The Universe: Countless Wonders of the Milky Way (S2, E4) | Full Episode | History

in the beginning there was darkness and then bang giving birth to an endless expanding existence of time space and matter now see further than we've ever imagined beyond the limits of our existence in a place we call the universe it's a crucible of creation and destruction the name milky way sounds like something kind of comforting sweet but the milky way galaxy is a monster it's just one galaxy among billions and we're living on the edge just recently we've discovered that there are two small galaxies colliding with the milky way right now it's a tapestry of

brilliant suns and blinding dust it's surprising how little of the light from our rather luminous milky way galaxy reaches us it's a place of extremes where stars can drift lazily or be flung out at more than a million miles per hour now scientists have pierced the galaxy's heart of darkness to find our way through the milky way it's a hundred thousand light years in diameter has a trillion times more mass than our sun it began about 13 billion years ago and is still under construction it's our galaxy the milky way the milky way galaxy is

an extremely active place it's like a construction project there's things going on all the time and you have old stars die and torn down and then that material it's used to build brand new stars in the midst of this work zone lies our little solar system and a whole lot more i suppose the best way to think of the milky way galaxy is our family of stars these are the stars that we travel through the universe with in a clump all orbiting at common center [Music] within its far-reaching spiral arms lie clues to where we

started and how it will all end on a clear summer night the stars of the milky way unfurl like a shimmering banner across the sky ancient egyptians saw this river of stars as a pathway to the afterlife but the greeks were the first to name it the milky way comes from the word galacos which is greek for milk and though we once believed we lived at the center of the universe we now know that we don't even live in the center of our own galaxy when we look up into the night sky and we see

this milky swath of stars that we call the milky way what we're actually seeing is a spiral arm of the galaxy that's closer to the center of the galaxy than we are we can't really see the center of the galaxy from here but what we can see is one of the spiral arms that's a few thousand light years closer to the center than we are as we gaze at the milky way from our earthbound position it's like looking at the edge of a coin we get no sense of the galaxy's real shape if however you

look at a galaxy from the top down it's a disk remember and it looks it's like looking at a frisbee from the top down you can see its full glory even though it's thin you don't see how thin it is but you see its full structure [Music] you can make the analogy of the milky way as being very much like a city there's a central region there's big buildings there's a lot of action in the middle and that's certainly true of our galaxy then you move out to the suburbs where life is a little bit

more comfortable a little more relaxing it's a better place to raise a family this is where we reside our solar system is among the milky way's spiral arms 26 000 light years from the bustling center our galaxy is so large that it takes earth more than 200 million years to make one lap the sun is located in what would be just an average neighborhood around the city center but again if you're standing in the middle of this neighborhood you don't really know what the neighborhood on the opposite side of the city looks like because you

can't see it directly as we move outward beyond the suburbs the population becomes more sparse and yeah you've even got sort of the boondocks in our galaxy you've got the halo where you have very old stars in sort of wide orbits around the galaxy the galactic sprawl doesn't stop at the milky way's loose and undefined halo it reaches far beyond our neighborhood and out to a group of galaxies called the local group if you think of the milky way galaxy as a city like los angeles then you can think of these as counties all within

the state of california and together this local group makes up the entire state besides our huge milky way and the even larger andromeda galaxy the local group consists of close to 50 smaller galaxies the closest of which are roughly 40 000 light years away there are two relatively nearby dwarf galaxies the large and small clouds of magellan that orbit our milky way galaxy and are easily seen in the southern hemisphere they're small little galaxies but our local group has several dozen such galaxies sort of wandering around inside it the big galaxies are the minority one

advantage of actually being in the outer edges of our galaxy we have a clear view of outside of our milky way we're able to see the rest of the universe our neighboring galaxies and galaxy clusters beyond our own local group of galaxies inside the milky way's halo lie massive globular clusters globular clusters are densely packed regions of stars that are all of similar composition these are like the ethnic neighborhoods of the milky way galaxy indeed these globular clusters formed when the galaxy was very young they are among the first stars to have formed some globular

clusters are 12 or 13 billion years old they contain a hundred thousand or even a million stars globular clusters almost as old as the universe itself gave us the first clue to our place in the galaxy we saw these globular clusters in the sky but their center was somewhere far away from us and that was one of our first measurements of where the middle of the galaxy should be it weren't orbiting around us but around an area somewhere about twenty seven thousand light years away we can never get far enough away from our own galaxy

