Sagittarius A*: The Milky Way's Supermassive Black Hole

this video is brought to you by surf shark  safety and security online are critically   important and you can protect  yourself online with sur shark   get 83 off and three months for free  through the link in the description below far away from earth in the constellation  of sagittarius so far it takes like 27   000 years to reach it lurk's a star devouring  monster located at the very heart of the milky way   this monster measures some 44 million kilometers  in diameter with a mass equivalent to over 4.3   million suns it accounts for 99.9 percent of all  mass found at the center of our galaxy yet this   creature isn't some fictional lovecraftian elder  god slumbering on the edge of space no it's deadly   real the product of physics even if the laws  of physics themselves break down at its center   known as sagittarius a star it's our local  supermassive black hole for most of human   history the existence of this galactic scale of  earth and was a mystery as alien to our ancestors   as gravitational waves or the higgs boson it  was only in the 1930s when we began detecting   strange radio signals from the heart of our  galaxy though we realized something utterly   fascinating was lurking out there something we're  still battling to understand to this very day it was at the height of summer 1931 when karl g  yansky made his eerie discovery a radio engineer   of czech french descent yansky had been hired  by bell telephone laboratories in new jersey   to locate sources of static that might mess up  their communication systems to do this he'd built   what is considered to be the world's first radio  telescope a strange looking array of antennae   and wheels that must have seemed like science  fiction to his contemporaries but when yansky   began using it to hunt for sources of static he  stumbled upon something truly remarkable way up   in the sky a strong radio signal was emanating  from the heart of the milky way specifically from   the constellation of sagittarius yansky had no way  of knowing it but he'd just become the first human   being in history to detect a signal related to  our galaxy's supermassive black hole these days   of course we have a much greater understanding  of sagittarius a star we know for example how   heavy it is with a mass equivalent to 4.3 million  suns we know too how large an area it covers with   a radius of 22 million kilometers you could swap  our sun for sagittarius a star and its outer edge   would almost reach mercury yet for all we think  we understand this behemoth there's still a lot   about it that boggles the mind for instance we've  known for years that our supermassive black hole   flashes irregularly sending out seemingly random  bursts of bright radiation the only known black   hole to behave this way weirder still we know  also that it's leaking at the beginning of 2022   nasa announced that sagittarius a star had been  discovered to be emitting superheated material   for thousands of years likely the after product of  a star or gas cloud devoured long ago yet despite   all of this seemingly intense activity sagittarius  a star is also notable for something else and   that's how unusually quiet it is although it might  be a colossal radiation emitting titan from our   perspective compared to other supermassive black  holes it is more like a fat contented cat napping   peacefully in a sunbeam according to scientific  american this is because sagittarius a star   is in a dormant phase like a post lasagna garfield  wear it in the active quick eat everything before   john gets home phase the radio signal yansky  detected back in 1931 could have been up to   a billion times more powerful yet this doesn't  mean our local supermassive black hole is always   slumbering in the not so distant past it may have  been terrifyingly active one of the slightly gross   things about supermassive black holes is they like  barney gumbel after too much duff often burp but   while barney belching is only gross if you spend  too much time in moe's tavern the supermassive   black hole equivalent is utterly cataclysmic as  more and more material falls into the monsters   more the magnetic and gravitational forces  superheat the surrounding gases to millions of   degrees things eventually get so intense that some  of the gas gets ejected out as an enormous jet of   high-energy particles blasting tens of thousands  of light years into space loaded with x-ray and   ultraviolet radiation these burps can devastate  anything in their path one recent study has shown   that were sagittarius a star to burp on earth it  would strip our atmosphere away fortunately we're   too far away for that to happen our planet would  have to be ten times closer to be at risk of these   killer belches but we can still see traces of past  events expanding out of the top and bottom of our   galactic disk are two enormous blobs of hot gas  each one weighing millions of times more than our   sun known as fermi bubbles the largest one extends  23 000 light years upwards into space estimated to   be 6 million years old they're evidence of  a recent ish time when sagittarius a gorged   itself like crazy yet while this particular  feast happened millions of years ago there's   evidence that most supermassive black holes have  far shorter cycles perhaps leaving as little as a   hundred thousand years between feeding frenzies if  this seems wild though you should probably prepare   yourself to understand the story of sagittarius a  star we first need to try and wrap our head around   what supermassive black holes really are and  believe me things are gonna get pretty weird when confronted with the fact of a gigantic  black hole squatting at the heart of our galaxy   the logical question seems to be well how did  it get there what's so special about the milky   way that it gets its own monster my answer is  nothing there's nothing