Welcome back, everyone. So in our last lecture we talked about Supernova Type 1a, which were, are an amazing means of being able to get distances to very large distances. And we just want to talk a little bit more about this to sort of fill in some of the details. So, Supernova Type 1a are supernova that occur in binary systems, when there's two stars orbiting each other. And they always occur when mass is being drawn off of one of the stars, and being pulled onto the second star, when that second star is a white dwarf. Now, to understand this, let's just go back a little bit to understand what nova are. Because, of course, super nova are a example of nova on steroids. And nova were known about for quite some time. And they are also binary stars where we have a a mass donor star and a mass accretor star. And a accretor, again, is a white dwarf. And what happens is as mass goes from the first star to the second star it ends up falling on to the white dwarf and as material piles up onto the white dwarf, the pressures and densities can become so high that, basically, that material on the surface begins to fuse. You get a nuclear fusion occurring on the surface. And so, the star will brighten enormously as this wave of nuclear fusion runs around the surface of the star. And when that happens, the star the, the binary system brightens enormously. But that material, what happens is it basically is blow off the surface of the white dwarf and the whole system can start again. It can then, the mask can be taken from the second the first star again, dumped on to the white dwarf and so you get recurrent or common phenomena. So nova will occur over and over again. With Supernova Type 1a, the situation is slightly different well, not slightly different, but actually quite a bit different because of one fact. In a Type 1a Supernova, you get so much mass being dumped onto the second star, the white dwarf, that once nuclear burning begins it basically runs through the entire star. You're able to get the entire white dwarf begin nuclear burning. Meaning the carbon, the inert material, what once was the carbon in the, the core of the white dwarf. And then what happens is the star blows itself up. It's, it's a giant thermonuclear bomb, if you want to think about it. And the star is, is destroyed. And so, this is a type of supernova that's very different from the, the type, the core collapse supernova that we discussed in the last series of lectures, where basically a massive star just implodes in on itself. Now the interesting thing is that we talked about in just the last lecture was that because of the physics, the mechanisms by which this white dwarf blows up, the light curve, this is the, the, the, the change in brightness of the supernova over time is very standardized. And astronomers have learned how to use the way that the light diminishes in time to tell what the intrinsic brightness of the type 1 supernova, type 1a supernova was. And in that sense, the light curve becomes the label, 100 watts or whatever that astronomers can use to understand the intrinsic energy output of the type 1a supernova. And then compare that with how bright it actually appears to us and in that way we can see we can get distances. Any object any galaxy that has a type 1a supernova going off in it, we can get it's distance even if that galaxy is half way across the known universe. So the supernova type 1a are our best way of getting very exact distances to objects that are enormous distances away. Okay, with that information let us move on to talk about galaxies a little bit more. [BLANK_AUDIO]
