(ORDO NEWS) — Supernovae are bad news. They can destroy the biosphere and flood planets with deadly radiation.
And now, according to a recent study, a new potential threat has emerged: a special type of supernova that could destroy the planet’s ozone layer years after the initial explosion.
When giant stars die in powerful explosions called supernovae, they temporarily become some of the brightest objects in the universe. One supernova can outshine the light of hundreds of billions of stars.
In comparison, the nearby star Betelgeuse could explode any day now. (This astronomical “any day” means the next few million years).
Even though the star is more than 600 light-years away, when a supernova occurs, it will become the brightest object in our sky, second only to the Sun.
Betelgeuse will be visible during the day, shining brighter than the full moon. For several weeks, during the peak of the explosion, it will be so bright that it will cast shadows in the middle of the night.
Despite the frightening brightness, the visible light of a supernova represents only a small part of the total energy released.
In addition, intense amounts of visible light can cause blindness, but have no other serious consequences.
More worrisome is the high-energy radiation associated with a supernova, usually in the form of x-rays and gamma rays.
High-energy radiation can catalyze oxygen, depriving the Earth of its protective ozone layer.
Without an ozone layer, life on the surface of our planet would be exposed to the full effects of the Sun’s ultraviolet radiation, which could lead to extinction.
A radiation explosion occurs within the first few seconds of a supernova, but an even greater threat comes later.
Cosmic rays, which are subatomic particles accelerated to almost the speed of light, eventually break out of the whirlpool after hundreds or thousands of years.
They carry with them a decent share of the total energy of a supernova, and can also destroy the ozone layer and saturate the surface of the planet with deadly radiation.
Such events may have happened in the past. Analysis of lunar regolith and deep sea cores has revealed significant amounts of iron-60, a radioactive isotope of iron produced only in supernovae.
The presence of iron-60 suggests that the Earth was hit by a supernova just a few million years ago.
Based on the threat posed by gamma rays and cosmic rays, astronomers have already concluded that we are relatively safe: there are no supernova candidates nearby that could pose a threat to life on Earth.
But astronomers have discovered a new potential danger, which they described in an database in October: A certain class of supernovae could emit an additional, far-reaching form of deadly radiation that poses a serious threat to terrestrial planets.
This special class 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 a supernova, a shock wave is formed that crashes into this disk.
The shock wave heats the disk to incredibly high temperatures, causing the disk to emit large amounts of X-rays.
This radiation can carry large amounts of energy and travel extremely long distances. In a recent study, astronomers have found that the brightest X-ray supernovae can destroy a planet’s ozone layer, depleting it by 50%, more than enough to cause an extinction event at an incredible 150 light-years away.
Shrinking galactic habitable zone
Such supernovae can deal a fatal blow. Months or years after the first outbreak, the vulnerable planet will be emitted by X-rays.
Then, after hundreds or thousands of years, cosmic rays will come and finish their work before the biosphere has had time to recover and replenish its protective layer.
Fortunately, the Earth remains safe as we do not know of any X-ray supernova in the vicinity. But the new study puts additional limits on the galactic habitable zone, the region in every galaxy where life can exist.
In the farthest corners of the galaxy, star formation is too scarce to create the necessary ingredients for rocky planets.
But dense cores, where stars live and die at a frantic pace, are also deadly, because frequent supernovae flood the surrounding space with radiation.
A new study shows that the inner edge of the galactic habitable zone is likely further from the galaxy’s core than we previously thought.
However, despite being hit here and there, Earth is in one of the safest areas in the entire galaxy.
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