Neutron stars spin on their axis just like Earth spins on its axis. However, neu

Question

Neutron stars spin on their axis just like Earth spins on its axis. However, neutron stars spin very fast. Sometimes, neutron stars exhibit a “glitch”. A glitch is when they suddenly start rotating much faster than they were before. These glitches are thought to occur because of “starquakes”. A starquake is an earthquake on a star, but it doesn’t happen because of plate tectonics like earthquakes do. During a starquake, the neutron star suddenly shrinks in size (its radius becomes smaller.) Just like our angular momentum lab were we pulled the sliding block in towards the center of the rotating arm, the neutron star speeds up after a starquake. It has to because it’s moment of inertia changes and angular momentum has to be conserved. So, let’s see how much a neutron star speeds up when a starquake happens. a) Let’s use our 20km diameter 1.5x solar mass neutron star from earlier.

First, calculate this star’s current moment of inertia. You’ll need to look up the formula for moment of inertia of a sphere.

b) Now, the starquake just happened. Let’s say it caused the neutron star to shrink to a diameter of 19.5km. Calculate it’s new moment of inertia.

c) Let’s say the neutron star was initially rotating at 30,0000 RPM. RPM is “rotations per minute”, and yes, they really do spin that fast. Image the Missoula Valley spinning around 30,000 times every minute. That’s sort what’s going on here. How fast will the neutron star be rotating after the starquake? Your answer should be in RPM.

Explanation / Answer

Step 1 of

For a neutron star spinning on their axis we need to find (a) The moment of inertia of the star. (b) When the starquake has happened , it causes neutron star to shrink, so we need to find the new moment of inertia. (c) And also to find the speed of the neutron star rotating after the starquake.

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