Betelgeuse Explained

[Music] one of the closest massive stars to the Sun is acting weird Betelgeuse recently dimmed down to just one third of his usual brightness what could be causing this irregular behavior could this mean that it's about to explode grab a cup of tea and settle in because today we're going to be taking a deep dive into everything happening with the enigmatic Betelgeuse Beetlejuice lucky' towards the Orion constellation and you'll find this infamous star at the shoulder of the mythological hunter also known as alpha Orionis it's easy to spot being the 10th brightest star in the sky at least usually it's the tenth brightest you see over the last few months astronomers have noticed something strange about this star it's now about 1/3 as bright as usual something noticeable by eye in fact it's now been demoted to the 24th brightest star to understand what's happening we first have to talk about some background about this star because you see what makes this dimming particularly interesting is that Betelgeuse is no ordinary star no in fact for example it is far far younger than our own Sun whilst the Sun was born from the gravitational collapse of an ancient giant molecular cloud some four thousand six hundred million years ago Betelgeuse was probably born just 10 million years ago for some context this would be about the time that our hominid ancestors started to splinter off from what would become gorillas if we spread the sun's age out over a calendar of 365 days Betelgeuse would have been born on December 31st at 5 a.m. it's so damn young that rocky planets like the earth would likely not have had enough time to her formed yet and frankly likely never will so Betelgeuse is a very young star but in another sense it's actually an old star at least when we compare it to how long this star is expected to survive so let's compare it to the Sun the Sun can be thought of as middle-aged enough fuel to last for another five billion years before eventually evolving into a short-lived giant phase and then finally leaving behind a dead white dwarf Betelgeuse on the other hand is running on empty and it has in fact already transformed into its giant phase you see Betelgeuse has been very greedy during its short life time it was born with a whopping 15 times more mass than our own Sun and ever since it got going it's just been feasting through its fuel supply like a bat out of hell the star is a monster it spews out 100,000 times more power than our own Sun does and even before becoming a giant during its main sequence lifetime that the Sun currently enjoys it still even then would have been spewing out tens of thousands of times more power than our own Sun you've probably heard the expression the candle that burns twice as hot lasts half as long well here we'd say that the star that burns 10,000 times as bright lasts 1,000 times less long although admittedly we are talking about a star that began its life with at least 10 times as much candle wax in the first place massive stars like Betelgeuse are actually very rare just like animals most develop into a fairly average size for their species but really you get a freakish set of circumstances that somehow result in a giant iced example and these giants really stand out in the same way Betelgeuse is a freak because only 1 in 200 stars will be born with as much mass inside them as Betelgeuse was and not only is Betelgeuse massive the fact that it's enter disjoint phase means it's also humongous to understand this gargantuan term let's look inside a star a star has two key zones the core where fusion happens and the envelope which is basically just hot gas sat on top as stars fuse hydrogen into denser helium inside their cause they accumulate an inert inner core of helium ash inside their centers now because helium is denser than hydrogen the core contracts which in turn causes it to heat up eventually the central temperature and pressure become extreme enough that helium can now fuse into carbon via the triple alpha process which substantially increases the energy output of the core and this in turn causes the outer envelope of non fusing hydrogen to simply puff up a bit like a hot air balloon except that that balloon has now puffed up to the size of Jupiter's orbit around the Sun a gargantuan size so this broadly describes what's happening inside Betelgeuse right now my it is as big as it is but it will not stay in this state forever because as it's accumulating now carbon ash inside its core that temperature and pressure will continue to rise in the center eventually even the carbon and heavier elements still will be able to start fusing and once this happens well the end is nigh for beetle we'll be looking at a few hundred years perhaps a couple of millennia until its demise what happens to massive stars like Betelgeuse when they die there are two likely possibilities the one you are probably hearing the most about is a supernova remember that the core will eventually start to fuse carbon and even heavier elements in its center but once it starts producing iron ash well the gig is up that's because fusing things heavier than iron is what we would call an endothermic reaction and all that means is that you actually have to put in more energy to conduct the reaction than you get out the other end in other words this reaction saps energy from the core remember that this is a massive star and so it has a huge self gravity trying