Astronomers have known for some time that sunlike stars with high iron content are more likely to harbor planetary systems than other stars. Now they have a new clue- the amount of lithium. As we know from class, using spectroscopy we can determine the composition of faraway stars. So now we know that if a star has high iron and low lithium it is very likely to have planets. But why low lithium?
Garek Israelian, with the Instituto de Astrofisica de Canarias in Spain have analysed data from 133 sunlike stars. The leading explanation is that having planets around a newly forming star slows the rotation- and allows the lithium to sink lower into the core of the star where it can be consumed by fusion as part of the star's energy source. Without the drag of the planets, the star spins faster and the lithium stays near the surface, where temperatures are too low for lithium fusion to occur.
This is only true of sunlike stars near the middle of the main sequence on the H-R diagram. Small red stars always burn up their lithium quickly regardless of whether there are planets or not; large blue stars experience layering that prevents the mixing of the elements.
Posts
