In this article, Ron Cowen says that gas is where the action is since dark matter predominantly responds to only gravity. Because dark matter responds to gravity, wouldn’t it, like gas, be pulled into the star-making process and become part of the resulting star? Why is our sun not predominantly dark matter?

Eugene (Gene) Cater
Easley, S.C.

On the largest scales, the amount of dark matter is much greater than the amount of baryons—ordinary atoms. But on the scale of individual planets or stars, there is more ordinary matter. That’s because baryons can radiate away their energy (ridding them of heat that would fight gravity) and therefore clump more tightly under the influence of gravity than can dark matter (which can’t radiate), says theorist Piero Madau of the University of California, Santa Cruz. —Ron Cowen