Signs of Possible Antistars Found in Fermi Data

Apr 30, 2021 | Daily Space, Physics, Stars

Signs of Possible Antistars Found in Fermi Data
IMAGE: Fourteen celestial sources of gamma rays (colored dots in this all-sky map of the Milky Way; yellow indicates bright sources and blue shows dim sources) may come from stars made of antimatter. CREDIT: Simon Dupourqué/IRAP

When you study astronomy, and people learn that you study astronomy, you get asked lots of questions along the lines of “Could there be antimatter stars?”, “Could there be antimatter galaxies?”, and “Could there be dark matter galaxies?” And while we think we have found galaxies made of dark matter, most of my colleagues have gone through life saying “No, there are not antimatter stars.” And we might be wrong. 

This is why we do science. We want to figure out what is real about the universe, and we recognize that we actually don’t know everything; we are just trying really hard to know everything. 

Now, there are two kinds of matter, and we’re really bad at naming things. So there is the stuff we’re made out of – electrons, neutrons, protons, regular matter. But all of these particles have an antimatter version. Neutrinos have an antimatter version. And if you’ve watched Star Trek, you know that controlled reactions with antimatter generate a ton of energy. This is because if you put a regular electron and its antimatter cohort – a position or antielectron – together they are going to combine into energy. It’s awesome and luckily doesn’t happen all the time. For the most part, when particles come together, the reactions aren’t right to release energy. Antimatter neutrinos are passing through you constantly. No big deal. 

For reasons we don’t know, our universe probably formed with equal amounts of matter and the oppositely charged but otherwise identical “has gravity working the same way, has mass working in the way” antimatter. It’s just that charge that is different. The universe probably formed with equal amounts of matter and antimatter, and then something went sideways, and we were left with a universe that is pretty much all matter. We thought that meant no antimatter stars. 

A group of astronomers has gone through the Fermi Gamma-ray Space Telescope’s data and discovered fourteen different flickering spots in the sky that give off flashes of gamma-ray light that is consistent with those fourteen sources being antimatter stars. How did this happen? No idea. Is this what actually happened? No idea. This is one of those times when you look at something, there are a variety of options, and one of them defies all expectations. So those fourteen flickers are consistent with antimatter stars. 

That means that somehow our universe had clumps of antimatter that survived in the midst of all the matter or managed to form later. Those clumps of antimatter collapsed down into stars and because matter and antimatter look identical in how they do fission and fusion and all those sorts of things, those stars would be shining just like any other star except when a bit of actual matter hits them just right… gamma-rays happen. 

Now, normally I would simply look at this research and say, “Huh. That’s cool.” And then set it aside. The reason I didn’t entirely do that today is that an experiment aboard the International Space Station captured evidence of random antimatter helium just kinda hanging out existing as helium atoms do, except it was antimatter helium. Antimatter. Helium. And the best way to explain that is if there are antimatter stars. 

Again, this could have an entirely different explanation. We do science to figure these things out, but the universe just keeps showing us that it is more creative than we are in coming up with theories. So we have two lines of evidence: random antimatter helium detected by the ISS experiment and fourteen sources of flickering light. 

If there are antimatter stars out there they probably aren’t common, or we’d see a whole lot more flickering. Based on the density of the kind of material that is hanging around and then would be hitting these antimatter stars, if they exist in the disk of our Milky Way, they’d only be one in every 400,000 stars. Because there is so much stuff floating hitting around that would be hitting them, they would be twinkling like Christmas lights but in gamma-rays. If however, they are super rare and they only exist in the outskirts, the halo of the galaxy, there could be as many as one in ten stars out there that are antimatter, and we just don’t see them because there is not a lot of stuff hitting them causing them to flicker. 

I’m still not saying we found them. I’m saying there is some cool stuff going on that we don’t understand, and one really weird explanation that I would never have expected to see is that there are antimatter stars. This work is published in Physical Review D by Simon Dupourqué, Luigi Tibaldo, and Peter von Ballmoos.

We’re going to follow this story, folks. I don’t know where it’s going to go, but that’s going to happen on another day.

More Information

IRAP press release

Constraints on the antistar fraction in the Solar System neighborhood from the 10-year Fermi Large Area Telescope gamma-ray source catalog,” Simon Dupourqué, Luigi Tibaldo, and Peter von Ballmoos, 2021 April 20, Physical Review D


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