How does a star collapse? | Cosmic Void

This section is devoted to astrophysics, so, obviously, we are talking about the destruction of those celestial objects, including the Sun, that provide us with the energy necessary for life. But, curiously, the answer to the question we are asking today is not much different from what we might say about the (self)destruction of movie stars (or anyone else), about which we hear more stories than about stars. Stars are destroyed by the use and even abuse of substances that cause irreparable imbalance. They are also ruined by bad, even dark company. Choose the movie or music stars you want to think about these forms of destruction, I will give you cosmic examples.

It is often said, a professor at the Complutense University of Madrid taught me, that the stars are a battlefield between two great enemies: pressure and gravity. Everyone is looking for their allies. And they often add that in the end there is always a winner.

I know comparisons are always odious, but they partly help to understand the problems. Imagine a hot air balloon. The walls of the latex balloon prevent air penetration. You have to blow hard so that the pressure of the supplied air overcomes the resistance of the deformation ball and inflates. If we leave the balloon loose and uncovered, the air pressure inside will try to equal the pressure outside and will not resist the pressure of the latex, causing it to deflate.

Let’s see how we compare a hot air balloon to a star. The analogue of latex walls compressing a balloon is gravity, which leads to the concentration of matter. As volume decreases, density increases. In a star, this material is a gas, mostly hydrogen. When a gas is compressed, its temperature and pressure increase. Just like the air we introduce into a balloon, the star’s gas tends to expand the star with its pressure. Here we have two competitors: gravity tends to force everything to fall towards the center of the star, pressure tends to disperse the gas. And in this great battle the star spends its entire life, including the stage before its birth as such and the process of its death or destruction. It all depends on whether the pressure can counteract gravity.

Before a star is born, and now we will say what this means, gravity will win. It is stronger than gas pressure, including because the gas clouds that give rise to stars begin their evolution at temperatures of the order of -250 degrees (compare with a temperature of 6000 degrees on the surface of the Sun). But the clouds are compressing and heating up. Temperature and pressure increase and this can counteract gravity. However, gravity is looking for an ally: light! The hot gas emits light, and this energy carried away by radiation cools the gas and the collapse continues.

Eventually there may come a time when the pressure finds its ally. Depending on the size of the parent cloud, the temperature at the center during collapse can reach temperatures so high that it causes hydrogen atoms to collide with each other. Knowing that temperature is a physical property that tells us how fast gas particles are moving, it will be clear that atoms eventually overcome their electrical repulsion and fuse to form the nuclei of heavier elements. A star was born, in the core of which nuclear fusion occurs.

Helium is formed first, although not directly; yes, synthesis occurs in parts, but that’s another story. Nuclear fusion produces energy, and with this extra energy the star’s gas receives, the pressure of the gas finally balances gravity and the star becomes stable. Gravity plus light ends up in the tables against pressure and fusion. But not forever, rivals get tired. In any case, the Sun has been in this equilibrium for 4.5 billion years, and it has yet to reach the point we wanted to comment on in this article: its destruction.

As we said at the beginning, the destruction of a star comes from the use of substances. When the hydrogen at the star’s center runs out, when one of the allies fails, gravity takes over again and the star destabilizes. This will eventually lead to its destruction, but not before stages have passed where the other elements have merged. But there will come a time when there will be no material to create the amount of energy needed to stop the collapse. And since it is impossible to stop the collapse, much more dramatic events occur. But we won’t talk about this today, because we want to talk more about ways to destroy stars.

Uncontrolled consumption of substances and their abuse is another way of destroying stars, somewhat different from the previous one. In very, very massive stars, tens or even a hundred times more massive than the Sun, the amount of matter is so large, and the collapse under the influence of gravity occurs with such intensity that their cores reach very high temperatures and thermonuclear fusion occurs. are produced much faster than on the Sun. These stars live quickly and leave behind a beautiful corpse.

Excessive consumption of hydrogen entails two things. The enormous energy they produce raises their surface temperature to a level where the mere light they emit exerts its own pressure. In other words, light exerts pressure on matter, just as a gas would! This pressure is called radiation pressure, and in massive stars it is so great that it pushes away the outer layers and destroys most of the star, which gradually dissolves. This is the case with the so-called Wolf-Rayet stars, the images of which are impressive. An example is the so-called γ Velorum (Gamma Velorum, the third brightest star in the constellation Vela), which is actually 4 satellites, one of them Wolf-Rayet, which has already lost 75% of its mass in just 5 million years. years. Their fate is even more brutal destruction as substance abuse leads to their complete collapse, resulting in a supernova. But I don’t want to go into this topic because I miss a form of destruction: bad company.

There are stars who live with the wrong people. And the companies that seem the most dangerous are not always able to destroy their partners. Let’s give two examples.

A little over a year ago, an object was discovered that sharply changed its brightness. Subsequent observations in X-rays, radio waves and the optical spectrum revealed what appeared to be a black hole that had swallowed the star. He first began by deforming it, and then tore it apart to finally eject some of the cosmic feast in the form of powerful jets of matter, accelerated to almost the speed of light. A spectacular death for communicating with the wrong person.

The last example is less expected: a normal star for being too kind. Stars can also be destroyed by donating some of their material to a companion, a white dwarf or neutron star, in such a way that it becomes so destabilized that it explodes as a supernova, taking its generous partner with it. Among these supernovae, different from those we talked about above, they are extremely interesting and useful, but that is another story.

We finish today. They seem imperturbable and omnipotent, especially our beloved Sun. But stars are born, live more or less peacefully and die, often in very cruel ways. The key is how and if they can achieve balance in their lives. But in the end everything falls, gravity always wins, it is weak, but very tenacious and destroys stars, and in a more or less cruel way.

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