According to the recently proposed “astronomical sandglass model” of the pulsed radio sources1 a pulsar is a neutron star at the critical mass limit for gravitational instability. Any loss of stability resulting in incipient collapse is quickly restored by the remaining nuclear resources, which, it was assumed, can still generate thermal pulses of about 1034 ergs. Because the radius of a critical neutron star is 106 cm, the resulting energy density is of order 1016 erg cm-3, corresponding to X-ray phonons. The degenerate interior of the star has a very high thermal conductivity and the X-ray pulse passes rapidly to the surface, where it blows off the thin (~1012 g) non-degenerate outer layer with less than escape velocity. After about a second this ejected material has all trickled back to the surface, triggering off the next instability.