Exploding Stars
Milky Way - Artist's Representation Exploding stars are known as nova or novae. But a nova does not account for all exploding stars, because there are also supernova and luminous red nova that are known and maybe other things that are not know about yet. I remember when I was a teenager I actually saw a nova in the sky that was so bright it lasted for about 3 days and could be seen in the daytime. I never forgot that event, because it was so unusual. I think that most of us know we live in a galaxy called the Milky Way. It is a spiral galaxy and we are lucky enough to live way out on one of the arms, away from a lot of the action that could be disastrous to us. It is estimated that there are about 30 to 60 nova per year in our galaxy. Astronomers only discover about 10 of these every year. You wouldn't want to be too close to one of these explosions, because they could be deadly, that is why it is so good to be located where we are. A nova can be so bright that even though there are huge distances between galaxies, we sometimes see the light from a nova from another galaxy. What is amazing about this is that the star is long gone and could have exploded even billions of years ago and the light is just reaching us now. I find it amazing to think of things in these terms. It also makes one aware of the fact that everything we see in the sky that is outside of our solar system could have vanished over 4 years ago minimum. I say this because the closest star to us is Proxima Centauri and that is about 4.2 light years from earth. So here we are in a solar system and we think that everything that we see in the night sky is really there, but much of it and even all of it, may not even exist anymore. When we talk about nova there are different types of these explosions. There are the type that rapidly go to extreme brightness and decline to about 1/16 of that within 100 days, this is called a fast nova. There are slow nova where the nova declines about 3 magnitudes in 150 days or more. There are nova called very slow nova that stay at their very bright light for decades then fade slowly and there are even nova that recur. These actually explode more than once. Nature is truly strange isn't it?
Nova If anyone watches the History Channel on television they have to know by now that there are all sorts of doomsday scenarios involving something called a gamma ray burst. These bursts can be deadly over distances so great that they boggle the mind and they seem to be related to huge explosions. A typical burst is very short, only lasting a few seconds, but in those few seconds a narrow beam is usually emitted from a supernova. It is thought that this is formed when a star collapses into a black hole. This may not be the only time a gamma ray burst is released. It is thought that it might also happen when two binary neutron stars merge. As you can see this is not a phenomenon that is fully understood. In the few seconds of a gamma ray burst you can get more energy than our sun releases in 10 billion years. There are not many of these types of events, if there were there would be no possibility of life anywhere. The only ones we have observed so far are outside of the Milky Way. It is a lucky thing for us that this is true, because scientists believe that if a gamma ray burst was to take place in the Milky Way, that could end life on Earth. Here is one of the problems however. There could have been a burst already and the gamma rays haven't reached us yet since they only travel at the speed of light. That is the uncertainty that we live with when we are talking about such vast distances, distances so great that it could take light millions and billions of years to reach us. The Milky Way is approximately 100,000 light years across. As I said we are on one leg or spiral. If gamma rays started coming toward us from an explosion in the Milky Way at the other end, it could take maybe 80,000 years or more before we even knew it. On February 19, 2009, NASA's Fermi telescope detected the most powerful gamma ray blast ever discovered. The scientists at Fermi stated that blasts at these levels are poorly understood. The explosion was in the constellation Carina. So how powerful was this blast? It was estimated that it was more powerful than the blast from over 9,000 supernova. It was calculated that the gamma rays moved at 99.9999 percent the speed of light. One strange thing about this blast was that there was a 5 second delay between the highest energy emissions and the lowest. This had only been seen once before. One scientist stated, "It may mean that the highest-energy emissions are coming from different parts of the jet or created through a different mechanism,"
Supernova There is quite a difference between a nova and supernova. A supernova is a stellar explosion that can produce more energy than an entire galaxy for a brief amount of time. A nova is a nuclear explosion. It is caused by accretion of hydrogen onto the surface of a white dwarf star. The hydrogen ignites and starts the process of runaway nuclear fusion. As you can see both are incredibly enormous explosions, but the supernova is so powerful that it is like a hydrogen bomb compared to a conventional bomb. If there are more powerful explosions in the universe, they have not been discovered yet. This is not to say that they don't exist. How do we know that there isn't something that might cause an entire galaxy to explode? For all we know, a supernova explosion under certain rare and extreme circumstances might be able to trigger a chain reaction. Space is far from being the empty place that was first pictured in the SciFi movies of the 1950s. Can you imagine you are flying in a spaceship and you get hit by a powerful gamma ray beam? What if micro particles hit your ship or even radiation released by a star? There is the chance that you could even be hit by a meteor that might be traveling so fast that by the time you detect it, it would be too late. There are magnetic and gravity waves that might draw you too close to objects, such as a black hole or neutron star. Space is actually an extremely dangerous place for many reasons and some of them are probably not known about yet. |