to collapse it in on itself when the heat source starts to dwindle due to the accumulation of this iron ash well there's nothing to resist that gravitational collapse anymore and so the star literally falls in on itself imploding it's at this point that the two possible futures for Betelgeuse diverge one is going to be a band and the other is a whimper as this wave of infalling material the outer envelope of the star falls in towards the core due to gravity one of two things is going to happen either the core is gonna structurally resist that in falling wave and notice or bounce off the outside or the core will not be up to resist and it will simply crush down stars on the lighter end of the massive star spectrum around ten times the sun's mass will not generate enough pressure to collapse the inner core instead they'll merely compress it into a super dense neutron star state and then bounce off that neutronic interior that bounce back leads to a giant shock wave that propagates out into space releasing tremendous waves of energy and spewing matter across the void and that's what we call a supernova or to be a little bit more technical a core collapse supernova but what if this star is heavier than ten times the sun's mass well now there is a lot more material falling down onto that inner core so much so that it can actually overwhelm even the resistive strength of neutronic matter and so the star will fall in crushing the core in fact it will fall all the way in all the way in to a singular point of infinite density a black hole in some cases the bounce-back still happens it forms a neutron star but some of that wave of bouncing out material ends up falling back onto the neutron star and it just tips the balance enough to turn that neutron star into a black hole all the same but in other cases there is so much in falling material that the star just literally implodes it winks out of existence there's no bounce-back there's no stooping over there's no bang of any kind it just disappears this winking out has in fact been seen before around 2010 astronomers witnessed another red supergiant in the galaxy NGC 6-9 46 simply disappear this actually wasn't even noticed at the time and it was only later that a couple of astronomers at a higher state university checked carefully through the archival data and found this remarkable event now that star was likely born with around 25 times more mass than the Sun as shown here but lower mass red supergiant's in the range of sort of ten to fifteen times the mass of the Sun have been seen to do the opposite and explode now if we compare these observations to theoretical more it matches up quite nicely here you can see a prediction for whether the star will implode into a black hole winking out or turn into a supernova in green and this clearly depends on the stars mass the outcome of these models shows some randomness the rotation speed metallicity and intrinsically stochastic nature of the stars interior means that we can't always predict exactly what will happen based on a star's mass alone and so this is why in part it's so difficult to say exactly what will happen to Betelgeuse this situation is exacerbated by the fact we actually don't know the mass of Betelgeuse and certainly not the mass of Betelgeuse it was born with and very well and that's because in turn we don't even know a precise distance for Betelgeuse and so in turn this means that we end up with a very large uncertainty on its mass so comparing to the theoretical models one can see how it's certainly possible that Betelgeuse might just disappear one day without a bank okay so with this fascinating background about these massive stars out of the way we can now finally talk about what has been happening with Betelgeuse over the last few months the first thing to say is that Betelgeuse is a variable star I mean it is not surprising for his brightness to change it's not a light bulb it's brightness changes by a few percent even ten percent quite often and has been seen for decades now what's really unusual about what's been happening lately is that this is a fairly constant and steep regular decline in brightness which has gone really quite deep down to one third of its usual brightness and that is frankly kind of weird I want to emphasize that that number represents the minimum in the stars a recent episode of dimming in the last couple of weeks it has actually started to stabilize and even reverse brightening back up again the story gets extra-spicy when we throw in these two images of the star taken about a year apart now normally it's impossible to resolve individual stars like this but some supergiant's are so big that we can at least get a fuzzy image like this one clearly Betelgeuse looks quite different between these two photos and that fact combined with the dimming has a lot of folks quite worried so let's just ask the obvious question that song everybody's lips right now and that is does this dimming of Betelgeuse mean that it's about to go supernova sure answer probably not and there's a few reasons for this first off we really don't have any clear prediction that stars are expected to undergo a period of dimming before going supernova the hydro dynamics of these stellar interiors is very complicated and there's a intricate feedback with gravity waves that actually affects their luminosity output in a fairly unpredictable way here's an example of a prediction for the