Tech UPTechnologyThis is how we would see the Sun if...

This is how we would see the Sun if our eyes could see neutrinos

In our head, halfway up, we have two fantastic particle detectors: our eyes . Specifically, they are capable of detecting photons , which are nothing more than the particles that make up light. However, they are not able to detect any type of photon, only those that have an energy within a very small range , what we call the “visible part of the electromagnetic spectrum” or simply “visible light”. In addition to this visible part there are, of course, two invisible parts. The one that includes photons with more energy than visible light and the one corresponding to photons with less energy.

These photon detectors that are our eyes help us circulate around the world (although they are not strictly necessary for this) and perceive what surrounds us. Of course , most of the photons that we end up detecting have their origin in the Sun. But the Sun not only emits photons, light, but also other particles. On the one hand, the solar wind , made up of charged particles (mainly electrons and protons), and on the other, it emits huge amounts of neutrinos . These particles are especially difficult to detect, but despite this, the Sun emits so many of them, that we have been able to photograph it (or rather neutrinograph it) using only these particles , obtaining something like this.

Seen in this way, this image of the Sun would not seem to be a great milestone , since it does not allow us to distinguish any obvious feature and also does not have much photographic quality. Nothing could be further from the truth. This photo is capable of giving us an amazing amount of information , although to explain it to you before we need to clarify a couple of points.

First of all: what are neutrinos and why is it so difficult to detect them? Neutrinos are subatomic particles that only interact through weak nuclear and gravitational interactions . Gravitational because nothing escapes its influence, but weak and only weak because it has no electric charge or color charge (which is what is affected by the strong nuclear interaction). This weak nuclear interaction has a very small range . That is, its intensity decreases very quickly with distance. So much so that it is barely effective for distances similar to the size of a proton , or on the order of a billionth of a meter ( 10-15 m). This has the consequence that trillions of neutrinos coming from the Sun are able to cross the Earth every second without interacting with any of the particles (mainly electrons, protons and neutrons) that make it up. It also implies that any neutrino is capable of passing through a block of lead one light year thick with only a 50% chance of hitting any of its atoms.

However, even though it is so unlikely that they interact with something and, consequently, are detected, the number of neutrinos that reaches us is so enormous that some of them end up interacting and an even smaller percentage, being detected . The question now therefore would be: How is the Sun capable of producing trillions of neutrinos per second?

These particles are produced during the different nuclear fusion processes that keep the star going and make it shine. For example , during the fusion of four hydrogen nuclei (each made up of one proton) to give rise to a helium nucleus (made up of two protons and two neutrons) , two very energetic neutrinos are emitted . These neutrinos are produced as a consequence of the different conservation laws that affect all fundamental particles.

When two protons fuse and one of them is transformed into a neutron in the process, certain particles are emitted that “counteract” the changes in the nature of these particles . For example, electric charge must be conserved , so a positron, which has a positive electric charge, like the original proton, will also be emitted . In addition , the lepton charge must be conserved, also emitting a neutrino .

Given then the incredible amounts of hydrogen that are transformed into helium every second, it is not surprising that so many neutrinos are emitted from the Sun. But what is so special about these neutrinos? As we have mentioned before, these particles are capable of passing through matter without being hardly affected. This will mean that they will also be able to pass through the Sun itself without flinching . It is in the core of the star where nuclear fusion processes take place and therefore where the mentioned neutrinos and other particles are produced.

It is estimated that a photon produced in this central region will take , after countless collisions and re-emissions, on the order of one hundred thousand years to reach the surface of the Sun. However, a neutrino , which will travel at almost the speed of light and will not be stopped by anything, will leave the Sun in just two seconds . Therefore, the photo exposed above, even though it is of poorer quality than those taken with conventional telescopes, will be a direct photo of the core of the star.

Thanks to images like this we can study this region that would be inaccessible by any other method and, in the process, test our models of star formation and evolution. Neutrino astronomy is a relatively recent field within astronomy, but it has already given incredible results, allowing for example to observe supernovae through their emission in neutrinos. In the future, if our detectors improve enough, we may be able to detect the very neutrinos that decoupled from the rest of the universe after their first second of life , following the Big Bang.


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