Monday, August 24, 2009


Sorry for the long hiatus from posting on my blog. I'm gonna try to be more regular with this. Jennifer wanted me to explain galaxies after my last post so I will try to do just that.

Too fully understand galaxies you have to start with something even more mind boggling: the Big Bang. When the big bang erupted roughly 13 to 14 billion years ago it sent all of the contents and mass of our universe flying outwards in every direction. This mass, the entire existence of our universe, was no where near as spread out as it is now and was instead very condensed and hot, almost entirely gaseous in nature (almost all hydrogen at the very beginning). The widely excepted belief is that this superheated gas had pockets where it was more massive and condensed than in other places. After what is believed to be about 300,000 years these areas called proto-galaxies, due to gravity, had accumulated enough mass (and coincidentally heat) for the process of nuclear fusion to begin and making them the first stars. Now these stars were nothing like our sun. They were enormous, much, much larger and hotter than our quaint little star. The problem with stars this big and hot is that they live very short lives (only a few million years, unlike a star the size of our Sun which will exist for many billions of years).

To understand this next part you need to understand a little about nuclear fusion. Nuclear fusion occurs in a star when it reaches a high enough temperature to fuse the element hydrogen into helium. After it has used up all of it's hydrogen if it's massive enough it can fuse helium into carbon. If it is still even larger it can fuse carbon into neon, then neon into oxygen, and then oxygen into silicon. However the process ends when the star tries to fuse silicon into iron. This is impossible and the star will gravitationally collapse, resulting in a massive explosion (the largest in the universe) called a supernova.

These short lives end in extremely violent ways, that of a supernova. When these first stars went supernova they created the heavier elements that we are familiar with, like the carbon that we are mostly made out of and the nitrogen and oxygen that we breath.

To understand how this process resulted in the first galaxies being formed you have to understand a little bit about the most mysterious things in the universe: Black Holes.

When a super-massive star explodes into a supernova not all of that mass is expelled into the space around it. Some of that star reached such a critical mass that its very own gravity sucked inwards and became so dense that it formed a black hole. A black hole is something that is so densely pact into one place that its gravity has reached a point where nothing in the universe, not even light can escape.

These enormous black holes that were created continued to gather material and gas from the space around them until they had accumulated matter in an orbit around it (not unlike the Earth's orbit around the sun) that stretched for thousands of light years in each direction. This matter eventually formed into more stars and planets revolving around those stars until eventually, millions and billions of stars orbited these supermassive black holes. This is how galaxies were formed, at least in some theories.

Currently astronomy is being completely overhauled and changed to encompass the theory of dark matter which is a whole other topic that I have not read up on enough to fully understand at this time. However, this theory could completely change all current notions of what the universe is composed of and how we perceive it to work. Current estimation put dark matter as high 90% of the makeup of galaxies (mindblowing right?!?!).

Over time galaxies have combined and become larger. Some of them have burned out and died and some of them are producing new stars on a regular basis. Some of them are rich in plenty of elements and some of them are absent of many heavier elements like metals.

There are believed to be over 100 billion galaxies in the known universe. Of these galaxies almost all of them (95%) are close neighbors to another galaxy. For instance, we (the milky way galaxy) share the neighborhood with the galaxy Andromeda and our little cluster is a part of a much larger neighborhood of galaxies as well. All of these galaxies close by are the same age as the milky way, showing that we all came from the same enormous cloud of matter.

If I didn't answer what you wanted to know just ask me and I would be happy to add to this. :)