Stars have a lifespan scaling as $1/M^{2.5}_\star$ for sunlike stars or more generally $t\sim 1/M^3$ for general stars (more or less), black holes have a lifespan (according to simple Hawking evaporation scenarios) of $t\sim M^3$. What we know about the lifetime span of neutron stars and black dwarfs? How do they (the time of life of those degenerate stellar systems) scale with mass? References would be welcome too!
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2$\begingroup$ An answer would require knowledge of proton decay or some other unknown mechanism. As far as we know, they are eternal. $\endgroup$– John DotyCommented Jan 7 at 23:37
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The standard reference, although it is getting a bit old, is (Adams & Laughlin 1997).
The main issue is that these objects either get absorbed by central black holes, or escape galaxies and then presumably evaporate due to proton decay. When this happens depends on particle physics issues. Their lifetime becomes proportional to their mass.
answered Jan 9 at 13:50
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$\begingroup$ When you say proportional to mass, are you saying that t~M (first power of mass)??? $\endgroup$ Commented Jan 10 at 15:18
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$\begingroup$ Yes. The decay rate makes the mass scale as $M_0 exp(-t/\tau)$ so whatever threshold endpoint mass you use the time until it is reached is $\propto M_0 \tau$. $\endgroup$ Commented Jan 10 at 15:28