Avi Blizovsky
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There is a wide variety of potential threats to the planet and its inhabitants - from global warming to a deadly asteroid strike or nuclear war, so it's nice to hear that at least one danger is decreasing at least somewhat.
Since the seventies of the twentieth century, astronomers have estimated that there is a danger to the earth from the explosion of supernovae. Among the negative consequences of such an event - the sudden disappearance of the ozone layer that protects us. This miss will leave us exposed to space and then we will all be fried by our sun's ultraviolet radiation.
Such a massive supernova, you radiation is 8,000 light years away from us. It has doubled in brightness in less than 18 months recently.
Can gamma rays cause mass extinction of living things? Not all scientists agree on this. Most of them claim that only a physical asteroid could cause such an event, such as the one that wiped out the dinosaurs and over ninety percent of the living creatures and plants of their time, and whose impact crater was discovered in Mexico.
The researchers claim that at least one extinction event during the last hundreds of millions of years was ignited by a supernova, and this could happen again. However, new details emerging from recent calculations show that such accommodation is extremely rare.
The study, led by Neil Gehrels of NASA's Goddard Aeronautics and Space Administration, found that for a supernova to massively damage the ozone, it would have to occur within 26 light-years of Earth. Other data show that such an event occurs once every billion years.
This specific path to the mass extinction of life seems less likely than scientists have previously estimated,” Gehrles and his colleagues wrote in an article to be published in the March 2003 issue of the Astrophysical Journal.
The researchers built a detailed model of the chemical reactions that occur when the energy from such a supernova reaches Earth, and they also examined how this energy would survive the journey through space until it arrived here. The dangerous emission of the supernova includes gamma rays - the most energetic type of light, plus cosmic rays that come in the form of particles, explains John Cannizzo, another researcher at Goddard who participated in the study. The interaction of these particles and energy with the nitrogen in the atmosphere turns the n2 into nitrogen monoxide, and the ozone decomposes into oxygen. "When we connect all the components to a single picture of ozone depletion as a result of energy from space, we see that it is not something so serious.
The exact result depends on the sensitivity of many assumptions, but it's the best we have so far, says John Scalo of the University of Texas at Austin, who was not involved in the study but is familiar with it.
There are other negative effects to supernovae and other energetic astronomical events that were not considered in the current study. Other researchers have shown that exposure to high energy particles from space over time can cause mutations. Mutations are not always a bad thing. The scientists estimate that some mutations may benefit their owners or at least not hinder them from an evolutionary point of view. Another alarming event is the hypernova, which is also linked to the mysterious bursts of gamma rays in deep space. Astronomers believe that these are similar to supernovae, but they release a beam of concentrated energy that hits all the stars on the planet's axis of rotation, and which, if this axis happens to face Earth, could cause trouble.
Such an event, says Gehrels, occurs once every two hundred million years in our galaxy, usually far from Earth.
According to the data from the Instrument and Transient Source Experiment (BATSE), which monitors gamma ray bursts, which according to the note originate from hypernovae, occur in space (in all galaxies together, not necessarily for the Milky Way) at a rate of 500 per year, that is, between one and two bursts per day, all of this in the visible universe About 14 billion light years.
Assuming there are 100 billion galaxies in space, this rate translates to one gamma-ray burst within a galaxy every 200 million years. Because the energy is so concentrated compared to a normal supernova, a hypernova can be harmful to life on Earth even at a much greater distance from a supernova. Among the scientists studying these bodies is Prof. Arnon Der of the Technion (see link to the Technion astrobiology article).
For information on Space.com
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