To evaluate how close a supernova would have to be to cause serious damage to Earth, we must first look at a supernova’s destructive capabilities. When the bright star Betelgeuse explodes, a spectacular sight will emerge. The star’s explosion, known as a supernova, will be brighter than any planet and nearly as bright as the full Moon. It can be seen during the day, and at midnight you can read a book in its light. Like all supernovae, it will last several months before fading.

But it won’t be dangerous. For this, it would have to be much closer; Betelgeuse is approximately 650 light-years away. So, are there any stars that pose a threat to us? To estimate how close a supernova would have to be to cause serious damage to Earth, we must take into account the destructive capabilities of a supernova.

The first is the shock wave caused by the explosion itself. But believe me, if you’re close enough to a supernova to worry about a shock wave, then you’re close enough to the pre-supernova star to have received a lethal dose of radiation, and you should have left it a long time ago. .

Then visible light. Even though it is impressive and blinding, it will not be a factor that will harm our planet.

Speaking of energy output, the vast majority of the energy released by a supernova is in the form of neutrinos, ghost particles that barely interact with matter. In fact, trillions of neutrinos are passing through your body right now, and I’m sure you don’t even notice them. So even if you get supernova-sized neutrinos, you won’t worry.

What about other wavelengths of light, like X-rays and gamma rays? The good news is that supernovae do not produce large amounts of high-energy radiation. But the bad news is that this is only in relative terms. On any reasonable absolute scale (like how many gamma rays will pass through the atmosphere) that’s still a ton of high-energy radiation.

And finally there are cosmic rays, particles reaching almost the speed of light. Supernovae are capable of producing large amounts of cosmic rays that can cause serious damage.

blast radius

So why are all these X-rays, gamma rays and cosmic rays so harmful to the Earth? These forms of radiation are effective enough to break down molecular nitrogen and oxygen. These elements in the Earth’s atmosphere prefer to float as molecules. But once they fall apart, they come back together in interesting and fascinating ways; For example, they form various nitrogen oxides, including nitrous oxide, i.e. laughing gas, which leads to ozone depletion.

Without the ozone layer, Earth is vulnerable to the sun’s ultraviolet rays. This doesn’t just mean faster tanning, faster burns, and higher skin cancer rates. Photosynthetic microorganisms such as algae become vulnerable. They basically prepare and die. Since they form the basic layer of the food chain, the entire ecosystem collapses and mass extinction occurs.

For supernovae, which tend to occur in our galaxy, the dying star would need to be around 25-30 light-years from Earth to remove at least half of the ozone layer, which would be enough for all the ill effects mentioned above to occur. things

And here’s some good news to help you sleep at night: There are no known supernovae within 30 light-years of Earth. The closest candidate, Spica, is about 250 light-years away, and there is no star that will become a supernova candidate in its lifetime and come within 30 light-years of Earth. So at least we’re safe on that front for now.

But over a longer period of time, things start to get more interesting because they start to deal with entities that pose a risk to the existence of entire biospheres.

One interesting thing is that our solar system is currently entering the Orion spiral arm of the Milky Way, and spiral arms are known for their high rates of star formation (which is why they tend to stand out in images). But higher rates of star formation mean higher rates of stellar death; That means there’s a better than average chance of getting too close for comfort in the 10 million years we’ll have our arms crossed.

When you take all these factors into account, you get estimates of a potentially deadly supernova exploding several times every billion years. In fact, some astronomers believe that a nearby supernova caused a mass extinction that killed 75% of all species 360 million years ago.

Don’t sleep on this

But there is a small caveat: This analysis is only valid for typical, ordinary supernovae. There is also a special case where a dying star is surrounded by a thick layer of dust. When a supernova shock wave hits this dust, it emits a stream of X-rays, followed centuries later by a cosmic ray burst. This is a terrible blow: X-rays can travel more than 150 light-years and weaken the planet’s atmosphere, and after a few hundred years cosmic rays will finish the job.

In addition, there are Type Ia supernovae triggered by white dwarfs, which are superdense remnants of low-to-medium-mass stars like the Sun, accumulating material from an orbiting satellite. But white dwarfs tend to be small and faint, so they are much harder to detect and their collapse into a supernova is much more random. One day they just hang out, the next day they turn into nuclear hell.

Fortunately, the closest candidate is the double white dwarf IK Pegasi, which is safely located about 150 light-years away.

But before you get too complacent, you should be aware of gamma-ray bursts that are the result of neutron star-hypernova mergers. They are much more dangerous because they are incredibly powerful and their explosive energy is concentrated in narrow beams that can penetrate more than 10,000 light-years across the galaxy. Because gamma-ray bursts occur much further away than supernovae, they are more difficult to predict and plan for.

Rest in peace!