Type II supernova

A Type II supernova is a powerful explosion that happens when a very big star runs out of energy and collapses quickly. For a star to explode this way, it must be at least 8 but no more than 40 to 50 times heavier than the mass of the Sun. These explosions are special because they show hydrogen in their light, which helps scientists identify them. We usually see them in the spinning parts of galaxies and in areas full of young, massive stars, but not in round galaxies made mostly of older stars.

Big stars shine by mixing together smaller parts of atoms in a process called nuclear fusion. Unlike our Sun, these massive stars can mix heavier elements, but this takes very high temperatures and pressures, so they live shorter lives. They keep mixing heavier and heavier elements until they make a core of iron and nickel. Mixing iron or nickel does not give off energy, so the core can no longer stay stable and starts to collapse under its own weight.

When the collapsing core gets heavier than a certain limit, it crushes inward very fast. This creates huge temperatures and forms particles called neutrons and neutrinos. The collapse stops suddenly, sending a powerful wave outward that blows the star apart in a bright explosion. What is left behind can become either a neutron star or a black hole, depending on how heavy the original star was. These explosions help create some of the heaviest elements in the universe.

Formation

Stars that are much bigger than the Sun go through many changes during their lives. In the center of a star, tiny particles called hydrogen come together to make helium. This process gives off heat that keeps the star from falling apart. As time goes on, the helium builds up in the center of the star.

When the hydrogen runs out, the center of the star starts to shrink. This makes it hotter, and the helium can start making new particles called carbon and oxygen.

Very big stars can keep changing their centers in this way, making heavier and heavier particles until something amazing happens.

Core collapse

When a big star runs out of fuel, its center collapses very quickly. This happens because the star can no longer create energy by combining atoms. The collapse happens so fast that it creates huge amounts of energy. This energy causes the star to explode in what we call a supernova.

In a Type II supernova, the explosion happens because the core of the star collapses and then rebounds. This creates a wave that pushes the outer parts of the star away. The explosion releases a lot of energy, mostly in a type of particle called a neutrino. If the star is not too heavy, what is left after the explosion is a tiny, very dense object called a neutron star. If the star is heavier, it might form a black hole instead.

Theoretical models

The Standard Model of particle physics helps us understand how tiny parts of things, called elementary particles, work together. It can tell us what happens to these particles in a supernova, a huge explosion of a star. Even though the energy per particle in a supernova is small, the conditions inside can be very dense, which might change how particles normally behave.

One big question scientists still have is how the burst of neutrinos gives enough energy to make the star explode. Only a tiny bit of this energy needs to be moved to the rest of the star, but it’s hard to explain exactly how this happens. Some ideas suggest that movements inside the star, called convective overturn, help finish the explosion. During this explosion, heavier elements are created, and the explosion sends out gas and dust that contains these heavier elements.

Understanding how neutrino physics and the movements of the star’s material work together is key to solving these mysteries. Some models also look at special patterns in the stalled shock wave that might help restart it. Scientists use computer models to predict what happens after the explosion starts, including what elements are made and how bright the supernova will appear.

Light curves for Type II-L and Type II-P supernovae

When scientists look at the light from a Type II supernova, they often see special patterns that show hydrogen is present. This helps them tell Type II supernovae apart from other kinds.

The brightness of a Type II supernova changes over time in a special way. It gets brighter until it reaches a peak, then it starts to dim. There are two main types based on how the brightness changes. One type, called Type II-L, dims steadily after reaching its peak. The other type, called Type II-P, has a part where the brightness stays almost the same for a while before continuing to dim. This difference happens because of how the outer parts of the exploding star behave.

Type IIn supernovae

The "n" stands for narrow, meaning these supernovae show thin lines of a certain element in their light. This happens when the explosion pushes into gas around the star. Scientists think these stars lose a lot of material before they explode.

Some of these supernovae heat up dust around them, making them glow especially bright in a certain kind of light. This glow can last a very long time. These special supernovae are named after one famous example. They were found using special space telescopes.

Type IIb supernovae

A Type IIb supernova has a small amount of hydrogen in its early light, which is why it is called a Type II. But later, the hydrogen disappears, and its light pattern starts to look more like a Type Ib supernova. This kind of supernova may come from a big star that lost most of its outer layers, or from a star that lost its hydrogen because of a nearby star in a pair. As the material from the explosion spreads out, the hydrogen fades away, showing the layers inside. A well-known example of a Type IIb supernova is SN 1993J, and another example is Cassiopeia A. The idea of a Type IIb supernova was first suggested in 1987.