When I first read about the star system WR 104, the hair on the back of my neck stood up.

I had just finished writing my book Death from the Skies!, and had a whole chapter in it about gamma-ray bursts (or GRBs), which are among the single most energetic and violent explosions the cosmos has to offer. They’re like a supernova concentrated down into focused death rays, so ridiculously luminous we can see them from clear across the observable Universe.

In my book I mentioned that there are likely no potential GRBs aimed at us that were close enough to hurt us, though.

Then I found out about WR 104. It’s a weird system, a binary star composed of two very scary high-mass stars, one of which could possibly be a GRB progenitor, and there was reason to believe it could be aimed directly at us! From 8,000 light-years away the damage shouldn’t be too much, but still, yikes. I’d rather not have one anywhere in the galaxy aimed at us. I wrote about all this for Discover Magazine, which at the time was hosting my BA Blog (cute historical context: this was in 2008, and I was concerned that embedding a 400 kB image file would be too big for the server).

Why did we think it might be aimed at us? Because of a bizarre structure surrounding the two stars: a dusty spiral arm that extends for a long way, and appears to spin around them.

Here’s an animation consisting of several observations of the system — mind you, these are real observations!

WHOA. These observations were taken using the Keck Observatory and were done in the infrared. What you’re seeing is complicated, but in a nutshell the two stars orbit each other every 241 days. They both emit powerful winds of material from their surfaces, which collide with each other to create dust — grains of carbon and hydrocarbons (think of it as soot). This material is warm and glows in the infrared, which is what Keck is designed to see, and gets thrown out from the stars like water from a rotating lawn sprinkler. The material isn’t actually spinning; each molecule from the winds is thrown directly away from the stars. But the direction they get thrown changes over time in a circular pattern, creating the illusion of a rotating spiral.

Science Stories You Can’t Get Anywhere Else

Feed your curiosity with Nautilus — a science newsletter for thinkers, seekers, and the endlessly curious. Each week, we bring you beautifully written stories at the intersection of science, philosophy, and culture. From the physics of time to the psychology of awe, our essays, interviews, and ideas dive beneath the surface and linger in the mind.

Join a global community of readers who believe that big questions deserve thoughtful answers. Whether you're a lifelong learner or just love a good mystery of the universe, Nautilus will challenge how you see the world — and maybe even yourself.

Sign up now and start thinking deeper.

Sign up today

I actually wrote about this in detail for a similar binary system called WR 140 (note the confusingly similar names) for my weekly column in Scientific American that explains how all this works, as well as in BAN Issue #828.

When you look at the pattern in WR 104, it really looks like you’re seeing it face-on, such that the plane of the spiral is perpendicular to us. And that’s the problem! It’s likely the two stars are aligned such that their rotation axes are parallel, and the material thrown out from their equators. That means the poles of the stars are aimed right at us. But when a star explodes as a GRB, the beamed material shoots directly away from the pole. That means that should the exploding star go all GRB on us, we’re looking right down the barrel of it.

Gulp.

But fear not! Probably!

A new paper has just been published questioning this idea [link to journal paper]. The author used very carefully taken observations of WR 104 to try to understand the properties of the stars and their winds. While the observations were done again with Keck, for this work he took spectra, breaking the incoming light into hundreds or thousands of individual colors. Different elements in the stars and wind emit light at very specific wavelengths, so a spectrum can tell you a lot about what material is seen.

More importantly, though, it can yield information on aspects like the velocity at which the two stars orbit each other; this motion induces a Doppler shift in the spectrum that can be measured (the shift incurred as the stars move toward and away from us as they orbit each other). He finds they orbit one another at about 60 kilometers per second, which is fast.

But that also tells us the mass of the two stars! The more massive they are, the faster they orbit. This gets complicated because finding the mass also involves knowing the distance and other factors, but an important one is what angle we view the system at. If we see the orbit edge-on then the Doppler shift is maximized. If we see it face-on then we should see no Doppler shift — we need to see motion toward or away from us to get a Doppler shift, and if we see the orbit face-on there is none.

That’s critical. If we assume the orbit is edge-on to us, then a simple plug and chug gives us the stars’ masses. But if it’s tilted then we see a smaller Doppler shift for that same mass! No matter how massive the stars are, we see no Doppler shift if they’re face-on. That means there’s a trigonometric sine dependence on the masses we find (if you don’t remember your trig, that’s fine, I’m just mentioning it here). In the end this means that the mass we get for the stars depends on the tilt of the orbits, and if the tilt is nearly edge-on the masses have to be a lot bigger to get the observed Doppler shift.

And now, finally, we get to the cool part. The assumption has been that the orbit is nearly face-on due to the shape of the spiral dust pattern. But in the new paper, the author shows that this gives unreasonably huge masses of the stars: 217 and 584 times the Sun’s mass! That’s basically impossible; the Universe can’t make stars that massive (at least, not today).

He argues that the masses are likely much smaller, more like 30 times the Sun. in that case, the orbit could be inclined by as much as 45° to us.

And if that’s the case, then the potential GRB is no longer aimed at us. Phew!

Assuming he’s right. There’s still a bit of uncertainty to all this, because the stars are a mess, and the wind blasting out material confuses the observations as well. I’d love to see JWST images and spectra of WR 104, since they would be much clearer.

Space is full of danger, but it looks likely that it has one less than we thought. I’ll add that we know for sure and for real both of the stars making up WR 104 will explode as supernovae, but probably not for hundreds of thousands if not millions of years. And it’s not clear if one will become a GRB or not. So we’re safe not only in space but in time, too.

That’s cool. Exploding stars are fascinating and well worth studying (I’ve studied a couple myself back in the day), and to be honest I’d prefer it if the study were more academic rather than feeling like I’m sitting in a room with a ticking bomb next door.

You can email me at [email protected] (though replies can take a while), and all my social media outlets are gathered together at about.me. Also, if you don’t already, please subscribe to this newsletter! And feel free to tell a friend or nine, too. Thanks!