When Betelguese Blows

[Yazata]

Betelguese is a red supergiant star located about 590 light years from Earth. It's so large that if it took the place of our sun, its surface would be out around Jupiter's orbit. And its extremely active and variable, expanding and contracting such that its radius varies from around Earth's orbit to around Saturn's. It puts out about 120,000x the light of our sun. But despite being so big, it's not very dense, with a mass that's only 8 to 17 times that of the Sun. And it's losing mass, at the rate of about 3% of the Sun's mass every 10,000 years. Its nuclear fusion fires are dying and if those fires can no longer resist the force of gravity, at some point gravity will collapse Betelguese. It won't collapse into a black hole but into a really hot explosion.

It is expected to explode in what astronomers call a Type II Supernova. That will leave behind a neutron star about 1.5x as massive as the Sun that will become a pulsar. Nobody knows when this will happen, it might have already happened less than 590 years ago and it might not happen for several million years yet. But astronomers believe it's coming.

So, assuming that it happens tomorrow, or more accurately 590 years ago so that its prompt speed-of-light effects are just getting here now, what would the effects on the Earth be?

The core detonation will most likely generate a brief pulse of neutrinos that will reach Earth hours before we visibly see the star brighten. The neutrinos won't be noticeable without instruments since neutrinos interact so little with normal matter. But neutrino detectors in deep mine shafts that only occasionally detect a neutrino will suddenly detect millions of them. That will be the first alarm.

Betelguese will brighten for several weeks until it reaches a magnitude of about -12, which is about the same brightness as the full moon. It will cast shadows at night. All that light will be concentrated in a single point, that will be so bright that it will hurt to look at it and might cause retinal damage.

Of more concern are the x-rays and high-energy particles. These could be strong enough to cause mass extinctions on planets within a supernova's kill-zone of maybe 50 light years. But Betelguese is more than 10x that distance, so we should be ok. The radiation that arrives here will probably be too weak to get through the Earth's magnetic field and atmosphere, but spacecraft would need additional shielding for thousands of years. It might be hard on Moon bases.

A plasma shockwave will eventually arrive, thousands of years later. It's approach could be spectacular. The Crab Nebula is the remnant of a supernova that exploded some 960 years ago. It's also 6,500 light years away. But if it was Betelguese only 590 light years away, the Crab Nebula would be 14 times the diameter of the full moon in Earth's sky. After watching it approaching for thousands of years as it grows larger and larger but gradually fades to invisibility (except to instruments), its arrival will be an anticlimax, as the solar wind should be strong enough to deflect it. Although the nebula contains most of the mass of the exploded star, it's spread out over a huge volume, so it looks worse than it is. The inverse-square principle is our friend.

NASA photo of the Crab Nebula --

[Image: crab-nebula-mosaic.jpg]

[Zinjanthropos]

Well that should give my hypochondriac/germophobic brother a whole new array of illnesses to hide from. Regardless, I hope I’m alive to witness this event, another reason I feel fortunate to be a lump of matter that got a chance to look around, fantastic.

Just read an article that said human evolution may have been shaped by a past supernova. Said it may be the reason we walk upright but they didn’t elaborate. Anyone know anything about this?