sometimes the star or the bright object that we look at in the night sky is so far away that all it looks like to our naked eyes even with our telescope it's just like a cloud so i'm just going to show you something let's zoom in so you can see the crab nebula here okay and what we see here is basically nebula which means cloud interstellar cloud agreed okay so the greeks were the first people who look up at the sky and started naming things and we followed their names so this crap nebula is what we call a supernova remnant okay so supernova remnant means once upon a time long time ago there was a star here and this star went through the life cycles and it exploded okay so massive stars or star with very large mass will explode at the end of their life cycle and the explosion kind of look like this so it starts off like this and booms so i want you to pay attention to this gif of a supernova explosion okay so what we have is a star that's at the end of its life cycle it will expand a bit and then it explodes expand a bit then explodes okay so at the end of this explosion we get what we call a nebula or supernova remnant which is your nebula this one okay so our left are just interstellar dust and clouds just you know floating around in space and in the middle here there is a neutron star okay so if you've learned the life cycles of stars you will know that this will happen but one very interesting thing about this supernova explosion is that there is a boom sudden increase in intensity now although we may not be able to pick up the individual stars because you know they're kind of too far away you can't really tell you know when i zoom in and look at something that is really far let's say i you know go back out and look for stuff this thing is actually like can't really see and the further the object is the more grainy you know or the harder it is to tell when we look up into the night sky it won't look as distinct as the bright dots that we will expect from a siphoid variable so which means we need to use a different method or a different standard candle and ladies and gentlemen this supernova explosion this is our another type of standard candle we are going to use its peak luminosity so when this luminosity peaks and that light begin to shoot through space and travel towards earth using the inverse square law we can also calculate values like distances of this supernova explosion to our planet all right so let's check it out in our notes all right so at very large distance we cannot see individual stars right so because they're too far away so see feed variable cannot be used as standard candles for further galaxies cannot too far away a supernova as mentioned i'll show you just now is a star that suddenly and very rapidly increases luminosity okay so basically it's at the end of its life cycle generally that's when supernova explosion will occur so very rapidly increases its luminosity because of an explosion that ejects most of its mass away so basically it's an explosion and when you see and you look at the nebula nebula which is the interstellar cloud okay that cloud is basically what is remain of a supernova explosion okay so when we think about supernova right what we care about is the sudden increase in luminosity okay and type 1a of course there are different classifications for supernova but we're going to focus on this particular type okay because we use it as a standard candle all right so this type 1a is so bright when they explode that they can be seen in distant galaxies and then dim over a period of days and months and so that light shines so bright that even after the sun dies and then nothing is left but the remnants and the nebula clouds the light is still traveling in space isn't that quite poetic okay so if you look at this light curve you can see zero let's say day zero is when the super the supernova explosion occurs you notice that the intensity is really bright okay when they say luminosity per solar unit is is you know more than 10 to the power nine times the like the brightness of the star you look at the sky and look at how bright the star is i mean the sun is this is solar units so it's how many times brighter than the sun okay so the type 1a supernova explosion occurs with the same from the same mass of stars because if you remember from the star life cycle different masses will have different kind of life cycle small stars something else will happen to them this is about a medium-sized star the supernova okay and then very massive stars will form black holes very interesting stuff right but that's not covered in our a level content so you just need to know that type 1a supernova or any kind supernova occurs for the same mass of star which means they will all have nearly the same luminosity at the peak of their outbursts so what we care about is the brightness of the stars that we can see because to be honest we there's no way to reliably use orbital mechanics or what we study in gravitational fields to calculate any meaningful data from a star that's so far away right okay so what we'll probably do is we can look at the electromagnetic radiation you know the light the em radiation that reaches earth okay so basically what we're trying to say here is same mass will have the same uh light curve because same mass will have the same type 1a supernova explosion all right so light cuff will look uh the light curve will look like this you can see that um it will reach a peak at its maximum so think back about the diagram that i've sort of shown you just now this one