We live in the Milky Way galaxy which is made up of hundreds of billions of stars. There are over 200 million galaxies in the known universe, each one is unique, enormous and gigantic. Galaxies had a violent birth and they will die a violent death. But where do galaxies come from?? How do they work?? What is their future?? And how will they die??
This is our galaxy, the Milky Way. It’s over 12 billion years old. It’s basically a huge disk with giant spiral arms and a bulge in the middle. It’s just one of the huge numbers of galaxies in the universe.
Galaxies are first and foremost a large collection of stars. They are stellar nurseries. Where stars are born and they die. The stars in a galaxy are formed in huge collections of dust and gas called nebulas.
These are the pillars of creation in the eagle nebula.
Our galaxy contains billions and billions of stars and most of them are systems of planets and moons. But for a long time we knew nothing about galaxies. About a century ago we thought the Milky Way was all there was. Scientists called this our island universe. For them no other galaxies existed. Then in 1964, an astronomer Edwin Hubble changed that thinking. Hubble was observing the universe with the most powerful telescope at that time, the 254cm Hooker on Mount Wilson near Los Angeles. Deep in the night he saw fuzzy blobs of light very far away. He realised they weren’t individual stars at all; they were whole cities of stars, far beyond the Milky Way galaxy. The astronomers had an existential shock. In one year the ideas changed from the universe being a single galaxy, the Milky Way to the universe consists of billions of galaxies. Hubble had made the biggest discovery in the field of astronomy.
This is the whirlpool galaxy, consisting of a whopping 160 million stars.
This is the m87 galaxy. It’s one of the oldest galaxies out there. The stars in this galaxy glow gold.
This is the sombrero galaxy. It has a huge glowing core, with a ring of dust and gas around it.
Galaxies are gorgeous; they represent in some sense the basic unit of the universe itself. They are like gigantic pinwheels twirling around in space. They are like fireworks created my mother nature.
But galaxies are big, very big. On earth, distance is measured in kilometres. But in space, distance is measured in light years, the distance light travels in 1 year, which is just under 9 and a half trillion kilometres. Our galaxy is about a 1, 00,000 light years across, but this is still a spec in the cosmic distance.
Our Milky Way galaxy may seem massive to us, but it is pretty small compared to some other galaxies out there.
Andromeda- our closest neighbour is over 2, 00,000 light years across, nearly twice as big as the Milky Way
M87- the largest elliptical galaxy in our own cosmic backyard is larger than Andromeda
But even m87 is tiny compared to IC1011 the largest galaxy in the known universe. It is over 6,000,000 light years across, 60 times bigger than the Milky Way.
We know that galaxies are big and they are everywhere, but where did they come from??
The universe started in a big bang, an extremely hot and dense phase which took place 14 billion years ago (please refer to the article “the moment of creation” for further details). Galaxies couldn’t form in such extreme conditions, so obviously they must have formed after the big bang.
It takes gravity to form stars, and even more gravity to form galaxies. But where did this gravity come from?? To understand this, the scientists use the Hubble telescope. The Hubble telescope is one of the most powerful telescopes; in fact it is so powerful that it helps us to peer back in time. How?? The Hubble telescope sees lots of galaxies, but the light we see today from those galaxies left them 100s of millions of years ago. It has taken all that long to reach us. So what we see today is in fact the ancient history of those galaxies. So the further we see, the more we peer back in time.
But there is a limit to how far the Hubble can see, to see even further, we need to use an even bigger telescope, a telescope too large to launch into space. But now we have such a telescope. In the dry desert of northern Chile. It’s called the A.C.T i.e. the Atacama Cosmology Telescope. This telescope unlike others uses microwaves. Hence it is not only able to see the distant galaxies but also how they grew. Using this telescope astronomers are trying to understand how stars evolve from a group to a network of stars we see today.
Early galaxies were a mess. They were simply huge clusters of stars, dust and gas. But today galaxies look neat and orderly. So how do chaotic galaxies transform into beautiful spiral and elliptical galaxies we see today. The answer is GRAVITY. Gravity controls the shape and future of galaxies. And there is an unimaginably destructive source of gravity at the heart of most galaxies. And there is one very deep at the centre of our own milky way.
