The Threat From Stellar Explosions

Betelgeuse is harmless, but other stars going supernova could spell death for Earth.

betelgeuse ALMA.jpg
Betelgeuse (as seen here by the ALMA telescope) is going to blow sometime. It's just a question of when.

In a recent update to The Astronomer’s Telegram Edward Guinan and Richard Wasatonic from Villanova University reported on the puzzling dimming of the bright star Betelgeuse, the right “shoulder” in the Orion constellation.

Guinan and his student Scott Wacker started observing the star in 1981, and the work has been continued by Wasatonic since 1995. Betelgeuse, a red supergiant, has never been as faint as it is now. While it used to be the eighth or ninth brightest star in the sky, by early February it had dropped to the 21st or 22nd brightest, making Orion look odd. It also dropped in temperature by about 100oC, and in luminosity by about 25 percent since last September.

The question is whether this is a prelude to a supernova explosion, or just part of some natural fluctuation. About 700 light years from Earth, Betelgeuse is one of the nearest stars that could go supernova. If it did indeed explode, it would be nearly as bright as a full Moon. Its anticipated explosion could happen tomorrow, or 100,000 years from now.

Supernova explosions have been implicated in triggering mass extinctions on Earth, like the one that occurred 2.6 million years ago or the Permian-Triassic extinction 252 million years ago that was the most devasting to Earth’s biota, killing about 96 percent of all marine species and 70 percent of all terrestrial vertebrate species.

Luckily, Betelgeuse is no threat to Earth. Whenever it does explode, its deadly radiation will spread out equally in all directions, and by the time it reaches us it will be too weak to be of concern. But other supernova candidates, such as Wolf-Rayet stars, are far more dangerous. Some of these could emit a gamma-ray burst that funnels radiation very narrowly along the star’s rotational axis. If Earth is in the shooting line, the result could be devastating. The most notorious example of this kind of star, known as WR 104, is too far away to threaten Earth, but other, closer Wolf-Rayet stars like the one within the Gamma Velorium system could be a concern.

That’s why learning more about stars about to go supernova could be a lifesaver in the future. In the case of Betelgeuse, we’d get about an hour of advanced warning before the bright explosion, from neutrinos and gravity waves emitted before the shock reaches the star’s surface and visible light starts to rapidly increase.

It also would be good to keep an eye on Betelgeuse this summer, when it will be too close to the Sun for observations from Earth. Here’s one suggestion, from amateur astronomer Walter Webb: How about letting our spacecraft at Mars help out?