Astronomy_mnr

From Big Bang to Galaxies

15 billion years ago our Universe exploded out of nothing, but in a very short time span many important elements of today were made. This unexplainable explosion is now called "The Big Bang". The explosion began with the Universe being packed into a space smaller than an atomic nucleus, but within a flash it changed into about the size it is today. The Universe was a dense mixture of radiant energy and exotic particles, such as quarks. While the radiant energy was made into matter and then turned back into energy, the quarks were forming into protons and neutrons. The temperature of the Universe was dropping rapidly, but even so, most particles were being annihilated because of the intense heat. After a mere three minutes, a quarter of the protons and neutrons combined to form helium nuclei, but after this, very little happened for 300,000 years. When the temperature made its way down to 3000 degrees Kelvin, the particles were finally able to become atoms without being torn apart due to the heat.



The Formation of Galaxies

Two billion years post The Big Bang, the formation of galaxies began. Galaxies started to form because of gravity causing clumps of atoms to grow and get denser. These clumps became galaxies similar to ours, the Milky Way. Our galaxy formed when the Universe was three billion years old. It started as a huge sphere of gas; some gas became stars while the rest of the gas settled into a disk around the central bulb, making spiral arms. The Milky Way Galaxy is a spiral galaxy, but there are also elliptical and irregular galaxies. At the beginning of the formation of galaxies, there was much more colliding of galaxies to form larger galaxies than there is today, but even so, our galaxy is hypothesized to collide with the Andromeda Galaxy someday.



The Structure of the Galaxy

The Milky Way Galaxy is a huge cluster of stars, gas and dust; it is the galaxy that we are part of. If one is viewing the Milky Way on a side view from 500,000 light years away, one would see a flat disk of stars 100,000 light years across and 1.5 light years thick. There is a thin layer of gas and dust in the middle of the disk, and in the center there is a huge bulge about 20,000 light years across. Our sun and solar system are about halfway out from the central bulge of the galaxy. Other stars surround the Milky Way like a halo. If looking down on the galaxy, one would see four spiral arms winding out from the bulge. In the arms, there would be blue stars and pink hydrogen gas. The central bulge would mostly consist of red and orange stars. In the central 15 light years of the bulge, there is most likely a massive black hole surrounded by gas clouds and dust. These are the different parts of the Milky Way Galaxy.



The Rotation of the Galaxy

The Milky Way Galaxy turns as a whole, but each part also turns individually. Each star and cloud is in its own orbit, yet they all orbit together as well. It takes our sun 250 million years traveling at 250 kilometers per second to go around once. Even though it should take the stars at the outer edge of the galaxy longer to complete their orbit, for some reason they just travel more quickly than the inner stars. This shows that there must be some dark matter pushing on the stars, causing them to travel faster. No one knows what this matter is, but hopefully we will someday find out what is causing some stars in our galaxy to revolve more quickly than they are supposed to.



The Formation of the Planets

Planets started forming around four and a half billion years ago, starting out as gas and dust but becoming much larger masses. When the sun formed and became a thin disk with a proto sun in the middle, solid material began to clump into bigger particles in the disk. These clumps were called planetesimals. The planetesimals collided; the ones that collided quickly broke into smaller pieces while the ones that collided slowly formed bigger objects. Some planetesimals slowly collided so many times that they formed into four huge masses, which we now call Jupiter, Saturn, Uranus, and Neptune. Because of the many collisions in the inner solar system, smaller planets such as Mercury, Venus, Earth, and Mars were formed. Now, it is less common for planets to form than it was four billion years ago.



The Formation of the Moons, Rings, and Galaxies

<span style="color: #800080; font-family: Arial,Helvetica,sans-serif; font-size: 11pt; line-height: 150%; margin: 0in 0in 0pt; text-indent: 0.5in;">Though moons, comets, and rings are all formed in different ways, they all start out as planetesimals. Planetesimals that are captured by a planet are called moons. Comets are formed when icy planetesimals from the outer solar system reach the warmth of the sun. Finally, rings are created by stray planetesimals and comets being crushed and blown apart by gravity when they get too close to a giant planet. Even though these three objects of matter are all made up of planetesimals, they have each gone through different formations that make them what they are.

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