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Gamma-Ray Bursts

November 16, 2009 Leave a comment Go to comments

Gamma-ray bursts (or γ ray bursts for those of you who can read frat) have been making a bit of a splash in the science world lately. Within just a few days of each other, two articles showed up that really piqued my interest. One article shows that a recent gamma-ray burst proves that Einstein was correct, yet again, while the other article talks about the furthest and oldest gamma-ray burst ever discovered. Until these articles surfaced, I must admit that I was unaware of the existence of gamma-ray bursts. It’s not my fault, though, unless you have a really neat satellite telescope or are unlucky enough to have one go off relatively close to you, they’re not really something that concern us daily.

Gamma-ray bursts were first discovered in the 1960s. U.S. satellites were sent into orbit to detect gamma-rays. They were afraid that the USSR would be secretly trying to detonate nuclear weapons in space (again with the commies), and the satellites were used to detect such explosions. Since nobody was testing nuclear weapons in space, what the satelites did detect were gamma-rays signatures that didn’t match up with anything that current weapons were known to produce. Since these weren’t considered to be a danger, the signatures were quickly forgotten about, until more satellites were launched and more and more bursts were found. After a number of bursts were studied it was discovered that they were neither coming from Earth or the Sun, but from some cosmic source.

Now that it was known that the bursts weren’t coming from anything local, scientists began to theorize where they might be coming from. For decades a number of theories about gamma-ray burst origins came about, but none could be confirmed. Part of the problem was that gamma-ray bursts usually generate from very far away (usually on the scale of billions of light years), and are very hard to detect on visual levels. It wasn’t until the last ten or so years that technology has advanced far enough to really study the gamma-ray bursts.

As it turns out there are two types of gamma-ray bursts, long and short. Long bursts are any bursts that are longer than 2 seconds. They are usually observed in rapidly star-forming galaxies and are associated with the death of massive stars. Short bursts exist for no longer than two seconds are usually found in areas with little or no star formation. This is what also makes them distinct from long bursts, since they have no known association with massive stars. It’s theorized that they’re generated by the merger of binary neutron stars.

Long gamma-ray bursts are so energetic that it’s theorized that they would be similar to the energy that would be released if the Sun were converted entirely to radiation, otherwise known as the rest-mass energy. However, since nothing in the universe is capable of producing this much energy in such a short time, it’s theorized that the bursts are concentrated in beams instead of being released spherically. The beams are thought to produce when the rapidly rotating stars collapse into a black hole. As matter falls into the now rapidly rotating black hole, a disk is created and the gamma-rays shoot out from the rotational access.

This also explains why gamma-ray bursts are so rare, because if the beam isn’t aimed at Earth, we simply can’t detect it.  Another reason for their rarity is that the genesis of these bursts is thought to originate from a very specific type of star. These stars are extremely massive, with a low metallic content. Most of the stars in the milky way and neighboring galaxies have a high metallic content. Which is a good thing because a gamma-ray burst in the milky way and focused at Earth would have a huge ecological impact. Gamma-rays are a type of ionizing radiation and are often deadly to organisms.  Beyond that, a gamma-ray burst hitting the atmosphere would cause  a large amount of nitric oxide, which would destroy a significant chunk of the ozone layer. Such a burst is thought to be the cause of one of Earth’s mass extinctions, the Ordovician-Silurian extinction which happened 447 million years ago.

Despite the rarity of such bursts being detectable by us, we’re still able to detect about one per day. Considering that for a galaxy that’s about the same size as the milky way, the frequency for a gamma-ray burst is only one every 100,000 to 1,000,000 years, it’s amazing that we’re able to detect any at all. The fact that we do just goes to show how vast and how full and how old the universe really is. It’s almost frightening to think about.

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  1. April 14, 2010 at 7:33 pm

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