special about it at all   in fact it seems that almost every galaxy above a  certain size has its own massive black hole like   sagittarius a star these other giants sit at the  very center of their galaxies unlike sagittarius   a star though they can be seriously supermassive  as far as we can tell the size of a supermassive   black hole is inextricably linked with the size  of its host galaxy the more mass the galaxy has   the bigger the black hole now with such a clear  correlation it might be tempting to think that   these behemoths are somehow responsible for  galactic formation that without them the structure   of the universe would be completely different  except there's no hard evidence that this   is the case just as there's no hard evidence that  large galaxies inevitably create supermassive   black holes the snappily named a2261 bcg for  example is a galaxy of absolutely gargantuan   proportions 10 times larger than the milky way  yet it seems to be missing a central black hole   still the vast majority of large  galaxies do appear to have them and   many are far far more active than sagittarius a  quasars are ancient supermassive black holes that   are so active they've basically ignited the entire  core of their galaxy we've so far identified more   than a hundred thousand of them each powered by a  black hole beating frenzy that's beyond anything   our galaxy has ever seen and speaking of power if  there's one thing these monsters are capable of   it's energy production you've probably heard of  the concept of an event rise and the boundary   around a black hole from where the gravitational  pull gets so great that not even light can escape   but just before you cross that horizon things  get seriously energetic when a supermassive black   hole is spinning it can pull in material around it  into a superheated disc known as an accretion disk   it's from the incredible temperatures in this disc  that the insanely bright signals blasting out from   quasars come from lighting up the night sky more  ferociously than millions of stars and perhaps no   wonder black holes are thought to transform mass  into energy with a 40 percent efficiency which is   way beyond even what a nuclear reaction is capable  of as black hole researcher barter voluntary put   it to the bbc in 2021 black holes are the most  effective energy efficient engines in the universe   it's this massive energy conversion that allows  us to see an object that by definition doesn't   reflect any light remember that incredible photo  from 2019 showing the first ever image of a black   hole while that was only possible thanks to  the accretion disk swirling brightly around it   allowing the creature at the center of messier  84 to cast a visible shadow but taking that photo   was a time-consuming process involving the use  of a global network of radio telescopes when we   want to take a peek at a supermassive black hole  there are far easier ways one method is to forget   about the accretion disk and instead focus on the  stars closely orbiting it this is what we do when   we want to look at sagittarius a star using the  orbits of stars like s2 to calculate the forces   at work from there we can draw a pretty good idea  of what the black hole itself must be like another   way more sci-fi method is using gravitational  waves only detected for the first time in 2015   gravitational waves are ripples in the fabric of  space time flowing out at the speed of light from   mergers between incredibly dense objects although  we can't pretend to understand the theory here   actual expert professor paolo pani told the  eu horizon program in 2019 that they could   be used to view black holes as a report on his  interview summed it up by studying the features of   these waves it is possible to obtain information  about the mass rotation radius and speed of these   previously invisible objects again look  we're youtubers we're not cosmologists we   can't pretend to wrap our small brains around  this but we do know that it's great news the   more we learn about objects like sagittarius a  star the more we understand the universe itself   and that is no exaggeration because aside from  being weird as supermassive black holes represent   a tantalizing mystery we currently have no idea  how they got so massive in the first place now   just before we continue with the rest of today's  video let me tell you about today's wonderful   sponsor sir shark do you use the internet of  course you do you're on the internet right now   do you have personal information that you'd rather  remain personal of course you do who doesn't well   let me tell you something the internet is a weird  place there are people out there that want to ruin   your day or your week or even your months they  want to steal your details steal your identity   unfortunately that's a thing and it can be  a real pain in the ass well serve shark has   hack lock this searches databases for your  passwords which sounds bad but don't worry   if they find 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but it presents a  problem there's no way that a regular black hole   formed from a collapsing star could ever grow  as big as sagittarius a star that's not to say   they can't grow as they devour more matter they  absolutely do but the rate of growth is so slow   that even if you assume a really big star once  existed that collapsed into a black hole just   200 million years after the universe was born you  still wouldn't have enough time for it to grow to   the supermassive size that it has today and that's  when you've got 13.5 billion years to play with   but we already know the first supermassive black  holes appeared long before that those quasars we   mentioned well because they burn so bright many of  them are visible to us from the very edge of the   visible universe that means we're seeing them from  almost the dawn of time around 600 million years   