here okay so the peak is here and then it explode so it's a bit like this is why it's happening whoops it explodes okay it explodes so here is when the explosion happened so the intensity increases very rapidly this is already 10 to the power of 7 let me zoom in a bit this is already 10 to the power 7. so it's more than 1 million times brighter than our good old sun so it will just suddenly shine very hot and white and bright that explode okay so this is what is going on and then with time that intensity the star will slowly cool down whatever that's left of the star all right so this is basically using a different idea to measure uh luminosity and using luminosity to determine distance all right so let's look at it an example a short one okay so a type 1a supernova is observed in another galaxy with peak so all we care about is the peak peak radiant flux intensity of 9 times 10 to the power of 8 negative 18 what meter negative 2. teacher you say is bright or but then why is this value so small well this value is kind of small because the star is really really really really far away so using the inverse square log no matter how bright you are if you're super far away we can't really see how bright the star actually is even if it's a supernova explosion okay if we assume that the peak luminosity of type 1a is about 10 to the power of 6 watt estimate the distance of this galaxy from earth and we can't even tell how long ago did this explosion happen was it yesterday okay and we are given uh the value of one light year okay in meters all right let's try to figure out this question so this is our star okay and we assume that the peak luminosity which is 10 to the power of 36 occurs at the star then the maximum intensity or the pulse will begin to travel or make its way towards earth or rather the observer okay so maybe this is earth's observing control the eye here to observe this one so by the time this light actually travels here okay you know your light wave the radiant flux intensity measured here is 9 times 10 to the power of negative 18 watt per meter square okay so this peak this peak luminosity l by the time it reaches our earth we will observe the peak as this much so we can still use the inverse square law okay which is radiant flux intensity is equal to l over 4 pi d squared okay luminosity over area so i guess we can substitute the value f times 10 to the power negative 18 is equal to 10 to the power of 36 over 4 pi d squared okay i'm going to check in on my calculator so my calculator tells me once i solve for d that d will be equal to 9.4 times 10 to the power of 25 meter but they did say estimate so when they say estimate i'll try to keep my answer to 1 sf so 9 times 10 to the power of 25 meter because sticking to one sig fig right this is part a so at the end of the day right we are just looking at the peak the peak can easily be detected so by the time it reaches earth okay or reaches the observer we can use the inverse inverse square relationship because all type 1a supernova has a peak of around 10 to the power of 36 what okay next how long ago did this explode well one light year this uh 9.46 times 10 to the power of 15 this one gives us the distance traveled by light in one unit hence lightning okay so i guess we could use the simple equation of uh you know 9 times 10 to the power of 25 divided by 9.46 times 10 to the power of 15 this will give me around 10 to the power of 10 right because you know 9 by nine point four five we are still estimating by the way nine point four six so zero point nine five okay so it was around ten ten to the power of ten light years which means the supernova exploded or the sun exploded 10 to the power of 10 like 10 up to about 10 years ago quite long right yes so this is what it's like it's very mind-boggling because it's so far away right so although it exploded 10 to the power of 10 years ago which is like come on that's ten zeros okay like our human brain cannot understand one okay this is about like what ten ten billion right okay so this is our wonderful universe at this scale things are quite amazing all right so just as a recap what we're looking for is the peak radiant flux intensity so during the explosion the light is actually 10 to the power of 36 by the time it reaches us it is 9 times 10 to the power negative 18 watt per meter squared so we can place the luminosity 10 to the power 36 and also the detected radiant flux intensity of this peak into the equation and we can find the distance okay with that distance we can actually divide by one light year to find the number of years the light has taken to travel to us and it is 10 billion years meaning this explosion occurred 10 billion years ago so in a nutshell your type 1a supernova is a class of supernova that talks about the explosion of stars during the explosion the stars will suddenly create a pulse of very large intense luminosity or intensity okay so this very large luminosity is a burst of light and that burst of light would travel across space and universe and after 1 billion years 10 billion years it arrived on the earthbound observer and the earth observable stare at the brightness tala so we can use this to estimate distances as well all these are just estimations okay so this is more suitable for stars or galaxies or bright objects that are really really far away so far away that we can't even tell the individual stars apart so what we're picking up is just the sudden peak sudden peak in luminosity or brightness all right okay that's it for this one see you in the next video