Galaxies are unimaginably massive crucibles of creation and destruction; places of tranquility and calm and storm and explosion! They are vast structures made up of stars, gases, stellar dust and many other objects. Many galaxies have within their centers super-massive black holes. Within a galaxy the life and death of stars are played out. They hold both dying stars and stellar nurseries.
Galaxies are assembled into super structures. Not only are stars gathered together to form galaxies but then they, in turn, form small groups of galaxies. The group that the Milky way resides in is called the Local Group. Then these smaller groups are organized into larger clusters and these in turn form super clusters of galaxies. When you stop to examine this phenomenon, you find that the universe is not some random, disorganized mess but is made up of highly structured, organized walls of galaxies. Some scientists have mentioned that they look as if they are spaced out into honey-combed structures expanding towards an unknown and unseen force that some scientists have called the Great Attractor.
So what of our little Milky Way galaxy? Of galaxies, it is rather small but it is still a beautiful and fascinating structure. Let us examine our own, shall we? The Milky Way is 100,000 million light years across in diameter and is about 13 billion years old. It is still under progress and construction. It is made up of old and new stars; it’s like a factory where the old ones die out and become material for new stars to come into being. The name Milky Way derives from the Greek word “galact” the Greek word for milk. At night it’s arm looks like a shining river of stars! The Egyptians looked up at the night sky and saw this beautiful sight and imagined that it was the pathway to the after life. But during the time of the ancients, parts of the arm were all humans could see. It was impossible for them to know what the Milky Way actually looked like. Today we have a far better, more accurate picture of what our galaxy looks like.
Our solar system is in the outer, calmer area of the galaxy, the far reaches or “the sticks”. The galaxy hub or the middle are where most of the older stars reside. Most of these older stars in the hub if the galaxy are massive red giants, far bigger than our sun. The hub of any galaxy is too dangerous and full of radiation for life to survive there. Globular clusters make up the size and content of most galaxies. Globular clusters are groups of stars that are as old as the universe itself. Most stars either come in these globular clusters or in pairs. Our sun is rare in that it is a loner.
Galaxies are classified into four shapes:
Elliptical – made up of old stars and doesn’t spin or revolve. Elliptical galaxies tend to be very large and uncommon.
Lenticular – Has a bulge and a disk. No new star formation.
Irregular – Possess no regular shape. They tend to look like the Magellan clouds in space. Their irregular shape comes from collisions with other galaxies. Some Magellanic clouds are also seen as dwarf galaxies.
Spiral – tend to be smaller. They move and rotate and carry both old and new stars. Tend to be more common. The Milky Way is a spiral galaxy.
One of the mysterious things about the Milky Way is the bar near the center which is made up of 30 million stars. It is the disc and bulge at the center. In the middle of this is a super massive black hole. Among super massive black holes, this one isn’t impressive but rather small, but it is more massive than anything else in our galaxy. The arms are just as spectacular as the center! In the spiral arms construction of new stars is always happening. These arms are also made up of a lot of dust and the giant stellar dust clouds block much of the light emanating from our luminous Milky Way. This may actually serve as a protection for us and all life on earth the same way that the placement of our solar system near the edges of one of the spiral arms instead of near the center is also a protection.
Our solar system takes 250 million years to go around the galaxy so it has been around 18 times since the beginning of the universe. In the past, much of what resides in the Milky Way was closed to us – we couldn’t see it until radio and x-ray astronomy made it possible. Today, by using these new techniques in astronomy and photography astronomers can truly see what the Milky Way looks like, determine how old it might be and examine its structure. It used to be that the center of our galaxy was a mystery to us. Today, scientists can now see and study the activity surrounding the super-massive black hole at the center.
Another thing we can now study in more detail are the spiral arms. There are four major spirals that make up the arms of the Milky Way: the Perseus Arm, Sagittarius Arm, Centaurus Arm and Cygnus Arm. Our Solar System is in a minor arm called the Orion Spur. The spiral arms are called density waves. Stars and other objects can move in and out of these waves. Density waves are compression waves. As the stars and other objects move through the galaxy through these waves the stars bob up and down and in and out of the spiral arms.
The massive interstellar cloud and gas-like nebulae are the nurseries of the universe within the galaxies and make up much of what we see in the universe. Many of these nursery, cloud-like formations are in our own galaxy and there is one more wonderful mystery that we see taking place in our Milky Way – it is called the Paradox of Youth by some scientists: near the super-massive black hole and the ancient, massive red stars that revolve around it, also exists a star nursery. Stars are dying and being born right near the same space!