after the big bang to use a slightly goofy analogy  finding black holes with masses millions of times   that of our sun so close to the dawn of time and  assuming they just grew from regular black holes   is like finding an elephant in a crash and just  assuming that it's a deformed child that had a   sudden growth spurt they're clearly different  beasts so where did sagittarius a star and all   of its overgrown brethren come from one popular  theory suggests they grew from seeds the idea   goes that maybe there existed a size class of  black hole that's way bigger than regular but way   smaller than these galactic monsters created from  collapsing dust clouds at the dawn of the universe   these welterweight black holes formed when the  universe was so cramped that they had endless   matter to gorge on and since they were already on  the big side to begin with it took them less time   to consume things and become supermassive this  is the most likely explanation but it's also   one that runs into problems one is that there's  no certainty early giant gas clouds would have   collapsed so spectacularly the other is that even  with this head start it's not certain the laws of   physics would allow the seed black holes to  grow so big so fast another possibility is   collision theory nearly all large galaxies with  their own sagittarius a star show evidence of   having collided with another galaxy at some point  this has previously happened to the milky way and   it's destined to happen again when our galaxy  goes leaping into andromeda's big manly arms   in about 4.5 billion years given these constant  collisions it's possible that today's supermassive   black holes are the result of billions of years  of black hole mergers again though this idea runs   into problems although most galaxies show signs of  having been in collisions not all of them do there   are a handful of galaxies out there that have  seemingly never crashed into a neighbor annoyingly   they also seem to have supermassive black holes at  their center effectively killing this theory that   leaves only options that take us way outside of  our comfort zones the first two involve something   that everyone has heard about but has never been  detected dark matter in a nutshell dark matter   is a theorized particle that is thought to make  up 27 of all mass in the universe it may also be   where supermassive black holes come from according  to one theory sagittarius a star and others may   have formed from dark matter itself according  to an even wilder theory sagittarius a star   may in fact be dark matter this one comes from  a study published in spring of 2021. in it the   researchers argue there's no black hole in our  galaxy center massive or otherwise instead there   are clumps of dark matter that are so vast they  mimic the effects of a black hole while being   just weak enough to allow clouds of gas to pass  by undisturbed something that has been documented   happening around sagittarius a star the final  far out theory involves primordial black holes   these are hypothetical black holes that were  created at the birth of the universe and they   could have been formed already at a gargantuan  size before the first stars ever appeared as with   dark matter though their purely theoretical  nature makes actually testing this theory   pretty much impossible putting it firmly into  the wild speculation zone all right so that's   what we sort of do and mostly don't know about  supermassive black holes and it naturally leads   to another fascinating question how did we  discover so much about them in the first place   it was just before christmas 1915 when albert  einstein received an unexpected gift about a   month earlier the great scientist had published  his paper the field equations of gravitation   laying out further the relationship between  matter and space-time as well as publishing   einstein had also sent a copy to his friend  the german physicist carl schwartz child who   was then fighting on the front lines of  world war one but rather than be all like   cool paper bro schwartz's child had taken time out  from the miserable grind of life in the trenches   to write back with a solution it was a solution  that suggested how a star could theoretically   exist of such high density that not even light  itself could escape its pull in other words   the first description of a black hole originally  called frozen stars they were for a long time only   a mathematical curiosity a weird anomaly that  couldn't possibly exist in real life indeed   einstein himself argued in 1939 that they  were impossible by then schwarz's child was   long dead having died from disease way back in  1916. yet it would be schwarzschild who history   eventually proved right the revelation that  black holes were terrifyingly real came in slowly   effectively in parallel with our discovery of  their supermassive cousins by the time einstein   was dismissing the idea in the late 30s karl  yansky had already detected the first signals   coming from sagittarius a star not that anyone was  desperate to find out what it was since yansky's   discovery had no connection to communications his  employers refused to fund his study further and so   investigation into what yansky called star noise  would be put on hold for decades critically though   humanity would return to it at around the  same time that we finally began to discover   the first regular black holes the 1960s were  an exciting time for astrophysicists in 1964   a bright source of x-rays known as cygx1 was  found in the night sky eventually found to be   the first known black hole around the same time  scientists were making massive strides towards   uncovering their supermassive counterparts the  early 1960s saw the discovery of quasars what we   now know to be extremely ancient extremely large  black holes igniting the cause of far distant   galaxies likewise interest was growing