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Credit: NASA/CXC/Univ. of Illinois
A supernova explosion signifies the death of a star, and these events can be so energetic they outshine entire galaxies for a short time. So, it should come as no surprise that these events can be dangerous for nearby stars. A new analysis of supernovas explores yet another way these stellar detonations could damage nearby planets. Even if a world survives the initial radiation burst, the X-rays that follow could fry the atmosphere.
A supernova can occur for several reasons, but the largest and most dangerous are known as Type II. After exhausting their nuclear fuel, old stars can no longer withstand the force of their crushing gravity. The structure collapses, resulting in a massive release of energy. The star’s outer layers are blown outward, along with a burst of ionizing radiation that can seriously impact nearby solar systems. Supernovas also send a shower of cosmic rays that could take thousands of years to reach nearby worlds. According to the University of Illinois researchers, between those two events is the possibility that X-ray emissions could wreck the atmosphere of Earth-like worlds.
As massive stars approach a supernova event, they cast off their outer layers, forming a cocoon of dust and gas. The team used observations of 31 supernovas using X-ray instruments like Chandra, Swift-XRT, and XMM-Newton to understand what happens when the blastwave reaches this bubble of stellar material months or years after the event. The study points to a previously unknown burst of X-rays that could affect planets up to 160 light-years away.
The X-ray emissions from a supernova probably wouldn’t reach the surface of an Earth-like world, but they would trigger chemical reactions that consume all the ozone in the planet’s atmosphere. This would then expose the surface to intense ultraviolet radiation capable of killing most living creatures on land and in shallow water. The result would most likely be a mass extinction.
The good news is Earth appears to be safe from this outcome as it is from the more immediate effects of a supernova. The closest star that looks set to detonate is Betelgeuse, some 530 light-years away. Earth sits within the “Local Bubble,” a region of low-density hot gas surrounded by a shell of cold gas. This region may have been bored out by ancient supernovas, but we don’t know how close Earth was to these events. Earth has at least some exposure to ancient stellar explosions, as evidenced by iron-60 isotopes in deep-sea rocks.
Since the energy output of supernovas can vary so much, the team recommends additional work to understand the safe distance for X-ray exposure better.
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