to actually see it but by looking at other galaxies and comparing what we know about our own galaxy we've got a pretty good picture of the milky way the very first time we saw galaxies through telescopes we didn't even know they were galaxies i thought they were just nebulae in our own galaxy and we were just amazed by the beautiful spiral shape so it was sort of natural for astronomers to classify galaxies according to their shape what we see astronomers recognize four basic galactic shapes elliptical built of old stars and which doesn't spin lenticular consisting

of a bulge and a disc and little or no new star formation irregular which has no real shape at all like the magellanic clouds in our own local group and spiral which includes our milky way it's a pinwheel of young and old stars spinning gracefully through space a long time ago people thought that maybe an elliptical galaxy eventually collapses down into a spiral or maybe eventually spirals all come together and form an elliptical and it was sort of hard to figure out exactly what the sequence is one thing we know is that elliptical galaxies tend

to be very large [Music] centaurus a a misshapen elliptical galaxy about 13 million light years away suggests why elliptical galaxies get so big there's a lot of evidence that there's a spiral galaxy in there somewhere that got absorbed by a larger galaxy so right now it's possible that these really big elliptical galaxies we see may be the mergers of several spirals and other types of galaxies our milky way isn't in danger of being absorbed anytime soon but the heart of our spiral galaxy has revealed a secret of its own only recently we discovered that the

milky way is not a classic spiral but a barred spiral there's a bar of stars going through the center and the spiral arms sort of attach off from that bar spanning 27 000 light years it's the most popular bar in the galaxy 30 million stars gravitate to it the bar of our galaxy is natural result of gravity the mutual gravitational interactions of the individual stars that form the disc of our galaxy and the bulge of our galaxy causes sometimes the stars to sort of bunch up into this bar configuration surrounding the middle of the milky

way is a huge central bulge it's mostly composed of stars between 10 and 11 billion years old the size of the bulge is linked to the milky way's most gripping feature of all a super massive black hole though it would easily fit in the space between the earth and our sun it's four million times more massive than our sun now that sounds like a lot but other galaxies have central black holes which extend up to a billion times the mass of our sun so whereas it's a we call our black hole at the center of

our milky way a supermassive black hole among supermassive black holes it's kind of a runt black holes can't be seen directly because light can't escape them astronomers have located galactic ground zero through a radio source in the constellation sagittarius known as sagittarius a star it's creating quite a stir the black hole in the middle of our galaxy is spinning and it appears to be spinning at a rate of about one spin per 11 minutes as it spins central region stars caught in its gravity gets swept along for the ride orbiting it at about 3 million

miles per hour the black hole affects the central region the most but we can't feel its tug on earth since we orbit the galaxy far away from the center the colossal forces at the galaxy's heart are negated by the milky way's unimaginable size to me the name milky way sounds like something kind of comforting sweet you know a candy bar that sort of thing but the milky way galaxy is a monster it is incredibly huge so when you think about how vast our solar system is the fact that it takes years for the fastest spacecraft

to get out to saturn or jupiter if the entire solar system were the size of a cd the earth would be comparable to the milky way that's huge that's absolutely mind-blowing and it never ceases to amaze me and the amazement goes on and on the galaxy's bustle and commotion may be concentrated in the center but the spectacular spiral arms have action of their own it's here that stellar neighborhoods are being built and stars are being born this is our galaxy it's a lot to take in and we're just beginning to probe its depths our suburban

location makes it difficult to get the big picture and the hazy clouds of cosmic dust only block our view even the most powerful optical telescope can't pierce the darkness so if we want to learn more about the milky way we need to look beyond what our eyes can see for all its vastness and empty space the milky way is tremendously active and populated with some astonishing phenomena star clusters nebulas blazing invaders from other galaxies technology is making us rethink old beliefs and is showing us things we've never even considered before plus 15 seconds sending the

new horizon spacecraft on its way to the very edge of our solar system we live on a dusty planet in a dusty galaxy in a dusty universe empty space isn't so empty optical telescopes can see only as far as the nearest dust cloud which isn't far at all most of our galaxy is invisible to us however and that's because the galaxy is full of dust dust clouds if you will and these dust clouds block the light from most of the stars in our galaxy it's surprising how little of the light from our rather luminous milky

