When considering a spin rate of 1,122 revolutions per second, has anyone determined the diameter of the neutron star XTE J1739-285? If, for example, it were the same diameter as Earth, it would be traveling far in excess of the speed of light at its equator. In order to remain within the limitations of the speed of light its diameter would have to be less than a hundred miles!

R.G. Paul
Upland, Calif.

What is the maximum rate before the star flies apart from the rotation forces?

Sean Walton
Orem, Utah

The speed of light would limit the star to a 43-kilometer radius, says astronomer Phil Kaaret of the University of Iowa in Iowa City. He adds that there’s little surprise in that, since the expected radii of neutron stars are in the range of 10 to 20 km. The maximum rotation rate would be between 1,000 and 2,000 rotations per second, depending on the properties of the ultradense matter in the star, says Kaaret. —R. Cowen