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"For instance, the mountains on the surface of the Crab pulsar could be as high as a few meters, while in PSR 1957+20 they cannot exceed a few microns!"

What's the reason for the difference? What causes one pulsar to be able to have mountains a million times as high as another?

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It's mostly due to the total mass of the star, since a more massive star has greater gravitational force at its surface, overwhelming the structural forces in the particles.

That doesn't sound right. Neutron stars vary by no more than a factor of two in mass; that's not enough to account for six orders of magnitude variation in height of highest mountains.

From my reading of it:

>The size of the highest mountain of order ∼ εR can be roughly estimated from the inequality (292).

>P, P˙ and I are, respectively, the pulsar’s period, period derivative and moment of inertia [in inequality (292)].

Those terms are all just multiplied together in the inequality, so changes in any of them could affect epsilon (the "dimensionless parameter characterizing deformations of the star")

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