[perihelions]

The "isotope" part is a mistake in the article. The writers heard "He II" and very reasonably wrote down "helium-2", and added some exposition about that (hypothetical) nuclear isotope. But they're in fact unrelated things: "He II" in this context is an ionization state of helium (the +1 state) -- not an isotope. What the research is observing is high-energy radiation from stars stripping electrons from helium atoms. No rare isotopes in sight!

[dang]

Thanks! I've revised the revision (which, for those who care, was "Light from a rare state of helium in a distant galaxy"). Does it work now?

[mikewarot]

well... that makes a lot of sense

I came here wondering how they knew the spectra of an isotope with a half life of 10^-9 seconds

[skykooler]

Also, spectra don't vary significantly by isotope - even with deuterium the difference is fractions of a nanometer of wavelength, which is not something detectable in astronomical spectra.