May 20, 2024

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Can we know the size of a supernova before it explodes?  |  Scientists answer  Sciences

Can we know the size of a supernova before it explodes? | Scientists answer Sciences

Talking about the size of supernovas is confusing, as they are not objects, but rather astronomical events: star explosions. There are two types based on the mechanism of their explosion: gravitational collapse, which is the most common, and thermonuclear collapse.

Thermonuclear supernovae occur if a white dwarf grabs enough mass from another star, causing its core to melt within seconds. White dwarfs are extremely dense objects that form when…

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Talking about the size of supernovas is confusing, as they are not objects, but rather astronomical events: star explosions. There are two types based on the mechanism of their explosion: gravitational collapse, which is the most common, and thermonuclear collapse.

Thermonuclear supernovae occur if a white dwarf grabs enough mass from another star, causing its core to melt within seconds. White dwarfs are very dense objects that form when a star with a mass less than eight times the mass of the Sun burns up all of its fuel. For example, our Sun will eventually become a white dwarf. These stellar remnants have a diameter of about 1% of the Sun's diameter and a mass similar to that of the Sun. In many cases, they are found in binary systems, close to another star from which they can take mass. When a white dwarf picks up mass from another star, there may come a time when, under certain conditions, its core melts in seconds and causes a shock wave that destroys the star. The luminosity of the white dwarf, which was very small due to the lack of nuclear reactions inside it, increases 100 billion times. These types of supernova are the ones that emit the most light because the star has been completely destroyed.

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Gravitational collapse supernovae occur when an extremely massive star (its mass equal to or greater than eight times the mass of the Sun) ends the life. At the end of their lives, these stars have an iron core surrounded by outer layers of lighter elements. At that moment, the star does not have enough energy to melt the iron, the balance between the pressure generated by nuclear reactions (outward) and the gravitational pressure (inward) is broken, the core contracts and the outer layers at the top fall. Star center. This causes the nucleus to become very hot and the iron atoms begin to break apart, creating a large number of neutrons. The core becomes increasingly hotter and more disintegration occurs until all the iron disintegrates in less than a second and the core collapses. What's left is a stellar nucleus consisting mainly of neutrons that emit a large number of neutrinos, which are very light elementary particles. These particles extract a huge amount of energy from the star, cooling it. The collapse ends when the neutron density is large enough for the neutrons to repel each other to stop the collapse. What remains is a neutron nucleus with a radius of between 10 and 20 kilometers.

Answering your question, this would be the first size to mention. This nucleus is what we call a neutron star. The size of that nucleus can be estimated using theoretical models. There is another option for the fate of this type of supernova, which is the formation of a black hole. If the mass of the nucleus is large enough, neutrons will not be able to stop the collapse, and instead of forming a neutron star, a black hole will be born. Due to the uncertainty in our theoretical models, the exact limit on the fundamental mass required to form a black hole instead of a neutron star is not completely known. In addition to giving rise to a neutron star or a black hole, supernovae that collapse due to gravity, such as thermonuclear supernovae, expel material at tremendous speeds. When the outer layers fall on the core, they bounce and create a pressure wave that expels it.

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If your question refers more to the extent of the supernova shock wave after the explosion, then here we can also make approximate calculations, although accuracy is difficult because we usually do not have precise data on the mass of the progenitor for example. The star or what exactly is around it. In addition, we must take into account our lack of understanding of some of the processes that occur during and after the explosion.

As I mentioned, the supernova explosion causes the outer layers of the star to be expelled by shock waves. This stellar remnant ends up dissolving into space after millions of years. Before that, there is a period of about 400 years during which the star's material expands freely at a speed of 10,000 kilometers per second until the wave front sweeps away a large enough amount of interstellar material, equal to the mass of the star's layers in that wave front. When this happens, expansion begins to slow. In that time, the matter has traveled about 10 light-years (one light-year is equivalent to 10 billion kilometers).

Then, the speed of expansion decreases as more and more material is pulled out without losing much energy. This ends after about 100,000 years. Up to this point, the shock wave has been emitting energy in different bands of the electromagnetic spectrum (which can be observed with our telescopes). This phase ends when the wave front begins to emit enough light to lose energy, causing it to cool for 1 million to 10 million years after the explosion. After that, the remnant stops expanding and dissolves in the interstellar medium. Until then it had traveled about 300 light-years.

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Marina Cermeno Gavilan She holds a PhD in theoretical physics and is a researcher at the Institute of Theoretical Physics of Madrid UAM-CSIC.

The question was sent via email by Angel Leno Biogar.

Formatting and writing: Victoria Toro.

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