Gamma-ray bursts are the most energetic and luminous explosions in the known universe. They typically occur when a dying, rapidly-rotating star collapses and becomes a black hole. During this collapse, a narrow beam of intense radiation is released at near the speed of light. In fact, the largest explosion ever recorded in the cosmos, this side of the Big Bang, was witnessed in April of this year and it was caused by a gamma-ray burst. The explosion occurred a staggering 3.7 billion light years away, so no worries to those of us on Earth. We are safe from this explosion which astronomers have termed the "Monster." Even at its extreme distance, instruments picked up five times more energy than the "blast from the past" as I like to call it, in 1999, the next largest gamma ray burst ever recorded.
To say these bursts are intense would be an epic understatement. A typical gamma-ray burst, which lasts no longer than a few minutes, releases as much energy as our sun will release over its 10 billion year lifespan! That is an incredible explosion.
Gamma-ray bursts are nature's form of the ultimate fireworks display. They last between a few milliseconds to upward of a few minutes. One could also say gamma rays are one of the most dangerous threats in the cosmos. If one were to occur in our astronomical neighborhood (within a thousand light-years from Earth) and be directed toward Earth, the effects could be devastating. With today's technology, scientists witness these bursts quite a bit, but with these events happening so frequently (300,000 times a year), could Earth ever be hit by one? Have we been hit in the past? A new theory says that the Earth may have been hit in the past, causing one of the top three mass extinctions on this planet.
Although the Cretaceous-Tertiary Mass Extinction (also known as the K-T Extinction) is the most well-known extinction event, which is believed to have wiped out the dinosaurs 65 million years ago, there was a much larger mass extinction event that occurred approximately 460 million years ago. This event is known as the Ordovician Extinction. This event wiped out 60-70 percent of marine species at a time when most life was still in the oceans. Although the exact cause is still unknown, there were two major events, separated by one million years, associated with this mass extinction. One is believed to have been related to high CO2 counts, which lead scientists to believe it was extreme volcanic eruptions that caused the 1st event. With the second event still undetermined, a new theory suggests it may have been a gamma-ray burst.
A small group of scientists put forth the hypothesis that a gamma-ray burst from a hypernova (at least 100 times larger than a supernova) within 1,000 lightyears, may have hit the Earth. An event lasting no longer than 10 seconds from that distance would be capable of burning through the ozone, and allow deadly amounts of ultraviolet light from the sun to penetrate the atmosphere, devastating most of the life on the surface. In 2003, when this theory was first proposed, there really was no way to test it, but that may have changed.
Wilfred Domainko, a physicist at Germany's Plank Institute, suggested that if a gamma-ray burst were to occur, it most likely would come from a globular cluster. A globular cluster is a group of stars close to each other wherein many dead stars exist. If those dead stars were to attract to one another and collide, that could create a gamma-ray burst. But could this occur so close to Earth? Domainko says odds are good that such an event could have occurred relatively close to Earth at least once within the last billion years.
In 2013, the Gaia Star-Mapper (learn more about it here
http://www.esa.int/Our_Activities/Space_Science/Gaia_overview) will be mapping the positions and velocities of all globular clusters, among other things. Once the data is collected, scientists will be able to extrapolate whether any of these clusters could have caused such an event to occur. What would be the effects of a gamma-ray burst on Earth? On the side of the planet facing the burst, there would be a brilliant sky, hundreds of times brighter than the sun, enough to cause permanent blindness. This brightness would not be from any actual explosion, but from the intense rays exciting the particles in the atmosphere, essentially an extreme form the aurora, except that the entire sky would be bright white. The energy delivered to the Earth's atmosphere would be equivalent to 100,000 megatons of nuclear explosions, and would cripple the ozone layer. With limited ozone, or no ozone, ultraviolet light would penetrate the atmosphere, a majority of crops would die off from burns, radiation poisoning and acid rain. Humans outside, in the path of this burst, would be instantly incinerated.
Humans surviving the initial burst would not be spared, however. The gamma-ray burst would not immediately affect those on the opposite side of the Earth, because gamma-rays do not penetrate through the planet. However, the indirect effects such as the acid rain, depleted ozone, and potential "nuclear winter" would lead to mass extinction over time.
Although the chances of this occurring are quite remote any time soon, it is possible. With an endless number of gamma-ray bursts going off in the cosmos, it would only take one nearby to send us back to the stone ages... or worse.
Currently, there is no way to stop this from happening, as these bursts occur at or near the speed of light. By the time we detect it through satellites, it would already have impacted our planet. As science continues to advance and we begin to learn about these incredible explosions occurring throughout the universe, perhaps we will discover some practical planetary defense. In the meantime, we can increase our understanding of these awesome and dangerous cosmic marvels.
Blog written by newest AccuWeather Astronomy new member Gregg McCambley
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