luminosity of a star essentially how bright is versus its surface temperature in the final years before its death from Professor Jim fuller the star's luminosity is indeed sometimes dimming but it is also often brightening - I mean it's really all over the map we've never really caught a supernova in the act before at least in the days and years preceding the event and so we can't really tell you from data how stars behave just before they go supernova and so these models are really kind of the best we have right now and so frankly we just don't know how stars behave just before going supernova we don't know that it looks like what's happening right now now in that model prediction I showed you for the stars pre supernova behavior what's being shown here is the luminosity now it's tempting to say that this widely reported recent dimming translates directly to a decrease in luminosity but that's actually not true now these reported dimming that we've been hearing about have all been of the star's brightness in the visible light part of the spectrum but Betelgeuse like all stars produces radiation are all different wavelengths across the entire electromagnetic spectrum and so if we want to calculate luminosity we have to actually add up all of that rightness across the entire spectrum and that's not what we observed with these dimming it is not the luminosity of the star fortunately of course there is a way that we can get the luminosity we just simply have to do these observations at other parts of the spectrum apart from visible light and that's exactly what astronomers have very recently done infrared measurements taken at the O'Brien Observatory in Minnesota just last week showed that the star has the same brightness in the infrared as it did 50 years ago in other words this dimming does not represent a change in the star's overall power output it's just limited to the visible light part of the spectrum okay so maybe we can take our fingers off the panic button we don't seem to be in the regime of a wildly varying star like Jim fuller predictor but then how do we explain this pronounced a visible light dimming as well as the strange lopsided image that was recently captured [Music] there are broadly two popular theories to explain what's being going on with beetlejuice recently if we are willing to discount the supernova hypothesis just for the moment the first is a giant star spot if we look at the Sun we see small sunspots quite often these are regions where the sun's magnetic field lines temporarily come together in a way that inhibits convection of heat from the sun's interior up to its surface without that heat coming up to this part of the surface well that patch of the surface cools down it gets to about half of its usual temperature and that in turn means that it appears darker this is very much analogous to how if you pull a piece of iron out of a fire it will glow red initially but then cool down and stop growing now a spot or collection of spots that is big enough to block out about two-thirds of the stars usual brightness would have to therefore block out about two-thirds of the star's surface at least the hemisphere that we can see if the other hemisphere is spot free then this means that in total about 1/3 of the star surface would have to be covered in spots for the Sun spar certainly never get so big or so numerous as to block out anywhere near this much of the surface other giant stars have been recorded to do this in the past for example the orange giant HD one two five four five in a constellation Triangulum has had its surface resolved with a special technique called Doppler imaging that clearly reveals sparse covering about a quarter of the surface not quite a third but close enough to show us that this is at least a plausible explanation now for the sun spots come and go on a roughly 11-year cycle and at the peak of this cycle about 1% of the star surface is covered in spots which corresponds to a fairly marginal change in the luminosity of the star it actually only increases point zero seven percent and so stars luminosities are fairly robust to changes in their spot coverage when we combine all these points together we can kind of see how this spot hypothesis could work then for Betelgeuse we can explain the fact that luminosity doesn't seem to be changing very much we can explain the apparent dimming in the visible part of the spectrum and we can also explain that lopsided image all with a single hypothesis now on the Sun record that spots are caused by magnetic field lines impeding convection these spots are about the size of the earth typically but if we zoom in there's another effect at play here you can see a much finer grain effect each one of these little cells that you're looking at is about the size of Texas what's amazing is that this is real data from Dacus not a simulation of our Sun and here you can cleanly resolve the surface at incredible detail each little bubble that you can see is the top of a convection cell and is usually called a granule the variability you are seeing is usually called granulation caused by the convection of hot plasma beneath the surface a bit like a lava lamp the size of these granulation cells is directly related to the strength of surface gravity on these stars so for the Sun nice out of the size of Texas and the surface gravity is about 270 meters per second square something like 27 28 times earth gravity but for