity in 1915,
15:09his equations actually suggested that the universe
15:13should either be expanding or contracting.
15:15This didn't really make sense to him.
15:18To fix this calculation flaw, he decided to introduce a new term,
15:22the cosmological constant.
15:24It was like a repulsive force that counteracted the attractive force of gravity.
15:29Essentially, it meant that while gravity tries to push everything together,
15:33some force or energy helps to balance this out by pushing everything apart.
15:38Sounds familiar?
15:39Then, in the 1920s, astronomers Edwin Hubble and Georges Lemaître
15:44found out that the universe isn't static.
15:47It actually expands.
15:49They noticed a slight reddish tint from the distant galaxies.
15:52And this tiny hint meant that other galaxies were moving away from us.
15:57After that, Einstein scratched out the cosmological constant.
16:01Interesting how he was later ashamed of this assumption,
16:04calling it his greatest blunder.
16:06He didn't even know that he was a hundred years ahead of his time,
16:10accidentally discovering dark energy.
16:12Now the cosmological constant is back again, just in a new form.
16:17Something similar happened with dark matter.
16:20Scientists have already started noticing that something doesn't add up
16:24back in the early 20th century.
16:27They saw that galaxy clusters didn't have enough visible mass to hold them together,
16:31which means there must be some unseen mass that helps to make up for it.
16:36And that's when it got its name, the dark matter.
16:40This stayed unresolved and unproven for many years.
16:43And then it was finally discovered by Vera Rubin when she was observing galaxies and their movement.
16:49She realized that outward parts of galaxies move almost as fast as their central parts.
16:55This doesn't really make sense.
16:57The outer part should be a bit slower.
16:58This became the first official proof of dark matter which boosted its research.
17:04There are still many things left to be discovered.
17:07But maybe one day, we'll understand what is this invisible part of our universe that makes it ring.
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