Item — HN Reader

> That's hotter than the Hagedorn temperature, there could be some very interesting stuff going on.

Unfortunately it's not made clear in the article, but the temperature they quote is not an actual temperature, but instead a way of describing the specific intensity of the radiation. In this case the emission they're measuring is non-thermal (synchrotron emission), so the "brightness temperature" of the radiation field is not the same as the thermodynamic temperature. I'd put in a top-level comment about it too: https://news.ycombinator.com/item?id=17898224

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However, any matter in the way of the emissions would still reach something like that temperature, right? There's got to be some dust out there that's over the hagedorn temperature.

Not likely, since the intervening material probably lets most of the radio emission through. So the radiative coupling between the synchrotron emission and that material is too weak to raise the temperature by much (if any).

> There's got to be some dust out there that's over the hagedorn temperature.

Interstellar dust grains are thought to be destroyed at temperatures of 1500-2000 K (depending on composition). And their absorption cross-section for absorbing radio waves is fairly small.