... bi­nary stars can have so­lar sys­tems?

A so­lar sys­tem in which the plan­ets or­bit two stars sounds like pure science fic­tion. But bi­nary stars are said to ex­ist. Is this true?

Science Illustrated - - ASK US -

Not nearly all stars travel alone through space. At least half of all stars in the night sky have com­pan­ions and be­long to a sys­tem of two or more stars, which grav­ity main­tains in per­ma­nent or­bits around a com­mon cen­tre of grav­ity.

Within a dis­tance of 20 light years from the Sun, you will find 16 bi­nary stars and three triple stars. The Sun’s clos­est neigh­bour, Al­pha Cen­tauri, is a sys­tem of 3 stars, con­sist­ing of the 2 stars of Al­pha Cen­trauri A and B in close or­bit around each other and the more re­mote and weaker Prox­ima Cen­tauri.

Bi­nary stars are formed in the same cloud of gas and dust. So, they con­sist of the ex­act same el­e­ments and are the same age. But some­times they are born with dif­fer­ent masses, mean­ing that they develop dif­fer­ently and do not live for the same pe­riod of time. The star with the largest mass will die first.

Some sci­en­tists even as­sume that all stars, in­clud­ing our own Sun, are born as bi­nary stars. The Sun’s hy­po­thet­i­cal twin is called Neme­sis, and bil­lions of years ago, it en­tered a path that sent it far away from the So­lar Sys­tem. Ac­cord­ing to this the­ory, Neme­sis might still ex­ist some­where in the Milky Way. The twin is prob­a­bly a brown dwarf – i.e. a small, cold star that will never be warm enough to start a fu­sion process.

In the Ke­pler 47 star sys­tem 3,400 light years from the Sun, at least three plan­ets are or­bit­ing a spec­tro­scopic bi­nary star.

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