Looking into the stars

Hello! It has been a long time since I last wrote an entry to this blog... Life has been difficult to manage, many responsibilities came and go, and so did my interests.

Today's entry will be about my newest interest: astrophysics.

Introduction

Solar system

So I started getting interested in astrophysics once I accidentally learned a couple of facts about the universe which completely changed how I see it forever. Let's talk about those facts.

So the first thing that completely blew my mind was the distance and size. When we think about space we think about something that's very hard to reach, something bizarre, infinite... But very little people realize the true vastness of it, so let's build a tower of concepts together.

Let's start with stars. Now we all know one big star close to us which is the Sun. I don't think people truly realize it's a star unless they start thinking about it, most people just brush it off as the sun and don't give it much thought after. Now, let's ask ourselves two simple questions: 1) How big is the Sun?; 2) How far away is the Sun.

The sun

To answer our first question, it is massive and I mean massive, it's radius spanning over 696,000 kilometers, is around 285 times that of our planet's. It's a massive nuclear reactor which creates incredible amounts of heat and energy which in term heats us and gives us our days.

To answer our second question, we get into our first basic unit of astrophysics. Now, distances in space, even in our solar system, are tens or hundreds of millions of kilometers, so using kilometers becomes very inconvenient at this scale. That's why we came up with a more suitable unit of distance called an astronomical unit. It is abbreviated as AU and is exactly the distance between the Earth and the Sun, which is 149,597,900 kilometers.

Astronomical unit

Stars and light

With these two questions out of the way, we can start seeing just how massive things are getting in terms of size and distance, and that's only our solar system. With the AU out of the way, let's now talk about light.

Many of you don't think much about light, it's there illuminating whatever surroundings it hits. For us astrophysicists and physicists in general, light is incredibly complex and is of incredible importance, especially for distances. Complexity of light is beyond this blog's field of complexity so I will not get into wave-particle duality and many other complex things about it, however, what I will talk about is the speed of light.

Now, how did we get here, from distance to speed? Well, space is so vast that it takes light a lot of time to travel from one place to another. Some of you may or may not know this, but the speed of light is the universe's speed limit. We cannot go beyond it nor can we reach it unless we don't have mass. Let that sink in, it takes the fastest thing in the universe a lot of time to traverse from one place in space to another, that's how vast it is. With that out of the way, let's talk about why we need to know the speed of light and what role does it play in astrophysics.

Distance. Many of you heard of the term β€œlightyear”. A lightyear is the distance that light travels in a year. We will be using this A LOT wherever we go in astrophysics, so keep it in mind. A lightyear is 63,241 AU, 63 thousand distances from Earth to Sun.

Our closest stars to us are very very far. It's a very scary thought, but it's incredibly bizarre. Closest to us star is called Proxima Centauri, only 4.2 lightyears away. 4.2 might seem like a very small number, but it is in fact 265,612 AU. If we imagine a line from east to west coast of United States as that distance, then we would be a grain of sand on the east coast and Proxima would be a grain of sand on the west coast.

Proxima Centauri

A bizarre consequence of the distances in space is that no matter where you look you will always see the past. As it takes light a lot of time to reach you, the light you will see coming from stars is the light that left that star as many years back as it is lightyears away from you. Light we see from Proxima Centauri is 4.2 years old, we see it as it looked 4 years ago. Betelgeuse, one of the most well known stars, we see the way it looked around 500-600 years ago.

Betelgeuse in Orion

More on stars

Many don't know how stars are born. Where did they come from? How did they form? Well we have our answers. I will extremely oversimplify this part for brevity and ease of understanding.

Stars are born from nebulae. Nebulae are incredibly big and vast clouds of gas and matter, where our stars are born.

Eagle nebula

There are multiple types of nebulae, and all of them act differently. Now how do stars form? Well as matter clumps together, it slowly collects more and more, which creates a protostar. As the star gets more and more matter it becomes a ball with a disk of matter around it. As the ball becomes bigger the density of it increases, which creates a core where under immense pressures commences nuclear fusion, creating plasma and heat. Planets form in a similar way minus the fusion inside of those disks around the protostars.

From stars to galaxies

Every star has it's lifetime, as it lives on it becomes bigger and bigger but it's core loses more and more of the fuel needed to keep the fusion going. As a star depletes it's core of fuel it becomes so dense that it collapses, which creates two different outcomes: 1) It goes supernova 2) It becomes a black hole

Now which one it is depends mostly on it's mass. If it's of immense mass, it will become a black hole or a neutron star (A very very tiny star with a VERY big mass, size smaller than a planet, mass hundredfold of the sun).

A black hole

If it's of a lesser mass, it will most likely go supernova, a massive explosion which erupts gasses and matter and creates a nebula, which we covered earlier.

Supernova

Knowing this is important for understanding galaxies, and you will find out why shortly. But before that I will explain what galaxies are. Galaxies are an INCREDIBLY BIG amount of stars and matter which all orbit around a centre as a sort of a disk or a spiral, our own galaxy is not an exception. It is incredibly big, spanning over 170,000-200,000 light-years.

Each galaxy has a centre, and in that centre must be immense mass for the galaxy to orbit around. Milky way orbits around a supermassive black hole called Saggitarius A*. It is so massive that the entirety of our galaxy orbits around it. It's mass is millions that of our Sun. Black holes might sound scary, and truly, they are, but do not fret that we have a super massive one in the centre of our own galaxy, contrary to popular belief, black holes don't simply eat everything that exists around them, they consume anything that gets too close.

Vastness

There is too much for me to cover in a single blogpost, so I will be ending this post here. I will end it with a word about vastness once again. Now that we've learned what galaxies are and how big they are, try to imagine our own galaxy. It has trillions of billions of stars in it, much like our sun. It is so unimaginably big that it's very hard to put our heads around it, but even then, our galaxy is like a little star among the trillions of billions of other galaxies in the observable universe, forming groups of galaxies that become like constellations of stars here to us on Earth, to whoever observes the galaxies if they zoom out far enough.

Milky way with galaxies behind it

Thank you for reading and I hope I can share my knowledge with you. Await more as I haven't covered enough.