We’ve always been drawn to the cosmos – since the dawn of mankind, we’ve always looked up in wonder at the night sky. And though their positions change over time, we’ve always seen the same things: stars.
These stunningly large celestial bodies have been the topic of fascination and research for millennia; stars artwork is one of the oldest forms of art known to mankind. And it’s no wonder – there are many things to be fascinated about when it comes to these night-time giants. With that in mind, let’s go over some of the basics of stars – the most important building blocks of every galaxy.
What Are Stars?
In the simplest of terms, stars are large celestial objects whose mass mostly consists of helium and hydrogen. These two elements power the nuclear forges that produce the heat and light which is the basis of life on our planet – and possibly, throughout the universe.
Our Sun is the closest star, which is why we see it clearly in the sky. All other stars appear as specks of light because they’re thousands of light-years away.
We can’t reasonably claim to know how many stars there are in the universe, but we know that our Milky Way alone contains over 300 billion stars. And every star’s lifecycle lasts for billions of years – an amount of time we simply can’t comprehend from the perspective of a single human life.
Also, the bigger a star is, the shorter it will last – its mass will burn out quicker. And its birth begins inside dust clouds filled with hydrogen; you probably know them as nebulae. Throughout thousands of years, dense matter collapses under its own weight inside these nebulae, and protostars are born in the process.
The pressure inside a protostar starts generating higher and higher temperatures – and over time, after millions of years, the core temperature reaches the levels necessary for nuclear fusion. At that moment, a star’s core ignites – and the main part of its life begins.
All of these stars are in a constant state of stable nuclear fusion, which means they turn hydrogen into helium and send out x-rays. A stupendous amount of energy is released in the process – which is why the stars are so shiny and hot.
Different Star Categories
The way we see the stars isn’t just decided by their positioning, though it plays a role – some are simply brighter than others. And this brightness depends on the amount of energy they release and their distance from Earth. The first factor is referred to as luminosity. Also, different stars have different colors depending on their temperatures.
We see the hottest stars as either blue or white, while the cooler ones appear red or orange.
Depending on all of these factors, we classify stars into white dwarfs, main sequence stars, dwarfs, supergiants, and giants. As you may have guessed, the supergiants are the largest stars, and their radius can be thousands of times bigger than our Sun’s.
Speaking of which – how does our own start fit into all of this? Well, our Sun is a main sequence star. And right now, it’s around 4.5 billion years old. It’s also an average-sized star in the yellow dwarf category. You don’t have to worry about it going out either; most astronomers believe it has billions of years before the end of its main sequence phase.
Stars’ End
So, what happens when a star reaches the end of its lifetime? By that time, most of a star’s hydrogen has already turned into helium. And that helium drops to the star’s core and increases its temperature in the process. As a result, the outer hot gas shell expands. The entire star seems to swell, and this is known as the red giant phase.
However, depending on the size of the star, its story can have a few different endings. In most cases, the red giant stage comes before a star completely sheds most of its mass and becomes a (comparatively) tiny body – a white dwarf.
This white dwarf proceeds to cool down, but that process also lasts for billions of years. However, if the star in question was in a binary star system, it may take some excess matter discarded by its companion star; in the end, both star surfaces explode in a bright nova.
If it’s just a single star, it simply cools down over eons and stops producing energy in the end. At that point, scientists speculate that the star becomes a black dwarf; a celestial mass that produces no heat. However, it’s worth noting that this phenomenon has never been observed in practice.
However, we have observed the end of larger stars – the massive ones forgo the path of a white dwarf and choose to go out with a literal bang. You’ve probably heard of this event; we call it a supernova. This immense burst of energy leaves behind a small neutron star or, if the previous one was big enough, a massive black hole.