The Oskar Klein Centre blog

Cosmology and a bit more

The Lithium problem. Primordial, cosmological or stellar?

Fabio Iocco is one of the Postdoc working within the OKC on Dark Matter. He is also interested in one of the puzzles keeping astronomers and cosmologists busy: the Lythium problem. Fabio has recently organized a conference dedicated to this mystery and he is getting ready to give the next OKC colloquium, this is why I asked him to tell us a bit more about this topic.

Credit: Belèn Roncoroni

Alright: the “Lithium problem”.
The “Cosmological” Lithium Problem.
The “Primordial” Lithium problem.
We all have heard about it since kindergarden, but would you bet 5000 SEK you know exactly what it is? I did not, so had to look it up. And here is what I have learned.
First of all, let’s play it fair: there’s two stable lithium isotopes, lithium-six and lithium-seven. In the last years it seemed both had problems, but we are talking about the bigger brother here, the one who has had problems for a longer time. Since 1982, 30 years ago -when my brother was born- there have been observations of lithium-seven in metal poor stars of the galactic halo. The most metal poor stars, the smallest mass, therefore the oldest stars to be around. Or at least a good approximation of a lot, a lot old. Ancient, pristine maybe. Ay, there’s the rub: “maybe”. Would you bet they were the first stars to be formed? I would not, but that’s another story. What matters here is that the stars were not the first generation, but the stuff in their atmosphere, what you observe when you take spectra of their surface may have been whatever had been produced “as far back in the past” as we could get with chemistry observations in our galaxy.
Read more…

The end for supermassive population III stars?

Snapshot showing fragmentation and multiple star formation in a medium of primordial composition (Clark et al. 2011)

Are the first stars really very massive? Some 10 years ago, the idea that the first, metal-free stars would be very massive, became popular. Simple theoretical arguments about radiative cooling and complex numerical simulations both seemed to point to the formation of metal-free stars of masses of several 100s solar masses. Because of their zero metallicity they were dubbed Pop III stars. Early simulations of their formation are commonly associated with Tom Abel and Volker Bromm. Read more…