A recent study has added a potential new threat: a special type of supernova that can destroy a distant planet’s ozone layer years after the initial explosion.
When giant stars die in massive explosions called supernovae, they temporarily become some of the most luminous objects in the universe. A single supernova can outshine the combined light of hundreds of billions of stars.
For example, the neighboring star Betelgeuse is going to explode at any moment. This is an astronomical “anytime”, that is, sometime within the next few million years. Although the star is more than 600 light years from us, when it goes supernova it will be the brightest object in our sky, second only to the Sun. Betelgeuse will be visible during the day and will outshine the full moon. For a few weeks, at the height of the explosion, it will be so bright it will cast shadows in the middle of the night.
Despite its eerie brightness, the visible light portion of a supernova represents only a small fraction of all the energy emitted. Also, although intense amounts of visible light can cause blindness, they don’t have many other serious effects. Of more concern is the high-energy radiation associated with the supernova, usually in the form of X-rays and gamma rays.
The effects of X-rays
High-energy radiation from a supernova can catalyze oxygen, stripping Earth’s protective ozone layer. Without the ozone layer, life on our planet’s surface would suffer from the full blast of ultraviolet radiation from the sun, potentially triggering an extinction event.
The burst of radiation occurs in the first few seconds of a supernova, but an even greater threat comes later. Cosmic rays, subatomic particles accelerated to nearly the speed of light, erupt hundreds or thousands of years later. They carry with them a significant fraction of the total supernova energy, and they can also strip away layers of ozone and leave a planet’s surface at the mercy of deadly radiation.
These phenomena may have occurred in the past. Analysis of lunar regolith and deep sea cores reveals the existence of substantial amounts of iron-60, a radioactive isotope of iron that only occurs in supernovae. The presence of iron-60 suggests that Earth was hit by supernova ejection just a few million years ago.
Based on the threats posed by gamma rays and cosmic rays, astronomers have already concluded that we are relatively safe: there are no nearby supernova candidates that could pose a threat to life on Earth.
But astronomers have discovered a potential new danger, which they describe in a article published on arXiv in October: AN a certain type of supernova can release an additional form of deadly radiation over long distances that poses a grave danger to Earth-like planets.
This special type of supernova occurs when a star nearing the end of its life is surrounded by a thick disk of material. After the initial explosion of the supernova, a shock wave forms that impacts against the disk. The shock wave heats the disk to incredibly high temperatures, causing the disk to emit large amounts of X-ray radiation.
This radiation can carry large amounts of energy and travel extremely long distances. In the recent study, astronomers discovered that the brightest X-ray supernovae can overwhelm a planet’s ozone layer, depleting it by up to 50%, which is more than enough to trigger an extinction an incredible 150 years away. distance.
That kind of supernova would be a killing blow. Months or years after the initial explosion, a vulnerable planet would be bombarded by X-rays. Then, hundreds or thousands of years later, the planet would be destroyed. Then, hundreds or thousands of years later, cosmic rays would finish the job before the biosphere had a chance to recover and replenish its protective shell.
Fortunately, Earth is still safe, as we don’t know of any nearby X-ray supernova candidates. But this new study places further limits on the galactic habitable zone, the region of each galaxy that can support life. In the outer reaches of a galaxy, star formation is too low to accumulate the necessary ingredients for rocky planets. But dense cores, where stars live and die in a frenzy, are also deadly, because frequent supernovae flood their surroundings with radiation.
The new study shows that the inner edge of the galactic habitable zone is likely farther from the galaxy’s core than previously assumed. However, despite being hit here and there, Earth is in one of the safest neighborhoods in the entire galaxy.
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