D-3: The Tyrant

The following was written after many requests, and was originally published on the Stellaris forums.

Do not go gentle into that good night,
Old age should burn and rave at close of day;
Rage, rage against the dying of the light.

– Dylan Thomas
Throughout this series I’ve had a lot of requests. Some of them are for things I was going to cover anyway, like Gliese 667Cc. Some were for things I hadn’t planned to cover, like Pluto. Some I initially said no to and then changed my mind, like the Great Attractor.

None of them attracted as many requests as this one did. So let’s do it. Let’s talk about Betelgeuse.

(Image courtesy NASA)

The Crab Nebula is deadly, and if you go there you will die far too quickly for the death to be horrible. Sagittarius A* is beyond deadly and you won’t even get close to it without dying horribly. Wolf-Rayet 104 has a very slight chance of being exceedingly¬†deadly. Pluto is deadly in its own way, as is the gravity on Latham’s Planet and the icy cold of the dark side of Zarmina. Even the vast dust fields around Fomalhaut will kill you pretty quickly if you go there. But friends, these are weaksauce compared to Betelgeuse. Betelgeuse is the gold standard of things in space that hate you. When death came for Betelgeuse she wrestled him to the floor, kicked his ass and stole his crown.

Once upon a time, Betelgeuse was a main sequence star like any other, born in the enormous hydrogen nebulae of Orion’s Shoulder, wheremany stars are born and die. She was a big star, bright and blue and short-lived; and for reasons we’ll never know she decided that the best way to spend the few million years of her lifespan was to be violently catapulted out of Orion’s Shoulder and go wandering.

By “wandering” I mean she’s moving so fast that she’s got a bow wave. Space is mostly empty, but not quite: there are a few molecules scattered here and there across the vaccuum, and Betelgeuse is going fast enough that these are offering resistance. O-class stars don’t live long, but Betelgeuse didn’t plan to spend that time amongst her peers.

Not that she has peers.

Eventually, Betelgeuse burned through all her hydrogen. When that happened she swelled up into a giant, started fusing helium, and we can imagine that the galaxy breathed a sign of relief. Surely they were safe now? But no, death just made Betelgeuse angry. She didn’t even lose her blue colour, that’s how hot she was.

Eventually she burned through her helium too. Surely now she would go? Nope. You underestimate just how much Betelgeuse likes burning things. You probably can’t light ashes and smoke on fire: similarly, most stars can’t fuse oxygen and carbon. In this, we see that most stars just aren’t as committed to burning stuff as Betelgeuse is. She swelled up even further and started fusing oxygen. When she ran out of oxygen, she swelled up even further and started fusing yet heavier gases.

Around 100 BC, a Chinese astronomer noticed Betelgeuse and remarked that she was a beautiful yellow colour; so beautiful, in fact, that he proposed that she be used as the standard reference point for a yellow star.

A millenium later, Arab astronomers noticed Betelgeuse and remarked on her beautiful red colour. Not having read the work of their Chinese predecessor, they suggested that she be used as the standard reference for a red star. Her name comes from them: “Betelgeuse” is a corruption of the Arabic word for “a reddish colour.”

In between these two sightings, you might think that Betelgeuse cooled down: red stars are cooler than yellow stars, after all. However, you would be mistaken.

The Arabic astronomers noticed another puzzling thing, which also puzzled Europeans when we finally got our act together and stopped being so backwards: Betelgeuse changes luminosity drastically. She’s traditionally catalogued as the ninth brightest star, but she sometimes goes ashigh as seventh brightest and at other times diminishes to tenth. Many stars change like this, but they normally do so predictably and on a strict pattern. Betelgeuse is utterly unpredictable, sometimes changing in just days.

(Image courtesy NASA)

This isn’t because she hates us. Well, not just because of that. Most variable stars vary because they’re rotating and one side is darker than the other. Betelgeuse, by contrast, is doing it because she’s surrounded by a shroud of her own blasted-off, cooling outer layers. These extend out up to 30AU, which means that if she was in the Solar system they would reach the orbit of Neptune.

Because of her bow wave, sometimes this shroud of gas gets a little thinner, and then we see the hotter, angrier star below it, and we realise that Betelgeuse still burns with a hatred and a hunger that never went away.

(Image courtesy ESA / Herschel)

Even more frighteningly, occasionally a bubble of hot gas comes up from the layers close to her core and reaches the surface; and when this happens we realise that Betelgeuse is still blue on the inside. This whole “giant red star” thing is a costume she’s donned, a ruse to fool us into complacency.

Because of her unpredictability, there is no such thing as a safe distance from Betelgeuse. If you are orbiting her then she might kill you at any moment. If you don’t want to be killed at any moment, then stay away from her. Stay light years away from her. This is the only warning that you will get.


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