Re: Newton's third law
Whenever I read about someone complaining about centrifugal force, I find myself wondering if the person in question knows as much as they claim.
Imagine holding a piece of string with a rock glued to the other end. The Earth's gravity pulls the rock down. The rocks gravity pulls the Earth up. The rock pulls down on the string and the string pulls up on the rock. The string pulls down on your hand and your hand pulls up on the string.
Spin the rock round in circles - you are providing a centripetal force that curves the rock's motion into a circle. The rock provides a centrifugal force pulling on your hand.
In the article, the spin of a neutron star increases because matter moves into a black hole in the middle. Gravity provides the centripetal force required to curve the motion of the outside of the neutron star into a circle. While the star holds together, there must be an equal an opposite force preventing collapse. That is centrifugal force provided by the spin. The spin increases until centrifugal force exceeds gravity, at which point the star breaks up.
Centrifugal force is an example of an inertial force (a force proportional to mass). From another (Einstein's) point of view, inertial forces are artifacts created by selecting an accelerating reference frame. Astronauts in a rocket with the engines on experience a force like gravity because they are in an accelerating reference frame. A motor cyclist riding inside a wall of death experiences a force like gravity because he is in an accelerating (rotating) reference frame. People on Earth think that they experience gravity, but gravity is an inertial force. Although you think you are sitting still in your arm chair, you are really in an accelerating reference frame. Centrifugal force is an inertial force that results from selecting an accelerating reference frame and is just as real/unreal as gravity.