in what  had come to be known as radio galaxies galaxies   emitting strong radio sources they had long  puzzled scientists especially because the signals   seemed not to be coming from the galaxies  themselves but from giant lobes projecting above   and below the galactic disk today we know this is  the result of a supermassive black hole belching   out of two ends at once like that gross kid in  elementary school who's mastered simultaneous   burping and flatulence back then though these  radiolobes were a mystery until scientists in the   1960s discovered the thin jets leading from these  bubbles back to the galactic center as they looked   into it more and more they started to realize that  the source of these jets must be tiny smaller than   a single solar system yet containing millions or  billions of solar masses before long it was clear   only one theorized object was capable of being  so dense a black hole of incredible proportions   and this raised an interesting question if other  galaxies house gigantic black holes what about one   it wouldn't take long for people to start looking  the first indication we had at the star-swallowing   monster at the heart of our galaxy came in 1974  in a paper by bruce balak and robert l brown the   pair had discovered a seriously powerful radio  source initially given the incredibly unsexy name   galactic center compact radio source in 1982  though brown decided to rechristen his discovery   in atomic physics putting a little asterisk next  to a name indicates it's in a high-energy state   brown evidently thought this was pretty neat  because he decided to use it for his own   high-energy discovery taking the name of the  constellation it appeared in he called this   mysterious radio source sagittarius a asterix  or sagittarius a star now all humanity needed   to do was prove it was a black hole as we're  about to see this was easier said than done even though the odds were that sagittarius  a star was an enormous black hole scientists   couldn't actually prove it was anything more than  a weird bright object to actually figure out what   it was they'd need to overcome some incredible  technological hurdles hurdles that prevented   us from seeing into the core of our own galaxy  luckily leaping majestically over technological   hurdles is what science is really all about the  breakthrough was the creation of high resolution   infrared cameras prior to this the biggest issue  had been we can't actually see the center of our   galaxy with even the most powerful telescopes  there's just too much interstellar dust in the   way so much so that it absorbs 100 of the light  emitted on the visible spectrum infrared light   though leaks through not much just 10 percent  of what those stars clustered around sagittarius   a star give off for these awesome new cameras  though 10 was enough enough to start tracking   and making measurements of stars right near our  galactic core and what these measurements showed   was something massive lurking within the  constellation of sagittarius starting in the   early 2000s scientists were able to follow the  paths of stars like s2 as they whirled around   this invisible object figuring out their orbits  allowed us to figure out the gravitational pull of   whatever they were orbiting this meant we could  calculate its mass which gave us such an absurdly   high number that the only possible answers  were either a a supermassive black hole or b   your mum fast forward to 2020 and the nobel prize  in physics was jointly awarded to those scientists   who helped prove sagittarius a star must be a  black hole but just because we now know what   lies at the heart of our galaxy doesn't mean the  story is over the more we learn about our resident   supermassive black hole the more interesting the  future of science seems to become right now for   example scientists at the event horizon telescope  a project that links radio telescopes across the   planet to effectively make a one big ass telescope  are finally trying to capture an image of   sagittarius a star nor are they the only ones the  james webb space telescope will count among its   missions and attempt to peer into the heart of our  galaxy's core potentially the best shot we have   at understanding its unique properties in short  this is a pretty exciting time to be a black hole   scientist and as we learn more about sagittarius  a star we might uncover all manner of other things   about our universe for instance just last year  scientific american reported on research by avi   loeb and manasvi lingam that suggests sagittarius  a star's dangerous belches may have hindered   life's developments on earth potentially wiping  out any complex life-forms for billions of years   until our star at last moved far enough away it's  still an unproven theory but it does show how much   more we might discover as our understanding of  the leviathan in our galaxy grows as we wrap up   this video then we do so potentially on the  brink of some incredible discoveries from a   weird signal detected by a guy working for the  telephone company sagittarius a star has evolved   into what we know it is today a monster of a black  hole spinning at the very heart of the milky way   and if our understanding can change so much in  90 years who knows what breakthroughs the next   century will bring because make no mistake there  is a lot to learn about our local supermassive   black hole stuff that makes even trained  astrophysicists giddy to think about if there's   one thing we're sure of it's that it's going to  be exciting as heck watching them figure it out i hope you found today's video interesting if  you did please do hit that like button below   don't forget to subscribe  and thank you for watching you

Channel: Geographics

Views: 423,101

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Id: SNOFs30P4sM

Length: 23min 53sec (1433 seconds)

Published: Wed Feb 23 2022