Avery Schiff wrote:
Compared to other stars, our Sun is rather unremarkable. It is near the center of our classification scheme
, in the middle of its life
, and kind of a loner, forming without any companion stars. As it turns out, the Sun’s solitary status may have allowed for life on Earth. Plenty of past work, fiction
, has considered the possibility of life in multi-star systems, but today’s paper explores how the rotation and magnetic activity driven in a tight binary system
might be severely detrimental to the habitability of nearby planets.
At the heart of this problem is rotation. Stars form from gas falling inwards
under their own self gravity. In order to conserve angular momentum, all of that infalling gas needs to continue spinning, resulting in the characteristic rotation we see in protostellar disks
. As a result, all stars begin their life rotating. However, they don’t spin forever. Stellar winds carry away angular momentum, especially through magnetic braking
, causing the star’s rotation to slow down as it ages. The oldest stars are therefore spinning very slowly and we can reliably predict a star’s age
by its rotation period.
Unsurprisingly, if you add a second star, the picture becomes more complicated. At a sufficiently close range the stars begin to exert tidal forces
on each other. In extreme cases, the stars could even collide and merge
. For the purposes of this paper, the authors are especially interested in the case where tightly orbiting stars can replenish their angular momentum by sapping energy from the binary orbit. Such a process would cause the orbit to grow tighter and tighter as the stars spiral inwards. As shown in Figure 1
, this can result in models of stars that are kept rotating for longer or are even accelerated by quickly rotating companions. ...