RE: https://mastodon.nl/@pi9rd/115763660927597618
There's a red giant star near the end of its life that's pulsing about every 4 years. It's spewing out a lot of gas with each pulse. The gases include hydroxyl ions (OH), carbon monoxide, sulfur oxides, and vaporized silica, magnesium and iron. When they cool, these chemicals combine to form magnesium-iron silicates. In short, DUST!
So much dust enshrouds this star that we can barely see it! Instead, we see the infrared radiation from the hot dust.
But more interestingly, we see microwaves, because this star is a natural maser!
A maser is like a laser with microwaves instead of visible light. Masers came first - and MASER means "Microwave Amplification by Stimulated Emission of Radiation".
How does it work?
Near this star, hydroxyl ions get excited to a higher energy state by being blasted with infrared radiation. When they fall down to a lower energy state, they emit photons of a particular energy. But thanks to some quantum mechanics discovered by Bose and Einstein, these photons lure *other* hydroxyl ions to fall down from the higher energy state - thus creating *more* photons of exactly this energy. We get a blast of photons all wiggling in synch with each other.
You should imagine about 100,000 hydroxyl ions per cubic centimeter doing this. That sounds like a lot, but it's actually close to a vacuum. They're about 100-1000 AU from the star, bathed in infrared light that's about 1/10 as bright as the Sun is here. The microwaves they emit are much weaker, but still remarkable.
This star goes by the dull name OH26.5+0.6, because it's an 'OH maser' star - it's not the only one - and its galactic coordinates are longitude 26.5°, latitude +0.6°.
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