Ask Ethan: How Does Spinning Affect The Shape …

Ask Ethan: How Does Spinning Affect The Shape Of Pulsars?

“[S]ome pulsars have incredible spin rates. How much does this distort the object, and does it shed material this way or is gravity still able to bind all of the material to the object?”

If you spin too quickly, the matter on the outskirts of your surface will fly off. If you’re in hydrostatic equilibrium, your shape will simply distort until your equatorial bulge and your polar flattening result in the most stable, lowest-energy configuration. For our Earth, this means the best place to launch a rocket is near the equator, and our planet’s polar diameter is a little more than 20 km shorter than its equatorial diameter. But what about for the fastest-rotating natural object we know of: a neutron star. While most neutron stars rotate a few times a second, the fastest one makes 766 rotations in that span, meaning that a neutron on the surface moves at about 16% the speed of light. Much faster, and could it escape? Or, perhaps, is the pulsar’s shape highly distorted, either due to that rotation or to the incredibly strong magnetic fields inside? Neutron star matter is very different from anything we’re used to, so don’t bet on any of those.

Other than the first few fractions-of-a-second, changes to neutron stars are slow and mostly inconsequential. Come find out how bad it is on this edition of Ask Ethan!