Could a Nearby Supernova Bring The Apocalypse?

This week, astronomers reported the brightest star explosion in our own galaxy and were all thrilled by the size and amount of light that the most spectacular supernova ever recorded had produced.

Surely, they would be thrilled to see another explosion even closer to our solar system, like perhaps the star Eta Carinae, one of the biggest and intrinsically brightest stars in our own Milky Way galaxy. This star is actually pretty close to us, in terms of space distances, being merely 7,500 light-years away from Earth. Most astronomers believe the star isn't posing any danger...

But what would happen if a supernova were to blow up as close to us as Eta Carinae, or even closer?

First of all, we wouldn't even know it until it would be too late. Why? Because we wouldn't even see it coming. Let's look at some numbers:
1 - Eta Carinae is 7,500 light-years away from Earth.
2 - A light-year is the distance light travels in a period of one year.
3 - For humans to actually "see" the supernova would mean that our eyes would have to perceive light originating from that event.
4 – We would only see the light produced by the blast only after it traveled the entire distance of 7,500 light-years.

To cut a long story short, Eta Carinae could have exploded already and we wouldn't know it, since it takes 7,500 years for the light of the explosion to reach us. Visible light travels at the same speed as any other deadly radiation, so we would start feeling the effects of radiation from the first moment we see the light.

How could a supernova affect us?

In many ways. We wouldn't have to worry about debris, since almost all the ejected material will slow down before it reaches us. What we should worry about is the gamma-ray burst. That would be the likeliest cause of a supernova nightmare, and there wouldn't be much we could do about it.

Until astronomers prove to be able to predict such a stellar event, giving us enough time to build, say, underground cities, we will just have to wait.

Now, I'm not trying to scare you, and you’d probably say "this couldn't happen to us." But perhaps it did, early in the Earth's history... A couple of years ago, a research published in the Astrophysical Journal Letters launched the idea according to which a gamma-ray burst lasting just 10 seconds could have caused the Ordovician mass extinction, 440 million years ago.

The Ordovician-Silurian extinction event was the second largest of the five major extinction events in Earth's history in terms of percentage of genera that went extinct. It occurred approximately 444–447 million years ago and killed around 49% of all fauna.

According to scientist from the University of Kansas and NASA, the extinctions may have been caused by a gamma ray burst that was caused by a star exploding into a supernova just 6,000 light years of Earth, in a nearby arm of our galaxy.

It's a good thing Eta Carinae is 7,500 light years away, right? The distance and effects ratio are not too optimistic, even with the extra 1,500 light years...

What could happen if a gamma ray burst were to hit Earth?

Well, a ten-second burst would be enough to strip the Earth's atmosphere of half of its ozone almost instantaneously, exposing surface organisms, including the plants responsible for planetary photosynthesis, to a massive dose of ultraviolet radiation.

Another dangerous effect would be the fact that nitrogen atoms dissociated from ozone molecules would go on and form NO2 molecules, a reddish brown toxic substance that absorbs sunlight to produce a rapid cooling of the Earth's surface, much like a nuclear winter, setting off a new ice age.

For now, astronomers say that an eventual explosion of Eta Carinae would not pose an immediate threat to our planet. Maybe if and when such an extinction level event were to occur, we would have developed the technologies to protect us from this threat. Or at least to allow us to "abandon ship" and settle on other worlds in this galaxy.

Until then, most people have many other things to worry about, so I suggest you do the same and enjoy the time you have left. After all, who knows, the Apocalypse could come earlier mainly because of manmade pollution, or from other causes. Or maybe it won't come at all...