Science for Thought

Which Came First

Which Came First

This is not a chicken and egg joke. What I would like to discuss is the two competing theories about how galaxies were formed.

Why is this important?

The reason is simple. Knowing the answer would help cosmologists to understand how galaxies were formed and how early it happened. Galaxy formation is very important because without it we wouldn't be here.

First of all, all galaxies have a supermassive black hole in their centers. This has been proven for our Milky Way galaxy and several other galaxies. The question is: how did these supermassive black holes form and how early did it happen.
The basic building block of the universe is the galaxy. This is because a galaxy is the only place where stars can form, especially stars like ours. Galaxies are where hydrogen gas can be forced to condense to create a star. Our galaxy formed because of a supermassive black hole. This black hole has a mass millions of times the mass of our Sun.

How did the early universe form these supermassive black holes?

Two theories explain how this happened:

One theory claims that stars formed first and then formed into galaxies. In this theory the supermassive black holes came later as large stars went supernova and formed black holes that combined to create supermassive black holes. It was then that galaxies formed around these black holes. The problem with this theory is that there was not enough time for the black holes to grow to monster size in order to form the earliest galaxies. The evidence for this is that quasars, which are from supermassive black holes, have been found to be in very early galaxies that were formed only a few hundred million years after the Big Bang. Quasars are evidence of very early galaxies.

The second theory claims that supermassive black holes formed first and helped capture lots of hydrogen gas that eventually formed lots of stars. How could this happen? The theory is that very large stars that formed early after the Big Bang condensed down directly to black holes. This would suggest that the large stars never began to fuse and simply were overwhelmed by gravity. The collapse would result directly into a black hole. These stars were monster sized, at least a million times the mass of our Sun. These large black holes then were able to attract lots of gas that could then be used to create stars.

This is just a theory. However these early quasars are in galaxies that are not very big. Our Milky Way galaxy is a hundred thousand light years across, but these early galaxies are only a few thousand light years across. That means that these early galaxies have supermassive black holes that existed very early on, a clue that they came first.

A quasar is evidence for the existence of a supermassive black hole in an early galaxy. Our Milky Way was like this at one time. It had a quasar but now it has settled down from its early infant tantrums and is more mature. Super massive black holes that emit intense beams of energy out of their poles help create stars in an early galaxy. That's possibly how our star, the Sun, formed. In other words, a quasar from a supermassive black hole helped form us.

This is why cosmologists are more excited about the second theory. It helps explain the recent observation of early quasars.

You might ask then the question of how our galaxy grew so large. This is because big galaxies feast on their smaller siblings galaxies that formed nearby. The big galaxy acts like a bully and begin to attract these smaller galaxies, consuming them. These colliding galaxies are visible out there. As a matter of fact, our galaxy is still eating smaller galaxies. This process takes billions of years.

I like the second theory, but it still needs more evidence.

Thanks for reading.