Will Betelgeuse Kill Us?

Orion constellation - Betelgeuse

There are many myths surrounding the explosion of Betelgeuse, regardless of the time frame in which the star is anticipated to go supernova. Some say  it will be as bright as the full moon in the sky. Others take it a step further by suggesting it will outshine the Sun. Are these ludicrous statements, or do they have kernels of truth to them?

Supernovas are the most energetic events in the universe and, as a result, they are a notable threat to life. What are the chances of us being effected by an explosion so distant though?

The star Betelgeuse has appeared in African starlore and the popular constellation to which it belongs, Orion, has several traditional myths surrounding it. Appearing upside-down in the Southern Hemisphere, the Namaqua people of Southern Africa created stories about the prominent lion they saw in the night sky.

Most stars in constellations aren’t physically associated. The distances between these remote incandescent bodies can be vast. To put the full Orion constellation into perspective, let’s consider the distances of these stars from Earth:

  • Bellatrix is 240 light years distant
  • Rigel is 800 light years distant
  • Salph is 1305 light years distant
  • Betelgeuse is 640 light years distant

The speed of light is:

  • 299 792 458 m/s
  • 17 987 547 480 m/min
  • 1 079 252 848 800 m/h
  • 299 792 km/s
  • 17 987 547 km/min

Saying that Betelguese is 640 light years away means it would require a spaceship traveling at the speed of light 640 light years to get there. These distances are not enormous in astronomical terms, but are still staggering to consider nonetheless. It basically means that Betelgeuse is 6.05473818 × 1015 kilometres away from Earth.

Betelguese might not pose much of a threat to us because of its immense distance from us, but rumours of its imminent death are correct. Because we only see Betelgeuse as it was 640 years ago (it takes the light 640 years to reach us) we are seeing an outdated version of the star from around 1372 AD. In order for us to see it going supernova in 2012 that would mean it would have had to have exploded 640 years ago. It might have technically already gone supernova, or it might only go supernova in the next thousand years.

As we currently see it, it is a red giant, an aging star which is starting to run out of fuel and shed its outer layers, expanding and bubbling as it increases in size. If you look up at the night sky you will be able to see how red and luminous it appears in contrast to the stars around it.

Even though Betelgeuse won’t cause us any harm it will still be a spectacular event to witness. In 1054 AD a star in the Crab Nebula went supernova and was so bright the Chinese recorded that the event could be seen during the daytime.

Crab Nebula

“The star was so brilliant that it was visible even during the day for nearly three weeks and only faded from view nearly two years later.”

Phil Plait weighs in on how bright Betelgeuse would appear to us:

“At 600+ light years, a supernova would be pretty bright, but hardly bright enough to be a second Sun, as both articles say. Sorry, no Tatooine-like sunsets for us. It wouldn’t even be as bright as the full Moon, really, but certainly far brighter than Venus. Enough to cast a shadow, which would actually be pretty cool.”

So, all this fear about supernovas can’t be that unfounded. Well, it’s not. If a supernova were to explode close enough to do damage, that damage would be extensive and devastating. The gamma radiation would cause a chemical reaction in the Earth’s atmosphere, converting molecular nitrogen into nitrogen oxides and depleting the ozone layer enough to expose earth to harmful cosmic and solar radiation.

It’s possible that such an event has happened to Earth before, suggested as the cause for the Ordovician–Silurian extinction, which resulted in the death of nearly 60% of the oceanic life on Earth.

When Betelguese explodes it will be classified as a Type II Supernova. A star must have at least 9 times, and no more than 40–50 times, the mass of the Sun for this type of explosion. It is distinguished from other types of supernova by the presence of hydrogen in its spectrum.

A Type 1a Supernova is the violent explosion of a white dwarf star, a dying star which has ceased nuclear fusion. What’s dangerous about Type 1a Supernovas is that they sneak up on you, like hidden assassins. They are dim stars, hard to detect, and hard to study, meaning that whatever explosions will result from them will occur unpredictably.

The nearest, most likely threat is IK Pegasi, lying about 150 light years away, uncomfortably close. It was identified as a likely candidate by David Wonnacott, Barry J. Kellett and David J. Stickland in a 1993 paper.

It is a ticking time bomb, but in the time it will take for the IK Pegasi system to evolve to a state where a supernova could occur, it will have moved quite a bit further away from Earth, though it may still pose a threat. It’s possible that it could be 500 light years away in a few million years and may not even explode for 100 million years. Nevertheless, knowledge of these secret killers in our neighbouring universe, such as gamma ray bursts and Type 1a Supernovas, definitely makes the comparatively miniscule threat of Betelgeuse less of a concern.

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2 responses to “Will Betelgeuse Kill Us?

  • Paul

    I’m not sure if I want Betelgeuse to go nova in my lifetime or not. Would be spectacular event, but afterwards the Orion constellation would be missing an important part of it’s structure 😎 It’s fascinating to imagine if it’s already happened in the past 640 years…

  • Tijs

    a type IIa supernova has to be within 25-30ly to pose a direct threat, so we’re actually relatively safe…

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