way galaxy reaches us the reason for that is simply because the dust blocks it but visible light is just a small sliver of the energy spectrum and radio waves rush in where visible light beams fear to tread on a foggy day you might not be able to see very far at visible wavelengths which your eye can see but you can still listen to your radio or watch your tv the ability of radio waves to penetrate space dust is crucial to the study of the stars but that use was discovered by accident in 1933 karl jansky

an engineer at bell labs in new jersey built an antenna to track down the source of static on transatlantic telephone lines he was surprised to discover the interference was raining down from the center of our galaxy the constellation sagittarius it took several decades for scientists to realize that jansky was onto something celestial bodies emit electromagnetic radiation and thus radio astronomy was born but radio waves were just the beginning because the human eye can't see all the light that's available we have to resort to technology and one of the best ways of seeing the universe in

a very different way is with an infrared camera an infrared camera sees only the wavelengths generated by heat then converts it to something the human eye can see there actually is no visible light at all that passes through this lens this lens only lets heat light through and then you can see what everything looks like in infrared light three two main engines start in 2003 the spitzer space telescope equipped with a battery of infrared cameras was launched into space its mission is to explore some of the youngest stars and farthest galaxies in the universe the

instruments that spitzer has on it are actually many times millions of times more sensitive than these cameras but they're basically the same thing this camera doesn't peer into the heavens but is used by firefighters to save lives right here on earth the camera can see through a smoke-filled room to read the body heat from an unconscious or immobilized victim the same technology has enabled astronomer susan stolovy to see 26 000 light years away visualizing the center of the galaxy as never before this high resolution mosaic was assembled from roughly 12 000 individual images taken from

the spitzer space telescope even though that sounds like a lot of data and it is it only took about 16 hours of telescope time this particular region of the galactic center spans an area of the sky that's equivalent to four full moons in one direction and three full wounds in the other that's the equivalent of 900 light years across by 700 light years high a small fraction of what's out there to see but a phenomenal achievement nonetheless just a few decades ago the galactic center was not a subject of study because you couldn't see it

visually nothing gets through only one light wave and a trillion can penetrate the dust but if you go into the infrared or use radio astronomy or x-ray astronomy you can see what's going on there different wavelengths of the electromagnetic spectrum can reveal different aspects of the galaxy because they penetrate celestial objects differently [Music] radio waves have the lowest energy or longest wavelength but most celestial objects emit them then comes infrared visible light ultraviolet high energy x-rays with wavelengths about the size of an atom are emitted by black holes and supernovas the highest energy gamma rays

come from the collision or decay of subatomic particles like when stars explode at billions of degrees together these waves give astronomers a more complete picture of the activity and shape of our galaxy many if not all of the wavelengths are needed to study the cosmos the various wavelengths of the electromagnetic spectrum are similar to the strings on a violin in music many wavelengths of sound are used to communicate a musical idea this piece has a very large range from a low note to a high note if we were to restrict ourselves to the visible light

spectrum it's almost as if we were only to hear two notes in the middle of that piece using alternate wavelengths the more we look the more we're discovering just recently we've discovered that there are two small galaxies colliding with the milky way right now and the only reason we didn't know they were there is because there was so much dust in the disk of our galaxy we couldn't see them we're living inside this cloud and it's something we're not aware of but with infrared light you can cut through that dust and the minute we turned

infrared telescopes to the sky we saw these little galaxies up there coming right at us [Music] from our cockeyed position in the milky way it's difficult to gauge what our galaxy really looks like radio and optical astronomy give us a glimpse of its features but to get the big picture we need to look outward so the way we gain some understanding of our own galaxy is first of all by looking at other galaxies and seeing what they look like and seeing things in other galaxies that correspond to things that we see in our own galaxy

like clouds of gas that are kind of lined up along what looks like a spiral arm you know we can see parts of spiral arms in our own galaxy and we figure that they're all connected kind of like the spiral arms of other galaxies that we can see from the outside we know that the milky way's four main spiral arms swing out from the downtown center like wide streets from the inside out they're named norma scudum crux sagittarius and perseus if the arms are the galaxy's suburbs then our solar system lives on a quiet dead-end

