Astronomers using data from NASA's Chandra X-ray Observatory and other telescopes have identified a new threat to life on planets like Earth: a phase during which intense X-rays from exploded stars can affect planets up to 160 light-years away.
However, Earth is not in danger of such a threat today because there are no potential supernova progenitors within this distance, according to the study. But it may have experienced this kind of X-ray exposure in the past, says Chandra X-ray Observatory.
This newly found threat comes from a supernova's blast wave striking dense gas surrounding the exploded star. When this impact occurs it can produce a large dose of X-rays that reaches an Earth-like planet months to years after the explosion and may last for decades. Such intense exposure may trigger an extinction event on the planet.
For an Earth-like planet, this process could wipe out a significant portion of ozone, which ultimately protects life from the dangerous ultraviolet radiation of its host star. It could also lead to the demise of a wide range of organisms, especially marine ones at the foundation of the food chain, leading to an extinction event.
After years of lethal X-ray exposure from the supernova's interaction, and the impact of ultraviolet radiation from an Earth-like planet's host star, a large amount of nitrogen dioxide may be produced, causing a brown haze in the atmosphere. A "de-greening" of land masses could also occur because of damage to plants.
A new study reporting this threat is based on X-ray observations of 31 supernovae and their aftermath — mostly from NASA's Chandra X-ray Observatory, Swift and NuSTAR missions, and European Space Agency's XMM-Newton — show that planets can be subjected to lethal doses of radiation located as much as about 160 light-years away.
Although the Earth and the Solar System are currently in a safe space in terms of potential supernova explosions, many other planets in the Milky Way are not. These high-energy events would effectively shrink the areas within the Milky Way galaxy, known as the Galactic Habitable Zone, where conditions would be conducive for life.
Because the X-ray observations of supernovae are sparse, particularly of the variety that strongly interact with their surroundings, the authors urge follow-up observations of interacting supernovae for months and years after the explosion.
The paper describing this result appears in the April 20 issue of The Astrophysical Journal.
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