The Milky Way Galaxy
Milky Way Galaxy--Jason Ware

The Milky Way Galaxy is the home of Solar System. It was discovered by Galileo Galilei in 1610. The galaxy itself is approximately 13.6 billion years old. It is considered to be a spiral galaxy meaning that its shape and movement is consistent with the shape of a spiral. It began as a gas cloud and then over billions of years it has gained the shape of the galaxy that we now call our home in the Universe. The Milky Way is thought to consist of over 400 billion different stars. The most commonly referred to star is our Sun, which is the center of our Solar System. It is thought that there could be billions of planets in the Milky Way Galaxy, which makes our Solar System with its meager 8 planets seem like nothing.

Formation of the Milky Way

The Milky Way Galaxy is believed to have formed directly following the Big Bang. It is thought to have formed when several different galaxies all collided. It is a spiral galaxy that has several arms that shoot off in different directions. These arms consist of dust, gas, and millions upon
COBE Image of Milky Way
millions of stars. These arms stretch out from the center of the galaxy which is a spherically shaped flattened disk. It belongs to the Local Group. The Local Group is a group of galaxies that are all relatively close together with respect to the size of the Universe. It consists of 30 different galaxies, all of which are smaller than the Milky Way itself. The reason that the Milky Way has it's disk like structure is through the process of Angular Momentum. Angular Momentum is mass x velocity x distance and it tells us the measure of the amount of spin or orbital motion the Milky Way Galaxy has. The majority of the Milky Way Galaxy, since the time it was formed consists of something that has recently been discovered and researched more in depth. Dark Matter and Dark Energy are the most abundant things that are found in the Milky Way Galaxy and they have been there since its formation.

What is Dark Matter and Dark Energy?

Composition of the Cosmos--LSST

Dark Energy makes up about 70% of the Universe and Dark Matter makes up about 25% of the Universe. There is still more that is unknown about Dark Matter and Dark Energy than there is known, but since there is so much of it in the Universe scientists are racing to find out more information on what exactly it is. NASA has come to the very basic conclusion that dark energy is a property of space.
Dark Energy is basically empty space. The only way to figure out what exactly this Dark Energy is is to continue researching and find more data.
We know way more about what Dark Matter is NOT than what it actually is. According to NASA we know that Dark Matter is Not:
  1. It is dark, mean
    Addison-Wesley Longman--Dark Matter
    ing that it is not in the form of stars and planets that we see
  2. Dark matter is not antimatter, because we do not see the unique gamma rays that are produced when antimatter annihilates with matter.
  3. It is not in the form of dark clouds of normal matter, matter made up of particles called baryons
  4. We can rule out large galaxy-sized black holes on the basis of how many gravitational lenses we see.

Main Components

1. The halo is a roughly spherical distribution which contains the oldest stars in the Galaxy,
2. The nuclear bulge and Galactic Center.
3. The disk, which contains the majority of the stars, including the sun, and virtually all of the gas and dust

Size of Milky Way--Addison Wesley

The Halo- It is the collection of the oldest stars in the galaxy that range from being 10 billion years old to about 15 billion years old. The Halo is also thought to be filled with hot and highly-ionized gases.

The Disk- It is the flattened portion of the galaxy that rotates and contains the Sun and other stars that are considered to be intermediate or young. It is unbelievable to think that the sun only rotates around the center of the disk every 250 million years.

The Galactic Center- There is little known about the center of the Milky Way, but in recent years researchers have begun to think that the Galactic Center is a huge black hole. This black hole would be the reason that the Milky Way orbits and maintains its shape in the way that it does due to the strong gravitational pull that the black hole is thought to have.

The Bulge- The bulge consists of much older stars and are called the globular star clusters.

The Spiral Arms- These arms consist of interstellar matter, diffuse nebulae, and young stars. There are thought to be 6 different arms that stretch out from the center of the galaxy.
  1. The Outer Arm, Obscured Arm
  2. Perseus Arm
  3. Local Arm, Orion Arm (Where our Solar System in located in relation the galaxy)
  4. Sagittarius Arm, Sagittarius-Carina Arm
  5. Scutum-Crux Arm
  6. Norma Arm

Milky Way Galaxy Arms

Size of the Milky Way

Size of Milky Way

Diameter: 100,000 - 120,000 light years across
Mass: 1 - 2 Trillion times the Mass of the Sun

So What is the Black Hole in the center of the Milky Way?

The Black Hole at the center of the Milky Way is referred to as Sagittarius A and it is considered to be supermassive. A stellar black hole is formed when old stars collapse and there are many of these within our solar system and cause little to no problems. The density within the supermassive black hole at the center of the Milky Way Galaxy has
Black Hole

such a huge mass that not even light is able to escape from its gravitational pull, hence the name Black Hole. There are hundreds of stars that are orbiting around the black hole, but they are orbiting at an intensely greater speed than stars would typically be orbiting. It is estimated that some of the stars closest to the black hole are orbiting at a rate of 300 million miles per hour. This speed is ten times the speed that most stars orbit in the Milky Way Galaxy whether they are disk stars or halo stars. The reason that they are orbiting so quickly around the galactic center is because the gravitational pull from the black hole is making them accelerate. Eventually these stars will be sucked into the black hole by the gravitational pull and will never be heard from again.

Interesting Facts

  • The Milky Way Galaxy continuously "eats" up other Galaxies making it larger on a regular basis. Currently it is in the process of eating the Canis Major Dwarf Galaxy
  • Neighboring Andromeda Galaxy is approaching our galaxy at speed somewhere around 100 to 140 kilometers per second, which means that The Milky Way may collide with Andromeda Galaxy in 3 to 4 billion years.

Additional Resources Besides Graphics

Cain, Frasser. "Milky Way." Universe Today. N.p., 11 26 2008. Web. 2 Dec 2011. <>.

Frommert, Hartmut. "Milky Way Galaxy." Messier. N.p., n.d. Web. 2 Dec 2011. <>.

Smith, Gene. "The Structure of the Milky Way Galaxy." University of California, San Diego Center for Astrophysics and Space Sciences. N.p., n.d. Web. 2 Dec 2011. <>.

"Dark Energy, Dark Matter." NASA Science. N.p., n.d. Web. 2 Dec 2011. <>.

"Formation of the Milky Way." Galaxy Zoo. N.p., n.d. Web. 2 Dec 2011. <>.

"LSST." Dark Matter and Dark Energy. N.p., n.d. Web. 2 Dec 2011. <>.

"Milky Way Galaxy Facts." Interesting Science Facts and Articles. N.p., n.d. Web. 2 Dec 2011. <>.

"'Supermassive' Black Hole Found In The Center Of Our Galaxy." Science Daily. N.p., n.d. Web. 2 Dec 2011. <>.

"What is a Black Hole?." NASA. N.p., n.d. Web. 2 Dec 2011. <>.