I have long wondered about the sense of the shaky humor of the Universe. After all, how else could one of the most ethereal and ghostly particles in the cosmos be fundamentally responsible for some of the most colossal and violent explosions in it?
New research indicates that neutrinos not only play an important role in supernova explosions, but we need to realize all their characteristics to really understand why the stars explode.
Stars generate energy in their nuclei, fusing lighter elements into heavier ones. This is how a star prevents its own gravity from causing it to collapse; the heat generated inflates the star, creating a pressure that supports it.
The most massive stars take this process of producing energy to the extreme; While lower-mass stars, such as the Sun, stop after fusing helium into carbon and oxygen, massive stars continue to fuse elements to iron.
However, once the nucleus of a strong star is iron, a series of events take place that actually remove energy from the core, allowing gravity to dominate. The core collapses, creating a huge explosion of energy so huge that it blows the outer layers of the star, creating an explosion we call a supernova.
A crucial part of this event is the generation of an amazing number of neutrinos. These are subatomic particles, which, taken individually, are as insubstantial as the Universe does. They are so ugly to interact with normal matter that they can go through large amounts of material without notification; for them, the Earth itself is completely transparent and they travel through it as if it were not there at all.
But when the iron nucleus of a massive star collapses, neutrinos are created with such a large amount of energy that the material that falls just outside the core of the star actually absorbs a large number of them; it also helps that the material that rushes down is extraordinarily dense and able to capture so many.
The amount of energy that this wave of neutrinos vaporizing the soul gives to matter is enough to stop not only the collapse, but also towards this, sending octylons of tons of stellar matter exploding outward with an appreciable fraction of the speed of light.
The energy of a supernova even in visible light is so great that it can equal the production of an entire galaxy. However, this is only 1% of the total energy of the event; the vast majority of it is released in the form of energy neutrinos. This is how strong a role plays.
Before this was understood, theoretical astronomers had a difficult time obtaining the collapse of the nucleus to actually create the explosion. Simple physics models have shown that the star’s explosion will stop and that no supernova will occur. Over the years, as computers became more sophisticated, it was possible to complicate the equations introduced into the models, achieving a better reality. Once the neutrinos were added to the mixture, it became clear what key part they added.
The models are doing pretty well now, but there is always room for improvement. For example, we know that neutrinos come in three different types, called tastes: your neutrinos, electron and muon. We also know that under certain conditions the aromas oscillate, which means that one type of neutrino can change to another type. All three have different characteristics and interact differently with matter. How does this affect supernovae?
A team of scientists analyzed this. They created a very sophisticated computer model of a star’s core as it exploded, allowing neutrinos to not only change the flavor, but also interact with each other. When this happens, the flavor changes happen much faster, what they call a fast conversion.
What they found is that by including all three flavors and allowing them to interact and convert, the conditions inside the collapsing star core can change. For example, neutrinos cannot be emitted isotropically (in all directions), but have an angular distribution; may be emitted preferentially in some directions.
This can have a very different effect on the explosion than the assumption of istropism. We know that some supernova explosions are not symmetrical, taking place in the center or with explosive energy in one direction more than another. The amount of energy from the neutrino release is so great that even a slight asymmetry can give the nucleus a huge blow, sending the collapsed core (now a neutron star or a black hole) like a rocket.
The models used by scientists are a first step in understanding this effect and how big it could be. They showed that it is possible that the inclusion of all neutrino features may be important, but what happens in detail is yet to be determined.
However, this is interesting. When I was in high school, taking stellar interior physics classes, the latest generation models still had problems with the explosion of the stars. And now we have models that not only work, but begin to reveal previously unknown aspects of these events. Not only that, but we can turn this around, observe real supernovae in the sky and see what their explosions can tell us about the neutrinos themselves.
It’s funny: supernova explosions create a fair amount of matter you see around you: calcium in your bones, iron in your blood, the elements that make up life and air, rocks and just about anything. Neutrinos are essential for this creation, in a few moments giving birth to so much that we have to live. However, once realized, these particles ignore that matter, passing through it carelessly, the ghosts ignoring the inhabitants as they move through the walls from one place to another.
Once realized, matter is old news for neutrinos.
I anthropomorphize the Universe, believing it has a sense of humor. But I think sometimes the universe provides proof that I’m right.