Beware the Undead: How Stars Become Vampires

It’s Halloween week, mwahahahahahahaha!!! Oof, was that too much? It seems like it might have been too much. I can’t help it, I love Halloween: the decorations, the foods, the costumes, the films, the whole vibe.

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Full confession, my choice of a Halloween blog post topic this year was heavily influenced by the fact that I recently re-watched a 1958 movie gem from Hammer Horror, The Horror of Dracula, starring the members of one of the film industry’s most epic bromances, Peter Cushing as Dr. Van Helsing and Sir Christopher Lee as Count Dracula. 

This film is a classic and that is a hill I will die on (and while you’re checking it out you should also see 1957’s The Curse of Frankenstein and 1959’s The Mummy to fully experience Cushing and Lee absolutely relishing being screen antagonists, but I digress), and it also has put vampires on my brain. And yes, there is a completely legitimate way for me to link vampires to space science, thanks to the phenomenon known as the vampire star. Read on…if you dare!

The Legend

Okay, first let’s briefly explore the concept of vampirism in myth and literature so that we can see why the concept of vampire stars is a perfect fit. There are many vampire or vampire-adjacent legends from cultures around the world, though today the main pop culture concept of the vampire (in the US and Europe anyway) is largely based on the 1897 novel Dracula by Bram Stoker.

Which is a great read, by the way. Just saying.

Anyway, that concept as written out by Mr. Stoker has the vampire as a creature that survives far beyond a normal lifespan by feeding on the blood of the living, becoming younger looking in the process of doing so. And, as it turns out, this is a pretty good description of what happens in certain kinds of star systems as well—minus the literal blood part, of course.

Zombie Vampires

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Many stars exist in systems with at least one other star. Loner stars like our Sun are actually way in the minority, with only about 15% of stars going through life on their own. And, as you’ll find in any large pool of relationships, some of those are of the May-December type and others are just straight up parasitically toxic. For stars, both of these dynamics can turn out destructive. 

Let’s look at the May-December ones first. That’s not actually an accurate term, because the odds are that the two stars were probably born around the same time, one was just bigger than the other and therefore burned out faster. As that bigger star goes through its final phases it will puff into a red giant, and if a companion is close enough it will get engulfed in the expanding layers.

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When those outer layers are flung away in the bigger star’s final death throe (this is a star not massive enough to supernova, for the record), what’s left of it is a white dwarf, a stellar remnant which you can kind of think of as a zombie star…which is definitely the topic of next year’s Halloween week post.  Meanwhile the companion star is still there and still fusing away. Only now it’s quite close to the white dwarf. Close enough for the dwarf to start feeding.

The white dwarf will begin to gravitationally pull material from the companion. It’s not blood, but it is vital material to the living star. And the white dwarf will just keep pulling stuff (gravity…it’s a killer) until it has accumulated a certain amount of its companion’s mass. Because that’s the thing about white dwarfs, you see—they may have died gently the first time but if they gain enough mass they die again, and this time they explode.

The white dwarf, having drained enough matter from its ever more anemic companion, will erupt in a Type 1a supernova. In most cases the force of the explosion will shred not only the white dwarf, but also the companion who gave so much to its draining partner. The vampire is slain, but it takes its victim with it.

Pure Vampirism

Then you have the kinds of stars that really lean into the Bram Stoker model of vampirism. The discovery of this type of stellar vampire happened when astronomers looked at region near the Milky Way’s center. It’s an area densely packed with stars, but old stars.

There’s not a lot of star-forming ingredients in this part of the galaxy, so you don’t see any young stars. That’s why diagrams of the Milky Way show the center looking reddish-yellow. Massive, hot, blue stars don’t live long and any that were born in this part of the galaxy have been dead a long time, leaving the slower-aging red and yellow stars.

So how to explain the shocking existence of what appear to be massive young stars in a region where they shouldn’t exist because they cannot be born?? They’re vampires, obviously!

With so many stars packed so densely together as they are in the galactic center, it’s easy for stars to get very close, even close enough to collide. When that happens, if one star happens to be more massive than the other, it will consume the smaller star, shredding it and incorporating all that lovely stellar gas into itself.

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This, of course, means that it becomes more massive. And more massive stars, in the are bigger, brighter, hotter than less massive stars. They are also, thanks to that fact that in the normal course of things these big stars live shorter lives, generally assumed to be younger than the less massive stars. By feeding on unfortunate neighbors, these stars become brighter and look younger than before they ate. They are rejuvenated, just like Dracula feeding off his hapless victims.

Of course, as we’ve already discussed, the more massive the star the shorter its lifespan. By eating their companions and regaining their youth, these vampire stars are actually speeding up their own ultimate demise. Ironic, actually.

Renfields

What’s Dracula without Renfield, his enthralled servant who seeks only to serve the undead Count? Well, actually, Dracula doesn’t really need Renfield, as the book eventually proves (sidenote: I find the 2023 comedy Renfield, with Nicolas Cage as a particularly unhinged version of Dracula, hilarious). But it turns out some vampire stars have wicked assistants of their own helping herd victims into their clutches.

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A study of these destructively vampiric systems that made use of data from the incredibly prolific and dearly missed Gaia Telescope (RIP) suggests that about 40% of them are not binary systems, but trinaries, with a third star lurking farther out. That’s a suspiciously high percentage if the presence of the third star in the system has nothing to do with the feeding process.

It could be that gravitational interactions between the third star and the victim star actually push the victim in closer to the vampire, allowing it to start feeding. In other words, these cataclysmic trinaries have a Renfield star bringing a Dracula star its next meal. One can only imagine Bram Stoker would be…can I say stoked, or is that too horrible a pun to let ride?

Happy Halloween

Obviously one can talk about these particular sorts of stellar interactions without bringing up the storied undead. These systems are, after all, driven not by a parasitic curse of bloodlust but by the very predictable forces of gravity and nuclear fusion reactions. 

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But, particularly at this time of year, isn’t it just way more fun to think of these feeding systems as cosmic Draculas, slowly yet inexorably sucking the lifeforce from hapless victims too firmly caught in their embrace to escape? Rather than thinking of a stellar collision adding enough mass to push the resulting merged star into a higher-mass stellar classification, isn’t it more fun to think of it as a powerful old star consuming the life of an unfortunate who strayed too close in order to regain its lost youth, even for a short while?

Scientifically accurate? Eh, not as much. But definitely more fun. Think of that as you look at the starry sky this All Hallow’s Eve. And, as always, may you have a wonderful, enjoyable, and safe Halloween.

And seriously, if you get a chance, check out The Horror of Dracula. Christopher Lee and Peter Cushing are having a grand old time!