Stars, Black Holes, and the Universe

Michelle, I was rather delighted to read about your outing to the observatory. I know a bit about Astronomy, and I can give you some interesting facts. Unfortunately, I ended up writing so much, I figure I might as well make a proper post with pretty pictures.

Stars, Black Holes, and the Universe

The most astonishing idea really is how truly vast space is. If you shrink Earth down to the size of a marble, the nearest star other than the Sun (called Alpha Centauri) would be 200 km away! It lies about 4 light years away, meaning that at the speed light moves (300 million meters per second), it would take 4 years to reach us.

The Andromeda Galaxy (Disk shaped, very like our own)

Stars are formed from very dense dust clouds that are literally enormous (many, many times bigger than our solar system). You can think of it as the dust cloud collapsing on itself (from pressure), and forming this ball. The ball ages (or burns) and as it burns, it loses precious materials. At some point, it has burned up so much material that it starts to self destruct -- and goes supernova. But this only happens to big stars. Most little stars will just burn out and become a white dwarf and later, a black dwarfs (essentially a dead star). In fact, the Sun will one day become a white dwarf (it's too small to go supernova).

Formation of Stars

Now, if you take a massive star near the end of its life, you get something very interesting. Stars are alit because they are always burning something at their cores. What happens after they burn for a long time is that the core starts shrinking due to gravity. So the core shrinks and shrinks...until it doesn't shrink anymore (why this occurs, is a bit too long of an explanation).

Then suddenly this core, which is about the size of the Sun, collapses within a fraction of a second. Imagine the Sun, shrinking to the size of a city...in less than a second! This produces the supernova, and the remnants is what's known as a neutron star. The key word here is density. If you were to take a teaspoon of the stuff a neutron star was made of, it would weigh about as much as a mountain.

A Supernova and Neutron Star

Now, if your original star was big enough, what happens is that this neutron star continues to shrink...and shrink. Until, well, it shrinks to a point. So what happens now?

Well, you have a big problem. You have compressed the mass of (several) Suns into something smaller than a dust particle. So what happens it that gravity is so incredibly strong near this point that even light is sucked in. In fact, no light can escape from this point. This is what is known as a black hole. Black holes are very interesting objects, mainly because of the fact that anything that is remotely near it is sucked right in. In fact, black holes literally eat up stars for breakfast, lunch, and dinner. The result when you munch a star is an output of energy.

Now, if you take a look at the center of our galaxy, you see a big energy output (lots of light, explosions, supernova, etc.). It's hypothesized that at the very centre of our Galaxy, lies a black hole, munching up all the stars around it.

A Black Hole's Breakfast

Okay, so we have the Earth. The Earth is near the Sun (a star), which is inside our Solar System (consisting of a bunch of planets). The Solar System is contained in the Milky Way, which is our galaxy. In each galaxy, there are about 100 million to one trillion stars. And how many galaxies are there in the Universe? Only about one hundred million.

Astronomers have actually managed to find ways of 'looking' at far away galaxies. In fact, the farthest galaxies they've managed to detect lie about 14 BILLION LIGHT YEARS away. This is actually the hypothesized age of the Universe! So in fact, when the astronomers see these galaxies, they are gazing 14 billion years into the past...

So who knows what the Universe is really like right now!


Side note: I took a lot of liberties to make this as short as possible. So there is a fair amount of inaccuracy. For example, there are many ways a star can die. Forming a supernova and neutron star is actually very, very rare -- albeit the most interesting path.