Galaxy – CURIOSITY

Sometimes we forget how small our knowledge of space actually is and how much more there is to discover. We know that the earth is more than 100 times smaller than the sun and that they are both part of our solar system. The solar system contains our star, the sun, and everything that orbits it. It has a huge diameter of 287.46 billion kilometers. However, our solar system is just a really small part of the galaxy, which we are part of. Scientists discovered that our galaxy contains more than 3,200 stars like the sun, and therefore perhaps 3,200 more solar systems like ours. This gives you a vague idea of how big our galaxy is. Nevertheless, we did not even talk about the fact that there are between 100 and 300 billion galaxies in the observable universe. I will tell you a little more about the unknowns of those Galaxies.

A galaxy is a massive collection of interstellar gas, dust, dark matter, billions of stars, and their solar systems that are all bound together by gravity. The majority of galaxies range in size from 3,000 to 300,000 light-years, and they are separated by millions of light-years. One light year makes up to 9.4605284 × 10^15 meters. Because of these large distances, it is very difficult to determine how many galaxies there are. However, scientists estimate that there are about 100 to 300 billion galaxies in the universe.

In those hundreds of billions of galaxies, there is no single galaxy that is identical to another. The universe, which contains all the matter in and outside the galaxies, is a maze of those many different galaxies, some of which are more similar than others. Edwin Hubble came up with the idea in 1936 to classify galaxies by grouping them based on their shape. This resulted in four categories:

Spiral galaxies

A spiral galaxy has the shape of a spinning disc with spiral ‘arms’ that come out from the central bulge. The spiral shape might be caused by the speed of the spinning motion. This speed can go up to hundreds of kilometres per second. Spiral galaxies tend to be young and active galaxies, containing active regions of star formation. Out of all the observed galaxies, more than two-thirds are spiral galaxies.

Elliptical galaxies

Elliptical galaxies are generally round but can stretch out and take on an egg shape. The universe’s largest known galaxies are elliptical galaxies, also known as giant elliptical galaxies. They can contain up to a trillion stars and can have the size of two million light-years. However, not all the elliptical galaxies are big. Some of them are also smaller and named dwarf elliptical galaxies. Elliptical galaxies are less organized and not quite as active as spiral galaxies.

Lenticular galaxie

The mix between spiral and elliptical galaxies is called lenticular galaxies. It has the shape of a lens, hence the name ‘lenticular’ galaxy. The thin and rotating shape is similar to the shape of spiral galaxies,but without the spiral arms. The similarities between elliptical galaxies and lenticular galaxies are that they both contain a little dust and interstellar matter, and both kinds of galaxies are often form in densely populated areas of space.

Irregular galaxies

All the other galaxies that don’t belong to spiral, lenticular or elliptical galaxies are called irregular galaxies. Irregular galaxies have an indistinct shape that is often caused by the gravitational influence of other galaxies nearby. They contain a lot of gas and dust, which makes them pleasant for star formation. However, in addition to their large size of irregular galaxies, they are also made up of mostly ancient stars that are dying out.

Our planet, the Earth, belongs to a solar system that is part of a galaxy, named ‘The Milky Way’. The word ‘galaxy’ is derived from the Greek word ‘galaxias’ (γαλαξίας), means ‘milky’, hence the name Milky Way. Our galaxy is a spiral galaxy, and our solar system, including the earth, the sun, and other planets, is located in one of the spiral arms of the galaxy. The diameter of our galaxy is 105,700 light-years. Scientists have recently learned that the center of our galaxy is a supermassive black hole.

Even though all the galaxies are unique, most of the large galaxies have this supermassive black hole in common. The supermassive black holes are located in the galactic centres of the galaxies. A black hole is a region of spacetime where nothing can escape from because of its strong gravity. Not even light or electromagnetic waves have enough energy for this. A supermassive black hole is the largest and strongest type of black holes. It has the same mass as hundreds of thousands, or millions to billions times the mass of the sun. A black hole is born when a giant star runs out of energy and therefore dies. The giant star implodes because its gravity becomes so strong that its centre collapses under its own weight. This explosion is called a supernova and is the birth of a black hole.

Now that you know more about galaxies and their aspects, I can imagine that it sounds impossible to travel from one galaxy to another. The hypothetical crewed or uncrewed travelling between galaxies is called intergalactic travelling. The distances are obviously huge, and travelling across those distances will take a lot of time. The fastest speed that humanity has achieved with a spacecraft is 240,000 km/h. Despite this large speed, it will still take about 19,000 years to reach our nearest neighbour outside our solar system, which is only 4,2 light-years away from us. We talk about thousands to millions of light-years between different galaxies. The technology needed for intergalactic travelling is far beyond humanity’s present capabilities, and we can therefore only talk about hypothetical intergalactic travelling. However, if you look at intergalactic travel from a theoretical standpoint, you can not say that it is impossible.

One of the options for intergalactic travelling could be the usage of a Generation ship. This would mean that we would send a spaceship with approximately a crew of 100 people into space until we arrive at our nearest neighbour outside of our solar system. Nevertheless, if we would speculate that the speed of 240,000 km/h is the fastest speed that we are ever going to reach using a crewed spaceship, it would take 19,000 years to reach that neighbour. That would mean that more than 600 generations would have to live their lives without ever leaving the small space of the ship. We would come across another problem, after this generation ship would arrive 19,000 years later. They will not only discover that humans are already there, but that they have been there for thousands of years. After the generation ship left with the thought of using the fastest speed possible, there was a new generation ship with new technologies and a higher speed that left a thousand years later. The new generation ship was therefore able to pass the older ship and arrive thousands of years earlier. That would mean the first generation ship travelled 19,000 years for nothing. This problem is also known as the Wait Calculation and contains the question “When is the optimal time for humanity to send colonists out to another star?”.

Now that you know a little more about the unknowns of galaxies, you can imagine how much more there is to discover, if we ever will. The distances are really big and so are our questions. Nobody knows if we will ever find the answers to those questions, and you will probably never know them. For now, you can enjoy the unknown of galaxies while you look up to the sky and wonder if we even want to know those answers.

20-03-2023

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