What Will Happen When Betelgeuse Goes Supernova?

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When Betelgeuse goes Supernova what will be the effects on Earth (not just the radiation but also the ejected gas shell)? originally appeared on Quora: the place to gain and share knowledge, empowering people to learn from others and better understand the world.

Answer by Corey S. Powell, former editor in chief of Discover, on Quora:

Betelgeuse has inspired a lot of astronomical scare-stories because it is a nearby red giant star that is expected to explode soon as a powerful supernova. What these stories often gloss over is that “nearby” and “soon” are relative terms. The way astronomers use them is quite different from the way we use those words in everyday conversation.

First, let’s look at “soon.” Astronomers estimate that Betelgeuse is approximately 10 million years old, and it began expanding into a red giant 40,000 years ago. That means it has begun nuclear fusion of helium in its core, creating oxygen and carbon and starting down the pathway to core collapse and eventual supernova detonation. Exactly how long it will take for that to happen is unknown; astronomers can only make estimates using models of stellar evolution. Those models, in turn, depend on Betelgeuse’s mass and rotation period, both of which are imprecisely known.

If Betelgeuse is almost 20 times as massive as the Sun, as most studies indicate, then it will explode sometime within the next 100,000 years, leaving a celestial splatter similar to Cassiopeia A (shown here). It’s more likely to blow up later in that time-frame, but it’s not impossible that it could explode tomorrow. Still, even if you assume that an explosion could happen randomly any time within that period, the odds of Betelgeuse exploding in your lifetime are less than 0.1%.

Then again, if Betelgeuse is closer to 15 times the mass of the Sun, as implied by a few other studies, and if it is rotating slowly, then it could take a million years or more to go supernova. In that case, the likelihood that you will live to see Betelgeuse go boom is a good, solid zero.

Now, let’s look at “close.” It’s not so easy to measure the distance to a bright red giant star like Betelgeuse. Different methods give answers ranging from 520 light years to nearly 700 light years, about 150 times as far away as Alpha Centauri. (Betelgeuse looks bright in our sky because it is so intrinsically large and luminous, as shown in this

illustration.) Even at the low end of the distance estimates, Betelgeuse is too far away to do significant damage to Earth. As
Charlie Kilpatrick explains, the material ejected directly by the Betelgeuse supernova will have expanded and cooled to insignificance long before it reaches Earth.

Radiation from the Betelgeuse supernova will certainly have some measurable effects on Earth’s environment, but probably only a minor impact on life. Betelgeuse is too far away to significantly ionize Earth’s atmosphere, for instance. One way to evaluate the risk is to look at the consequences of past nearby supernovas. It’s not easy to find evidence of them, which is one strong indication that only the very closest supernovas present much of a risk.

A recent study claims to find chemical evidence of two supernova explosions between 1.7 million and 3.2 million years ago. These explosions allegedly happened on the order of 300 light years from Earth, meaning they hit us with radiation 4 times as strong (give or take) as what we’d expect from Betelgeuse. There’s no clear sign that they had any effect on life, however. It’s possible they caused a period of climate cooling, but it’s also possible that the changing climate was completely unrelated. At any rate, there was no mass extinction during that era.

Statistically speaking, supernova explosions should occur within 100 parsecs (300ish light years) every 2 million–4 million years. Whatever effect they’ve had on ancient life is too subtle to recognize in the fossil record. So it’s safe too say that even if Betelgeuse were to explode really soon, in your lifetime, it still isn’t close enough to pose much of a risk. One less thing to worry about!

This question originally appeared on Quora – the place to gain and share knowledge, empowering people to learn from others and better understand the world. You can follow Quora on Twitter, Facebook, and Google+. More questions:

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