galaxies

We tend to think about the stars as what we see: millions of bright dots that appear every night above our heads. However, what lies behind it is much bigger. We see light that was emitted dozens or even hundreds of years ago, coming from immense celestial objects, inside which reactions more energetic than any chemical reaction are taking place. And it is not about chemistry, but about something much more intense: nuclear fusion. The “fire” that we see from Earth is the fruit of this fusion, but there comes a time when there is no longer any fuel. With no more fuel to add to the bonfire, the star collapses and dies. This death can be cold and silent, as happens with the smallest stars, but it can also be explosive and colossal when it comes to the largest stars. After that explosion, known as supernovaa black hole or a neutron stardepends on the size of the star that died. The supernova explosion is one of the largest that occurs in the Universe. It is estimated that it releases energy equivalent to 1030 times that of the Hiroshima bomb. It is a phenomenon that releases so much radiation that even has become related with two of the five great mass extinctions that have taken place on Earth. But what makes the death of a star end up becoming something so huge? To know, we must start at the beginning. What is a supernova? A supernova is the last death of a star with a mass at least eight times that of our Sun. When runs out of fuel to continue maintaining the nuclear fusion running, it collapses, releasing a lot of energy. But this is not something that happens quickly. A massive star goes through several phases before reaching the point of generating a supernova. How is a supernova formed? Nuclear fusion is a reaction in which the nuclei of two light atoms fuse to form a heavier onewith a great release of energy. In the case of stars, this process is essential to keep them “on” during the early stages of their life, since They fuse hydrogen nuclei and transform them into helium. It occurs in all stars, although it occurs much more quickly in larger ones. While nuclear fusion occurs in the nucleus, there are two forces that remain in balance. On the one hand, gravity, which pushes all the material inward. And, on the other hand, the radiation pressure, which is generated by the effect of fusion in the stellar core and pushes outward. This occurs unchanged until the time comes when that hydrogen runs out. When spent in the core, the forces are no longer in balance. Gravity overcomes radiation pressure, so the core is pushed inward and compressed. It heats up so much that the helium that remained in the core also acquires the ability to fuse, becoming a new fuelwhich will be transformed into carbon and oxygen. But there was not only hydrogen in the core of the star. This element is also found in its outermost layers, with the difference that it remains inactive. Does not merge. Or, actually, it doesn’t at first. When this first compression occurs, with the consequent stellar heating, the outer hydrogen begins to fuse, causing the growth of the star, which becomes a red giant. Unlike smaller stars, those with a lot of mass have enough energy so they can continue fusing other atoms beyond helium. Carbon, for example, fuses to give rise to neon and magnesium. Neon does the same, generating oxygen and magnesium. That oxygen fuses to produce silicon and sulfur and, finally, the silicon atoms fuse very quickly, generating an iron nucleus. Here comes a key point, since Iron is the most stable element of all those producedso the fusion is slowed down. Cores cannot continue to merge. It is now impossible to continue generating energy and the gravity we talked about at the beginning completely defeats the star. As a result, the core collapses on itself until reaching a limit where a large shock wave is generated and the outer layers collapse, which are violently released into space. We are facing a supernova, an explosion that can last from weeks to months or years. In reality, this explosion can also occur in a binary star systemwhen one steals material from another. Therefore, when we talk about supernovas we must differentiate several types. Types of supernovae All we have seen so far is the description of the most common supernovae. Nevertheless, there are other types of supernovaewhich differ both in the nature of their parent star and in the mechanism by which the explosion takes place. Mainly, The differences are seen when analyzing their spectrum. That is, the light they absorb or emit. This is a process used to determine chemical compositions, as different elements absorb or emit light in very specific patterns of wavelengths. Type I supernova: Hydrogen is not identified in its spectrum. Type Ia: They do not have hydrogen or helium, but they do have a strong line of silicon. This indicates that they are produced by a thermonuclear explosion in a binary system, when a white dwarf accumulates additional material from a companion star. Type Ib: The spectrum does not have hydrogen, but it does have helium. It is the classic supernova that we have talked about so far. The one generated as a remnant of a neutron star or a black hole after the collapse of a large star. Typically more than 8 solar masses. It does not have hydrogen, because the outer layers of the star that contained it were lost. On the other hand, those of helium were preserved. Type IC: There is no hydrogen or helium in the spectrum. In this case, we are also facing an explosion like the one we have described so far. The only difference with type Ib is that, during the explosion, its outer layers are stripped of both hydrogen … Read more