street between sagittarius and perseus on what's called the orion spur all the stars in the milky way add up to a community of about 200 to 400 billion and they're on the move we are orbiting around the galaxy we change our position so far we think the sun has always been about the same distance away from the center but we've been in and out of pretty much every spiral arm that there is the spirals are called density waves areas where the stars and gas get pushed together as the density waves spiral around the billions of

stars ride over and through them when you think about watching the tour de france and you see all of these bicycles they're all moving forward sometimes they kind of clump up around one bicyclist and sometimes they're stretched out that's sort of what the spiral arms are like that the stars are going around like the bicyclist sometimes in clumpy areas and sometimes in more spread out areas but they keep going around the center stars don't usually travel alone while giant globular clusters populate the galaxy's halo the galactic disk has open or galactic clusters these bundles of

young stars are barely held together by their mutual gravity now open cluster implies that the stars are actually free to go it is open so this is a cluster usually of many stars that have formed together all from one of these giant clouds of dust and gas over time they're going to move away from each other distribute themselves around the galaxy astronomers have counted about 20 000 open clusters in the galaxy the pleiades is the one found nearest to the earth it formed a hundred million years ago and will be around at least twice that

long before the galaxy's spiral arms tear it apart closer to home our own sun orbiting in solitude may have once been part of an open cluster star that struck out on its own the sun the star clusters our own planet in fact the entire galaxy and the universe beyond are built of dust and gases these particles that now block our view are what got us here in the first place and the star-making machinery is still cranking nothing beats the spectacle of a glorious sunset but we owe it all to dust and gas the setting sun

appears yellow orange or even red for two reasons first of all the molecules of air in the atmosphere are scattering the violet blue and green light out of our line of sight leaving the yellows oranges and reds to reach our eyes and second of all particles like dust or smoke or smog in the atmosphere absorb blue light more than they do red light even the grandeur of a blue sky is really an optical illusion why is the sky blue there's nothing blue about the gases of our atmosphere but as sunlight comes through our atmosphere the

shorter wavelengths the blue light gets scattered more than the longer wavelengths do so if you look at any particular part of the sky you're more likely to see blue light being scattered towards your eye space is dark because there aren't enough gas or dust particles to reflect the light of a billion stars and though space may be a vacuum it's not perfect the galactic disk the largest portion of the milky way owes about 15 of its mass to dust and gas gas clouds can span hundreds or even thousands of light years providing the raw material

that fires the galaxy these regions of cosmic dust and gas are called nebulae and they produce effects rivaling anything seen on earth a good example is the orion nebula in the constellation orion this region is active with stellar formation which makes the gas around the stars glow it's literally fluorescing in response to the light coming out of the massive stars that are near the nebula and this nebula literally glows and can be seen you can see it with your naked eye when you see the orion nebula in a real way those are baby pictures for

us five billion years ago we were in a glowing hot nebula and the sun and the planets were forming together under the influence of gravity orion which contains hot stars ionizing its gases with ultraviolet light is called a diffuse or emission nebula astronomers classify two other categories of nebulae some nebulae are what are called reflection nebulae they're simply the dust in these nebulas simply reflecting the starlight from the bright star nearby the witch head nebula is an example of a reflection nebula borrowing light from the star rigel reflection nebulae appear blue for the same reason

our sky does blue light is more easily reflected than red and last there are dark nebulae like the horse head when low-mass stars like our sun die they form another kind of nebula called a planetary nebula these dim short-lived nebulae like the cat's eye nebula spew elements back into the galaxy these may become raw materials for new suns and new planets just as dying stars spew out clouds of dust and gas dust and gas can come together to form stars at a construction site you have old buildings being torn down and new buildings going up

and it's very much the same in the milky way galaxy you have old stars explode and they cast out new material raw material gas and dust that can be used to form new stars [Music] nebulae are the galaxy's recycling centers where old becomes new again recycling is not just a good idea here on earth it's a natural cosmic law in fact our own bodies are made out of recycled material from earlier generations of stars that had dispersed material into the interstellar medium before our own solar system formed each generation of stars creates heavier elements which

