Comment by gus_massa

Assuming it's not a fabrication of the press release, it may be jargon. Astrophysicists call "metal" everything that is not Hydrogen or Helium, but Chemist disagree heavily.

In this case, the paper don't call it "hot" but it says that 99.99% of the Hydrogen is ionized.

To ionize one Hydrogen you need 13.6eV. The average energy is temperature*k_Boltzmann. So if the temperature is 13.6eV/k_Boltzmann ~= 160000K then the 50% of the Hydrogen is ionized and 50% not ionized.

To get only 0.01% not ionized you need to increase the temperature, IIRC -log(0.01%)~=9 times.

So the temperature is ~1400000K. Unless I'm making an horrible stupid mistake, I agree it's hot.

(I may be missing the 4.7eV of the dissociation of H2 molecules into two H atoms, that would increase the temperature like a 40%.)