The astronomers hoped to see proof of darkish matter particles in Betelgeuse. No luck

Axions are a hypothetical particle that could explain the existence of dark matter. But it can occasionally interact with normal matter, especially in the cores of stars. A team of physicists looked for evidence of axions in Betelgeuse and found nothing. It doesn’t mean the axion doesn’t exist, but it does mean it will be harder to find.

We don’t know what dark matter is. This is the name we give to the component of the universe that makes up 85% of the total mass. Whatever it is, it is a form of particle unknown to the Standard Model of Physics. It is also hardly allowed to interact with photons or normal matter, otherwise we would have seen it by now. There are many candidates for dark matter, and a family of candidate particles are known as axions, which are predicted in various theories of high energy physics.

At first glance, the Axion fits the bill, as it is small and light and almost never interacts with light or normal matter. Nearly. If the axion is of a certain type known as an “microlight” it may be detectable through a process known as the Primakoff effect. This effect needs a few ingredients to work. Occasionally, when a photon is embedded in a super strong magnetic field, it can decide to turn into an axion. This axion would then move where it wants, since it doesn’t really interact with anything else. When this axion hits another magnetic field, however, it can turn back into a photon, usually something high-energy like an X-ray that gives off a flash of light that betrays the existence of the axion and the Primakoff effect.

Stars have really strong magnetic fields in their cores, so they could be axion factories. And these axions can give off X-rays. We’d love to use our sun as a laboratory for this, but unfortunately it’s busy releasing all kinds of X-rays for reasons of its own, and so it’s hard to tell whether they’re coming from axions or something far less exotic.

But Betelgeuse is a different story. It’s a huge star towards the end of its life. It’s much cooler than the sun, so it hardly emits any X-rays. So if axions exist and the Primakoff effect is correct, Betelgeuse should be emitting a detectable amount of x-rays.

An MIT-based team of researchers did just that … and found squats. No x-ray. No signs of axions.

“Our results say that if you want to look for those really light particles that we were looking for, they don’t talk to photons a lot,” says Kerstin Perez, assistant professor of physics at MIT. “We basically make everyone’s life harder because we say, ‘You’re going to have to think of something else that would give you an axion signal.'”

These results do not completely exclude the existence of axions. It just means that if they are ultralight, their ability to convert to photons and vice versa must be very low. In fact, using Betelgeuse alone, these results place limitations on this ease of transition that are three times greater than any laboratory experiment.

So we’ll keep hunting.

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