Everybody’s been in a lather about one of the most famous stars in the sky. That would be Betelgeuse and its “mysterious” dimming or “fainting” that is catching astronomers’ attention. I’ve seen a lot of headlines about how scientists are perplexed or confused or whatever by this star losing some brightness. Even worse are the headlines about how it’s acting strangely, or that its behavior is very weird or that it’s about to explode.
So, I started digging around about it because whenever I see clickbait headlines, I know that somebody didn’t understand the astronomy. Turns out that Betelgeuse is pretty much acting as it has throughout its later life. That’s offering astronomers more insight into its late-stage behavior, which gives a peek at how old, massive stars age and eventually die.
Betelgeuse, which is the bright left “shoulder” of the constellation of Orion, is a variable star. That means it pulsates in brightness over time. It goes from being the eleventh-brightest star in the sky to being not even in the top twenty brightest stars. Right how, it is, in fact, the faintest it’s been more than a hundred years. Sounds pretty interesting, no? It certainly is if you’re a variable star researcher.
It turns out that Betelgeuse goes through several cycles of dimming and brightening over time. These are due to changes in size and temperature. It’s also possible that the current dimming is being caused by an outburst of material from the star that’s partially obscuring our view. A lot of stars “huff off” material as they age and that stuff creates a shell around the star. That would cause it to appear dimmer to us because some of the light is absorbed or blocked by the material in the shell.
Behavior of Cranky Old Stars
Apparently all of this is completely normal for Betelgeuse. It’s an aging supermassive star and objects like that are cranky as they get older. They oscillate and spew. And, eventually, they blow up. So, does all this dimming and mass loss mean that Betelgeuse is about to explode as a supernova? Probably not. Although, to be fair, going supernova IS the end state for this star. But, it’s not likely to happen for a while.
It might be as little as around a hundred thousand years before this aging red supergiant collapses in on itself and then bursts out as a supernova. Or it could take a bit longer. But, it’s not likely to be tomorrow. Or the next day. Or anytime soon. Kind of disappointing to those of us who’d like to witness a relatively nearby supernova in our lifetimes, but that’s the breaks.
What WILL happen when Betelgeuse gets to its bursting point? Its core will collapse when it runs out of fuel to sustain fusion reactions. The weight of all the layers of gas above it will cause them to crash in on the core. There will be a huge bounce (a rebound) and a lot of Betelgeuse’s material will burst out in a catastrophic explosion. That’ll spread “star stuff” throughout its neighborhood. It won’t all be gone, though. The heavily smashed core will remain, most likely as a neutron star. There won’t be enough mass for it to form a black hole, unfortunately. But, the fireworks show will be a great one, for our great-great-great^n grandkids. They’ll see it from Earth at a relatively safe distance of about 642 light-years.
Another Cranky Type of Star
While Betelgeuse grabs all the attention, another type of star IS going to explode by century’s end. It’s called binary star V Sagittae (V Sge), and it’s not just one star. It’s in a class of object called a “cataclysmic variable binary star”. V Sge has a rather ordinary star orbiting in a binary dance with a white dwarf star. The regular star is losing mass, which is falling onto the white dwarf. That action is powering a hugely powerful stellar wind, as well. Scientists have recently announced that this star is going to give us quite a light show by century’s end. At that point, it will become the most luminous star in the galaxy. It’ll be at least as bright as Sirius, which is currently the brightest star in our night-time sky. It’ll be quite the spectacle.
The action will start long before V Sge is set to explode. It won’t just flare up suddenly. We’ll have plenty of warning. Over the next decades, It will brighten up quite a bit. About the year 2083, the accretion of material from the normal star to the white dwarf will speed up. That will dump a LOT of material onto the white dwarf.
The fate of the normal star isn’t a good one. It will spiral in toward its white dwarf neighbor, losing more and more mass, which will cause them to brighten up. Eventually, the two stars will merge, and the final explosion will take place. What’s left will be a very massive white dwarf with a tightly packed core, and a vast envelope of burning hydrogen around it. The whole thing will be quite a show, and our great-grandkids will watch it from Earth at a very safe distance of about 8,000 light-years.