We all know that galaxies are very large clusters of stars, which come in all shapes and sizes. But the question is whether all the galaxies were always the same. Obviously, the answer is NO. The very first young galaxies were ugly and chaotic, consisting of stars dust and gas. Even our own milky way was once a cluster of many baby galaxies. What pulled all this together is gravity. Gradually gravity pulled all the stars inward until they started spinning faster and faster. At some point of time they were spinning so fast that they formed a disk. The stars and gas were swept together into giant spiral arms. This process was repeated billions and billions of times across the universe, until the universe we see today was formed.
All galaxies seem to be unique, but they all have one thing in common, they all seem to orbit something. For years scientists wondered what could be powerful enough to change how a galaxy behaves. What emerged from years of research was a single term, a BLACK HOLE. But not just any black hole, a super massive black hole. The first clue that super massive black holes existed was that there was an immense amount of energy radiating from the core of most galaxies. This energy was produced by the black hole when it was feasting at the material around them. Sometimes they absorb so much, so fast that they release huge beams of pure energy from their poles, which stretch for trillions of kilometres. This event is called a quasar. But our galaxy, the Milky Way does not have a quasar shooting out of its centre. Does that mean that our galaxy doesn’t have a super massive black hole at its centre??
A team of scientists set out to find the answer. They used the Czech telescope to monitor the centre of our galaxy. They noticed that the centre of the Milky Way was very chaotic. There was a huge amount of energy radiating from its centre. And the stars which were close to the centre were whizzing around at tremendous speeds. The stars here were moving at speeds in excess of a million kilometres per hour. Only one thing could be powerful enough to fling stars like that – a super massive black hole.
This discovery changed the way scientists look at the universe. But there was a problem with this discovery, a super massive black hole may be very powerful, but it didn’t have enough gravity to keep the galaxy together. According to the laws of physics, galaxies should fly apart. So, why don’t they?? This was a mystery until a Swiss astronomer Fritzwicky started wondering why galaxies group together in clusters. After years of research he devised the theory which stated that something unknown was at work. He named it dark matter.
To prove this theory, scientists created a virtual galaxy, with virtual stars and virtual gravity. But to their surprise the virtual galaxy always came apart. The same thing happened over and over again. After many tries scientists added the extra gravity which was supposed to be produced by dark matter, and to their surprise, they got a perfect galaxy. So now we know that dark matter is basically the adhesive which holds galaxies together and prevents them from falling apart. Some scientists also say that dark matter was responsible for the creation of galaxies. But even to this very date, scientists have no idea what dark matter is.
Dark matter is so weird also because it’s made up of ghostly particles. You cannot touch it, feel it, see it, smell it, taste it or even push against it. It may pass right through you as if you didn’t exist. It’s everywhere around is and yet we have no way of detecting it. Almost 83% of the universe consists of dark matter. And all the stars, planets, moons etc. are made up of the remaining 17%. Dark matter is very important of the universe. Without it we wouldn’t exist. And recently it’s been detected in space. It’s clear to us now that dark matter is a crucial part of the universe. It was responsible for the birth of many galaxies and it prevents them from falling apart. But still we know so little about them.
Using massive telescopes, scientists have been able to spot billions of galaxies. But when we look at the night sky, galaxies seem isolated. But actually they live together in groups called clusters and these clusters of galaxies are linked together in super clusters containing tens of 1000s of galaxies. So where does our milky way galaxy fit it??
If we take a look at the big picture, our galaxy is a part of a local group of galaxies consisting of 30 or more galaxies. Our galaxy and the Andromeda are the biggest galaxies in this local group. If you look at the even bigger picture, the Milky Way is a part of the Virgo super cluster of galaxies, which contains over a million galaxies. But it doesn’t end there; these super clusters are connected into structures called filaments.
A project called the Sloan digital sky survey has been started by a group of young and ambitious scientists. The goal of this project is to create a 3-D map of the entire universe. Scientists working in this project have discovered a filament which is 4.1 billion light years across!!!!! It’s called the Sloan great wall and it’s the largest known structure or pseudo-structure in the universe discovered so far.
But scientists have taken this idea even further; they have made a virtual universe in a super computer. Here you can’t see individual galaxies nor galaxy clusters, what you can see are super clusters linked together in filaments. When we look at the entire universe, we can notice a filamentary pattern, a cosmic web containing galaxies and clusters of galaxies that light up the universe. On the largest of scales, the universe looks like a giant sponge. Each filament home to millions of super clusters, held together by dark matter. This dark matter holds together this mega structure of the universe. This is the big picture, this is where we fit in, and this is our universe….