Betelgeuse because it's so puffed up the surface gravity is really pathetic it's just point zero zero three meters per second squared which is about three thousand times less than the gravity I'm currently feeling here on earth it's really quite ridiculous and so because the gravity is so weak on the surface of Betelgeuse then these granulation cell get really really big Beetlejuice doesn't like to do anything small there's some beautiful computer simulations of the convection cell behavior for such stars that I'm showing you here it reveals just how effervescent lively and bubbling the exterior envelope truly is now sadly we can't resolve the surface of Betelgeuse as precisely as this with existing telescopes so let's downgrade the animation to the sort of fuzziness that we'd see realistically in watching this you indeed see that granulation alone can produce very large dark features on the surface as well as creating lopsided images in individual frames so all in all I'd say that a fairly extreme episode of this natural convection behavior could be an explanation for what has been happening recently with Betelgeuse but I promised you two possible explanations and the other one is equally compelling now remember that I said that the surface gravity on Betelgeuse is pathetically weak and so that might make you wonder hey if I was stood on the surface of Betelgeuse could I jump off into space could I achieve escape velocity the escape velocity is given by the following equation where G is the surface gravity and R is the radius of the object for the Sun this gives about 600 kilometers per second so you're gonna need a lot of energy to ever leave the Sun surface on Betelgeuse though it's about ten times less just 60 kilometers per second and so this raises the possibility that a strong convulsion from within the Stars interior could have propagated out to the surface with enough force to have actually flung off the outer layer into deep space or at least a part of it and once that layer was dispatched from the star it would have cooled down and eventually ended up blocking out some of the star's light essentially it's just dust we even see some ever for previous episodes of dust released as you can see here in this real image now with the giant spot scenario the surface has actually cooled a little bit but here the surface is essentially the same temperature is just that there's some dust getting in the way and so recent work by astronomer Emily Levesque investigated what the temperature of the surface was using a spectral technique they found that the star surface doesn't appear consistent with an episode of dramatic cooling and so on this basis they favor the dust hypothesis and so this leaves us with two quite compelling explanations without the need to invoke a supernova now because there's so much we don't know about how stars behave in those final years before turning into a supernova then it is still absolutely possible that what we are seeing are the signs of an impending supernova but typically stars spend about a hundred thousand years in this phase of their life and so it's just probabilistically unlikely that that will coincide with our short human lifetimes it's also a shame because if Betelgeuse did go supernova it's 650 light years away which means it's far enough away that it won't hurt us but close enough that we would have the opportunity to study in great detail and learn so much about the final stages of this enigmatic type of star of course it would also put up a very nice light show outshining even the full moon of this peak brightness or it might just wink out leaving behind a black hole which would also be an incredible observation to see massive stars like Betelgeuse are amazing yes they are unusual rare beasts which are unlikely to ever form planets let alone life but on the other hand they are also somehow intimately connected to us that's because it's within these massive stellar engines that many of the heavy elements inside your body seems like phosphorus potassium oxygen were forged deep within its interior and when these stars came to their end they violently exploded these enriched guts across the cosmos those newly forged heavy elements were cast out across the galaxy to distant shores because there was so much hydrogen left and fused new smaller stars formed from the debris which in turn eventually formed planets enriched with these heavier elements crucial for life and those same elements are inside of your body right now they were at one point in their history inside the powers of one of the most massive stars in the universe you are in essence made of ash and so watching Betelgeuse is like getting to see one of the earliest steps in the origin of living things like looking into a mirror of our own beginnings these stars violently rip themselves apart in an almost sacrificial act so that complex chemical entities such as ourselves might one day be born rising like a phoenix fire flames [Music] [Music]

Channel: Cool Worlds

Views: 896,420

Rating: 4.8597093 out of 5

Keywords: Astronomy, Astrophysics, betelgeuse, betelgeuse explode, betelgeuse supernova, betelgeuse black hole, massive star death, betelgeuse dimming, betelgeuse weird, betelgeuse explained, black hole, failed supernova, betelgeuse latest, supernova nearby, will beteleguese, cool worlds, david kipping

Id: 5bvuwTuGnkc

Length: 28min 38sec (1718 seconds)

Published: Sat Feb 29 2020