Now, let’s get to my “findings” of the Milky Way Galaxy. First, a definition of a galaxy: a collection of stars and interstellar material held together by gravity. Scientists discovered the name Milky Way from the band of light that is seen overhead on very dark nights. Older civilizations names it the Celestial River. Essentially the Milky Way is considered a large galaxy with 200 to 400 billion stars. Scientists, understandably, can’t agree on a more exact number. The Milky Way is interestingly shaped like a disk, although this is common among galaxies. This disk has a diameter of 100,000 light years with an average thickness of 10,000 light years, which increases to 30,000 light years at the center, or nucleus, or the spiral. Just so everyone is up-to-date, a light year is the distance light travels in a year, considerably a little bit more than a standard “earth year.”
The Milky Way has extensions which are called spiral arms. There are currently thought to be six main arms, which make the Milky Way a spiral galaxy. Bur the universe is of course, always changing. This is shown be evidence that now says our galaxy could include a bar-like area of “new” stars. This bar would make the Milky Way now a barred spiral. More evidence of our galaxy’s evolution was found in 1951 when William Morgan and his scientific team discovered that both the Orion and Preseus arms of the galaxy had their own spiral arms, too.
The Milky Way is compiled of many things, including interstellar gas, dust and stars. The biggest star is well known to be the sun. This star that we all hope for on rainy days and enjoy on the beach is on the Orion Arm of the spiral. This arm connects to both the next inner and outer arms. It is two-thirds away from the center of the Milky Way, a trip of about 28,000 light years. From pictures you would see that there is little to see beyond the sun’s orbital distance from the center of the galaxy. The curve of the galaxy makes one think there is a great deal of mass, but there is no light there. This is called the dark matter problem, and states that the halo of our galaxy is filled with a mysterious dark matter of unknown composition and type.
Our galaxy also has a circle of star clusters, called a Stellar Halo. This halo extends 130,000 light years away and surrounds the whole galaxy. The unique formation has puzzled astronomers for quite a while. A few believe that the halo was the first development. The gravity then pulled at this halo to shape the Milky Way’s center disk. While this pull was still collapsing, stars continued to evolve; causing their materials to explode and force the debris through the “winds” and soon the said explosions and debris for the last part of the disk. This theory is called the “Outside-In” theory, in layman’s terms, because the galaxy was from the outside halo and then drew itself in. The other common theory is quite the opposite. The disk formed from a cloud of unknown material, from unknown regions. The halo then formed as other clouds, also unknown, were drawn into our galaxy by its gravitational tidal. No one as of yet knows which theory is closer to the truth, or if either has hit upon it.
But, the Milky Way is not just a bunch of stars grouped into secular formations. It also contains some distant clusters, two other close galaxies named the Magellanic Clouds and four smaller galaxies. All of these “sub-galaxies” and clusters make up the mass of our galaxy, and have helped it to evolve into what we now know and love it as. Other factors defining this evolution are broken into two populations. Population one includes the arms and center plain containing interstellar gas, cosmic dust, and bright, young stars. Population two is made of the Stellar Halo, the spaces between the arms and the central core, which has the older, duller stars. What is left of the galaxy has either suddenly collapsed or is collapsing in stages into population one, which is still forming. The current ago of our galaxy is estimated to be around 13.6 billion years old, nearly as old as the universe itself.
While all of this does contribute to the mass of the Milky Way, the main attribute of our galaxy is a group of old stars in the middle. As said earlier, in the dead center of the Milky Way is a nucleus, this “brain” of the galaxy is thought to contain a million solar mass black hole. This pulls gravity and the “tidal waves” towards it and causes our galaxy to continue to amass other clusters and galaxies.
The Milky Way, as we have now found out, has never stopped evolving. It continues to grow by “eating”, so to speak, smaller satellite galaxies. As you are sitting there reading this, the galaxy is joining with moth of the Magellanic Clouds, and will be for the next 100 million years. An earlier example of this was found in 2003. A galaxy previously unknown was found colliding with the Milky Way. The galaxy and its red stars are still currently being pulled into the Milky Way. This galaxy, now known as Canis Major, will soon lose its structure, and is still 25,000 light years away from the center of our galaxy.
This is not the only one currently on a collision course for the Milky Way. The biggest and most destructive will be the Andromeda Galaxy. In a short two billion years the gravitational tide waves will tear the arms apart and shred the pinwheel from the outside in. The Milky Way will then become and elliptical. This is nothing to fear though; scientists believe that our solar system will not be torn completely apart from the sun. Although, this is all theory.
As I said at the beginning of this paper, I have discovered a lot of things that most will never know, and most that I won’t be able to correctly define a year from now, I’m sure. But what I do know is that as I sit here writing this, I have, in fact, not quenched my curiosity. I’ve only made it all that much worse. And somehow, I don’t think that’s a bad thing. I do, however, still believe I am in way over my head!
Formation of the Milky Way, The E.J. Alfari and A.J. Delgado (1995)
Milky Way, The G.L. Vogt (2002)
17 August 2004 – Press Release European Southern Observatory
University of Oregon Astronomy 122
University of Maryland – West Baltimore
No comments:
Post a Comment