become the ingredients for everything in the universe most of the galaxy's hot young stars get built in the milky way's spiral arms as gas clouds orbit the center of the galaxy like the stars do they get squeezed as they go through a spiral arm remember a spiral arm is simply a wave in the pattern of stars and because stars are denser there the gas clouds that orbit through it tend to get compressed that compression allows gravity to get a hold of that gas and cause it to collapse to form stars more readily there than anywhere

else stars often die in the spiral arms because they are formed here more frequently victims of their own enormous mass the more massive stars are extremely powerful extremely luminous and to be that luminous they have to use up their their energy source very quickly so massive stars live only short lives and they are thus found in or near their birthplaces the spiral arms because they simply don't have enough time to wander away from the places where they were born although we can anticipate the future of some stars it's often difficult to learn their history but

new techniques are revealing new secrets about a well-studied star in the milky way called myra a myra has actually been a favorite star of astronomers for 400 years it's a very easily visible star in the night sky recently the galax spacecraft the galaxy evolution explorer photographed myra in invisible ultraviolet light and revealed that it's leaving a trail 13 light years long behind it we think that's actually caused by the fact that as the star plows through the gas the gas heats up in a bow shot very much like waves breaking up against a boat and

then that streams out into a wake of hot material you're actually looking at myra acting very much like a boat plowing through the water when you look at how fast myra is going right now about 291 000 miles an hour and you do the calculations that long tail is its path the last 30 000 years we can't predict exactly where the sun will go in its orbit around the milky way there's all kinds of things that could interact with but here we have the history of one star we know this is the path it took

and that'll help us model how the galaxy works and how all the stars move around the middle of the galaxy within the milky way's suburban spiral arms young stars enjoy plenty of space to move around as we move into the galactic bulge conditions get much more crowded and urban closest star to the sun is a little more than four light years away and when we look up into the night sky even on a perfectly clear night with no lights around you can't see more than about two or three thousand stars but if our planet was

down in the middle of the galaxy there would be a million stars in the night sky as bright as the brightest star that we've ever seen in our sky and it would be so bright that in fact it wouldn't be nighttime it would be daytime all the time life as we know it would be completely different so what do we owe our position to scientists believe that gravity has a lot to do with it gravity is the power that drives the galaxy and at the galaxy's center churns the engine it feeds galaxies are like a

city in that they are ever changing and you're constantly being rebuilt and reinvigorated there's no question that the milky way a few billion years ago looked a lot different than it does today it probably was smaller it probably didn't have the beautiful spiral shape that we see today as things collapse under gravity you tend to naturally form a disc you'll notice there are discs everywhere our solar system is a disc our galaxy is a disc so the stars all start rotating in the same direction just as in a city not all the stars in the

galaxy are natives some stars born beyond the milky way settle here and begin to make their mark but then if another galaxy comes by the gravity affects the way the stars move and this may initiate the spiral arms so in fact our spiral shape may be some evidence that the milky way is composed of more than one small galaxies that came together a long time ago historically the center of the galaxy has been an impenetrable mystery until we developed x-ray vision one of the first ways we really identified where the exact center of the galaxy

was was with an x-ray telescope well the x-rays were able to pass through all of the dust and gas in the disk of our galaxy and so even though we can't really see this bright center to the galaxy in x-rays there's this giant glowing hot source right in the middle the x-ray emitter sagittarius a star is associated with the super massive black hole in the milky way's center by definition a black hole doesn't allow light or even x-rays to escape the radiation comes from gas caught in its gravity spun and heated to millions of degrees

they're moving at extremely high velocities for example the more extreme cases that we've been able to observe the stars are moving as they pass by the black hole at a speed of 10 000 kilometers per second that's like going around the world in four seconds and we're talking about a whole star moving at that speed when we watch stars orbiting the very center of our galaxy it's obvious that there's some sort of invisible monster there they're orbiting around a giant mass and the orbits of the stars imply that there's about three to four million times

the mass of the sun in the very center of our galaxy we're not sure which came first the galaxy or the black hole but we know that it's there and it's tremendous for all its power and weirdness the supermassive black hole is pretty typical for a galaxy the size of the milky way other spiral galaxies and big elliptical galaxies also seem to have supermassive black holes in their middle ranging from a million times the mass of our sun up to several billion times the mass of our sun the stars surrounding the black hole are ancient

