G8 – Solar Systems, Galaxies and the Universe Approaching -04

Formation of Galaxies

At one time, it was thought that galaxies formed in a similar way to our solar system. This is known as a top-down theory of formation. The theory is quite simple yet no longer widely accepted. The theory was first proposed in 1962. It explained that galaxies formed from even larger clouds of gas and dust. Gravity acted on matter, and just like in the solar system model, caused the gas and dust to rotate. As the gases cooled, parts of the spinning dust cloud broke up in smaller clouds. These smaller clumps of gas and dust are believed to have formed the billions of stars in a galaxy. This theory of formation has come under scrutiny in recent years. It does not accurately match more recent observations.

When evidence no longer supports a current theory, scientists begin to look for a new and better explanation. They can modify the current theory to match observations. They can even abandon the theory completely and develop a new one.

One thing scientists do agree on is the major role that gravity plays. There is agreement that gravity plays a huge role in the formation of the universe and all of its components. Some astronomers think that there is a giant black hole at the center of our galaxy. If correct, it is thought this black hole is what helped create our galaxy.

Our Neighborhood

Our galaxy, the Milky Way, is a spiral galaxy. It contains roughly 400 billion stars. The disk is about 100,000 light years across. That means it takes light 100,000 years to travel this distance.

This is an artist’s sketch of the Milky Way Galaxy. The Sun and solar system (and you!) are a little more than halfway out from the center.

Our solar system is located within one of the spiral arms. Most of the stars you see in the night sky are in this spiral arm. We are a little more than halfway out from the center. Notice the arrow marking our location in the galaxy. There are billions of other galaxies in our universe. Even the closest of these galaxies are very far away. The closest to us is the Andromeda Galaxy. It is over 2.537 million light years away.