On Saturday morning, networks took time to obsess over an Everest-sized asteroid passing some three million miles from Earth. That’s fifteen times the distance to the moon, though watching on NBC or ABC, you’d have a hard time knowing this, as that little fact went unmentioned. Instead, networks pulled out animations of apocalyptic collisions sprinkled with mentions of the end of the dinosaurs.
Really, news people, if you need to fill some time with oh-so-scary stories of potential doom from above, why not this one? “A moon-sized object will pass within a quarter million miles Earth today, coming so close that the gravitational force will raise sea levels over half the planet and even cause a measurable change in the shape of our world.” Use anytime you like.
But if you want to look a little further afield, there is a genuine astronomical puzzle that got a new wrinkle this week. Or rather, a new dent.
Betelgeuse is a very large star. A very, very large star. So large that were one of the more powerful figures from the Marvel pantheon to snatch the Sun from its position and drop in Betelgeuse, the red supergiant would cover the orbits of Mercury, Venus, Earth, Mars, and most of the asteroids. Even Jupiter would barely escape being part of the big red blob.
Even though it’s 700 light years away, that massive size helps make it the 11th brightest star in the night sky … most of the time. Because Betelgeuse is a variable star—one with a brightness that increases and decreases over time. In fact, it’s the most variable star visible to the naked eye. There are a couple of different cycles going on within Betelgeuse’s bright-dim cycle, but it has never been as dim as it is right now, not in all the time that people have been making careful observations.
The latest cycle of dimming began in October 2019. By January 2020, Betelgeuse was less than half as bright as it had been three months before. Which led to a lot of speculation that Betelgeuse was going to blow up. Big time. As in become a supernova.
It might seem that stars like Betelgeuse, with many times as much fuel as our Sun, would last much longer. That’s not the case. Red supergiant stars burn through their hydrogen supplies very rapidly, giving them a lifespan that’s a small fraction of our Sun’s. It’s entirely possible that Betelgeuse will go supernova soon, only ”soon” means in the next few thousand years. It really hasn’t demonstrated the behavior that astronomers expected to see before the big boom.
Only … it should have started getting brighter by now. This isn’t just the dimmest Betelgeuse had been since anyone was measuring, it’s also the longest period of staying dim.
So the European Southern Observatory took a look using the Very Large Telescope and this week they’ve published some results. Betelgeuse is so large, that unlike most stars it’s not just a point when viewed by a powerful telescope. It can be resolved as a disc. But what the VLT saw was not a disc. It was a … a mess. In images, the upper half of Betelgeuse looks fairly normal, but the lower half isn’t just dimmer, it’s lopsided; almost as if someone had taken a bite out of the massive star.
Has Betelgeuse really turned into a off-kilter blob? If so, it may represent the kind of instability that suggests the star really is going to pop its top sooner rather than later. But there are other possibilities. Maybe it’s got a case of supergiant sunspots. Or, maybe it’s that hot, fast-burning starts like Betelgeuse can throw off a good deal of dust, where dust is just tiny particles of material that isn’t hydrogen or helium. Clouds of this dust may be between Earth and Betelgeuse, blocking the view of part of the star and also decreasing its apparent brightness.
Betelgeuse at the beginning and end of 2019.
In fact, it’s possible that some of what has been taken as variability in Betelgeuse due to it’s nature as a red supergiant, has always been due to orbiting dust clouds. The only way to know is to make a lot more images.
Or it could blow. Which would be cool. Betelgeuse isn’t near enough to harm Earth from its death throes, but if it did become a supernova everyone in the northern hemisphere would be treated to quite a show. Betelgeuse would temporarily outshine the full moon and be easily visible in the day.
No matter how many time it makes the news, that explosion is very unlikely. But it is possible — unlike a collision between Earth and the asteroid that went past on Saturday.