many are red giants hundreds of times bigger than our sun the galactic center is crowded with them like an urban downtown crowded with people and stars like people can be pushy most stars in the gladiator center simply just keep orbiting the central black hole but in the galactic center there's so many stars packed so close together that stars are constantly nudging each other a little bit gravitationally and their orbits are being perturbed changed a little bit a bump star can get stripped of its atmosphere leaving just its orbiting core or rarely it can tumble into

the black hole and vanish but something else is happening around the black hole this turbulent dangerous neighborhood is also a stellar nursery the stars that we're observing moving fastest around the black hole are the young stars that uh have very recently formed and it's something we call the paradox of youth because it's it's hard to imagine how to form these massive young stars in the presence of a black hole and yet there they are recently astronomers discovered that not all stars caught in the black hole's grip are doomed to stay there a few managed to

break away and see the universe barreling through the universe at one and a half million miles per hour hyper velocity stars are the escapees of the galaxy and what's interesting about high velocity stars is the only way to explain their extreme velocities is that they're rejected by a supermassive black hole for a star to go ballistic takes a very specific set of circumstances and in fact it requires two stars most of the stars you see in the sky are not single stars but pairs or binary stars they orbit around each other linked by gravity's embrace

but a star pair in the galactic center might get jostled by surrounding stars and stray too close to the black hole when that happens the moment that the gravitational pull of the black hole exceeds the gravity that's binding the two stars together the pair of stars is broken apart one of the stars will be captured by the black hole usually into a very tight orbit around the black hole and the other star will then gain all the energy of that system and be ejected with this incredible velocity if the galaxy were a city where most

of the stars would be cars or pedestrians a high velocity star would be more like an airplane or a high-speed train rushing out of the country if you're on high flossie star the ride would be quite amazing the sky would be covered with stars as bright as the full moon in every direction but that view would quickly change because the hypoplasty star moved so quickly out of the galaxy the stars appear fewer and fewer in the night sky the galaxy is constantly in motion like a giant wheel or a sprawling metropolis in the heart of

town the supermassive black hole's gravity whips stars around in an orbit of around 11 minutes where the earth sits two-thirds of the way out on a spiral arm we traverse the milky way once every 250 million years our solar system has been around the block only 18 times since it formed the milky way's incomprehensible size makes it easy to forget it's just one small part of an expanding universe when people hear about the expanding universe a common misconception is that everything is expanding and in fact i'm not expanding right now my atoms are the same

size my cells are the same size the earth is not getting farther away from the sun the expansion of the universe only applies to celestial objects that aren't bound together by gravity since the planets within the milky way have stronger gravitational pulls than the expanding forces outside our galaxy the expansion of the universe doesn't affect our solar system our own milky way a spiral galaxy is on a collision course with another spiral galaxy the largest spiral near us and that is the andromeda galaxy we think that in maybe three or four billion years our two

galaxies may merge together it'll be very interesting to see what happens what probably won't happen is a collision of stars even though both galaxies contain billions of stars the space between them is enormous they will gravitationally interact changing their direction and motion eventually the merged spirals will settle down to become an elliptical galaxy essentially all of the several dozen galaxies in our local group will be part of one super galaxy and then gradually that super galaxy will start losing stars because of gravitational interactions among the stars within that galaxy some will get flung away into

intergalactic space when it first formed the milky way built stars at a rapid pace using raw materials that were ejected in space from the big bang as the galaxy aged the star production slowed down from a few hundred a year to about four to six new stars each year today over time the milky way galaxy has changed dramatically and we don't know exactly what it looked like long ago but probably early on there was a lot more gas and dust and probably fewer stars and you had a lot of very large very massive stars that

would have formed early on and then these early stars exploded fantastically and spat out new material heavier metals that could be used to form smaller second generation and then third generation stars [Music] some younger galaxies are still enjoying that kind of building boom we can see some galaxies where the rate of star formation is very high compared to our galaxy those are called starburst galaxies the rate of star formation there can be anywhere from 10 to 100 times what it is now in our galaxy with every generation star production slows down and the milky way

has been in business for 13 billion years one of the reasons that the rate of star formation in our galaxy has changed over time going from a very high rate to the current modest rate of star formation is because the gas is being used up gas is used up to form stars and we're running out of gas literally eventually over trillions of years star formation will stop completely the great galactic construction project will shut down and one by one the twinkling stars will fade away you