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What Is an Antistar?

Leonard Kelley holds a bachelor's in physics with a minor in mathematics. He loves the academic world and strives to constantly explore it.

Antimatter operates like normal matter but has the opposite charges of our normal matter counterparts. Because of this, when they meet, they completely convert to light, and energy is released. This implies a symmetry of sorts, and yet we seem to exist in a Universe dominated by matter.

For unknown reasons, it seems as though an imbalance from the formation of the Universe has led to matter being everywhere with only traces of antimatter seen anywhere and usually as a result of some cosmological event creating it. No signs of ancient antimatter have been seen, but if it is out there, then the best chance of it surviving to this day is in the form of an antistar.

Why an Antistar?

No one really took antistars to be a serious possibility. For starters, matter should have annihilated any ancient antimatter by now, and if enough antimatter was present to form a star, then such an annihilation would have been very easy to spot, yet no such event has ever been seen. And antistars would look exactly like normal stars because all the mechanics are the same. Particles may have opposite charges, but that doesn’t impact stellar mechanics, so visually, all stars would look the same, and hoping to differentiate an antistar would seem hopeless (Sutter, Sapunar, Crane).

Then research was released by Simon Dupourque, Luigi Tibaldo, and Peter von Ballmoos, who looked at data from the Fermi Large area Telescope. Out of the then 5,787 gamma-ray sources spotted by it, 14 remained unaccounted for. If these are antistars, then it would place about 1 antistar for every 400,000 normal ones in our galaxy. Of course, the data needs more backing, and potential errors need to be parsed out before we can give full confidence in these results (Crane, Sapunar, Cooper).

But then some interesting data was found that have the trail some new life. The Alpha Magnetic Spectrometer, located on the International Space Station, has found up to 8 antihelium detections over its operation. The easiest method which would allow enough antihelium to be made and reach us would be an antistar, but it’s not the only possible route to make it (Crane, Sapunar, Cooper).

Other Alternatives

One option is the spallation process, in which high-energy cosmic rays collide with interstellar gas particles and create antimatter. But out of all the antihelium spotted, 6 of them were antihelium-3, something that could be made via spallation but is unlikely. The other 2 were antihelium-4, which is virtually impossible to be made under this process. Instead, it could have been from dark matter particles annihilating one another, but since we are not even sure about the makeup of dark matter, this is a chase in the dark, and even if it could happen, it still struggles with the antihelium-4 (Sapunar).

Are antistars hidden in plain sight?

Are antistars hidden in plain sight?

But How Could They Survive?

If all other possibilities don’t pan out, then we need to think about how antistars could exist in a matter-dominated Universe. Perhaps in the early Universe, discrete packets of antimatter were spread out fast enough during inflation to avoid interacting with matter. These then became their own antigalaxies on a small scale. This is because if they were built big, then a collision with a normal galaxy would create quite the reaction that we should have seen by now.

Instead, our antigalaxies could be more like globular clusters, where we have millions of stars instead of billions. They would be red because of their age, being from the early Universe, and the clusters wouldn’t have much gas or dust. This could even imply that a globular cluster full of antistars could pass through a matter galaxy with no or minimal interactions due to the low density of objects (and generally large distances between things).

If all of this is possible, then the antistars, though known mechanisms, could release antimatter, like through stellar wind, coronal mass ejections—even supernovas. And with matter-antimatter annihilations producing weak gamma rays of 70MeV, this could lead to a detectable trace of antistar activity (Crane, Sutter, Cain, Sapunar)

And really, what would it be like to find a new door in exploring the Universe?

Works Cited

Cain, Fraser. “Are there antimatter galaxies?” phys.org. Phys.org, 10 Jun. 2016. Web. 12 Jan. 2022.

Cooper, Keith. “Are antimatter stars firing bullets of antihleium at Earth?” physicsworld.com. IOP Publishing Ltd., 02 May 2021. Web. 12 Jan. 2022.

Crane, Leah. “Antistars may be lurking close by.” New Scientist. New Scientist, 01 May 2021. Print. 16.

Sapunar, Leto. “Stars Made of Antimatter Might Be Lurking in the Universe.” Scientificamerican.com. Springer Nature America, Inc., 07 Jun. 2021. Web. 12 Jan. 2022.

Sutter, Paul. “Could there be a cluster of antimatter stars orbiting our galaxy?” space.com. Future US, Inc., 08 Feb. 2021. Web. 12 Jan. 2022.

© 2022 Leonard Kelley