PHY: Stars Part 1 - How Stars are born
Hello everyone, David here! Sorry for the long time taken to post, I've been working on the first MEEP workshop or, as I like calling it, MEEPShop! I will be the presenter and it will probably be about Astronomy, I was thinking constellations would be cool, but more on that later.
Today we will start the mini-series all about Stars! This will be divided into 3 sections: How stars are born, The death of stars and Some other facts about stars, the last one of which I will explain some other topics related to stars that will not fall on either of the three previous posts, such as Spectroscopy, Doppler's Law's relationship to systems, etc.
Let's get started then, shall we? Today's post should be a little smaller than usual, as this topic isn't very dense (see what I did there?). Regardless, for what it's worth, let's get learnin'!
WHERE DO THESE THINGS EVEN COME FROM?
From space.
Just kidding. The answer is a little bit more intriguing. It is a valid question to ask where did stars come from, and it turns out that being able to answer this allows us to unveil a lot more about a Star.
As we all know - and although this is still a little bit controversial - everything began with a big bang, a bang so big we call it the... Big Bang? Pretty lame, I know, at least it's very descriptive! The Big Bang was, quite literally, a Big Bang that created all matter that exists today. We all kind of have this image of an explosion in our heads, but immediately after that, what was this now-called-universe thing all about?
Well, a bunch of particles. Literally. Quarks, to be more specific, which eventually got together forming Protons and Neutrons which, thereafter, also got together and formed Hydrogen and Helium. So, in conclusion, space was pretty much a lot of gas for a long time. And it's from this gas that Stars are formed.
THE FORMATION OF STARS
You might recall from my last post that our Sun is made mostly out of Hydrogen, and that is no coincidence with the last paragraph. In fact, most of the Universe is made of this atom, as it is the most abundant in the cosmos, believed to account for 90% of the visible universe. The reason for that is simple. Simplicity. Yes, simply simplicity. Quite simple, huh?
You see, a Hydrogen atom is made of a Proton and an Electron, getting the crown for the simplest element in the Universe. You don't even need a Neutron, which was quite a bargain for the whole Big Bang thing (/s). Due to its extremely plain nature, it is everywhere.
These novel gases, however, in the newly formed, extremely hot universe, started fighting a "silent tug-of-war" - as is said in this awesome video by NatGeo - with a force that, as we will see, is responsible for most of what is: gravity. The gases wanted to expand, distribute themselves equally around the cosmos, but they had mass, which prompts gravity to kick in, pulling them together. This all happens in a Hydrogen dust nebula called a "Stellar Nursery".
Slowly but surely, Gravity starts winning over, tucking them closer and closer together around a center. Eventually, this force starts getting more and more intense, and the areas closer to this center start getting denser and denser, as pressure rises to extreme levels. At last, at the center, these clouds of Hydrogen subdue to such enormous pressure levels and Hydrogen atoms start being clumped together, forming Helium and releasing crazy amounts of energy. The universe witnesses, for the first time, Thermonuclear reactions.
You are not wrong if you associated this with the Sun's source of energy, as we discussed in my last post; as a matter of fact, this is most stars function, and it should not come as a surprise, for their formations are remarkably similar, unlike their deaths, but we'll talk about that later.
The crunching force of gravity keeps acting on the gas as long as it isn't fought back, which begins to happen as soon as Thermonuclear reactions start releasing energy, offering resistance to gravity while increasing its core and forming a protoplanetary disk, which is essentially dust gathering around a star that can possibly form planets in the future. At last, gravity reaches a state of equilibrium with the Thermonuclear reactions on the core, and a star is born. Voilà. L'étoile.
This is how a star is born. A really important factor, especially later on, as we discuss the death of stars, is its mass and classification. This factor is dependant mainly on how much gas was concentrated when the star was formed - the more gas, the more massive a star will be - as well as some other factors such as luminosity, surface temperature, and radius. We can classify a star based on all (or some) of these factors and it turns out that there's a very interesting diagram that represents them, the HR Diagram, or Hertzsprung-Russell Diagram.
HERTZSPRUNG-RUSSELL DIAGRAM
The HR Diagram is really complicated and we will dive more deeply into it on our next post, but let's just take a quick look into it, shall we?
This is an HR Diagram. Looks complicated, and we don't need to get really in-depth here, but let's just get a good glimpse of the overall diagram.
As you can see, the y-axis is the absolute magnitude. Notice that it decreases as we go up, which is counter-intuitive, but not really. You see, the lesser the magnitude, the brighter the star, so the way it is organized makes sense. We can't say the same for temperature, as the hotter the star, the further away it will be from the origin. The spectral class is how we classify a star given its color or temperature. Because of a little law called Wien's Law, temperature and color are related to a constant. To be more precise, λmax*T = b, in which 'b' is a constant and λmax is the maximum emitted wavelength (which determines its color). In other words, if you know the temperature, you know the color and vice-versa.
There is a nice little way of memorizing the spectral classes OBAFGKM. Just think of the phrase Oh Be A Fine Girl(or Guy) Kiss Me. Neat, huh?
For now, all you need to know besides this basic overview of the Diagram is that the Main Sequence englobes 95% of the stars, including our Sun, and such are called the "Average Stars". White Dwarfs and Supergiants or Giants will be discussed later on. There is also another type of star called a Brown Dwarf, which is essentially a very low mass star - hence the name Dwarf - formed by small amounts of Hydrogen clouds.
Well, folks, that's it for this first post! On the next one, we'll dive deeper into the death and "post-mortem" life of stars, which is highly dependant on the type of star we're talking about.
Hope you guys enjoyed and stay tuned for updates on MEEPShop. See you again later! Stay safe! Peace!
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