Caffau’s star is sometimes called an “impossible star.” It’s actually just an interesting star that we don’t fully understand.
Chemodynamics
Much of the modeling of astrophysical systems focuses on dynamical behavior. That is, how stars, planets and interstellar clouds move under the forces of gravity. While such dynamical modelling can prove useful for studying the motion of galaxies, they are not quite as good at modeling the evolution of galaxies. That’s because galaxies evolve over time not only due to the motion of stars within them, but they also evolve chemically as old stars die and new stars form. The chemical makeup of new stars depends where and when they form.
Even Odds
In the early moments of the universe, hydrogen and helium were formed through a process known as baryogenesis. Trace amounts of other elements such as lithium were also produced, but none of the heavier elements. This means that the first generation of stars were composed of hydrogen and helium, and it is only through fusion in their cores that the heavier elements we see today were created. The carbon, oxygen and iron in our bodies was produced through that process, which is why it is often said that we are star stuff.
Testing Metal
When it comes to planetary systems, it’s generally been thought that planets would tend to form around stars with a higher metallicity. At a broad level that makes sense because rocky planets such as Earth can only form in a system where there are enough metals like iron, silicon, carbon and the like. You can’t make a terrestrial planet out of just hydrogen and helium. But now that we’ve discovered lots of exoplanetary systems, we can actually put this idea to the test. A recent paper in Nature has done just that, and they’ve found something rather interesting.
False Positive
Last year a paper in the Astrophysical Journal announced the discovery of two super-Earths orbiting a low metallicity Sun-like star known as HD41248. This was kind of a big deal, because it demonstrated that low metallicity stars could have rocky planets. Most of the known exoplanets are around higher metallicity stars. The two planets were discovered by observing the radial motion of the star (it motion toward or away from us) as measured by the Doppler shift of the starlight. Now a new paper in Astronomy and Astrophysics demonstrates that the planets likely don’t exist.
Second Generation
A new star has been discovered that was born from the very first stars of the universe. We can identify it by its particularly low metallicity.