Main Sequence Mass-Radius Relationship

The mass-radius relation is fairly tight for stars with M_* < 0.9 M_sun, but large at higher mass because of evolution on the Main Sequence. Define R ∝ M^α

Mass	Exponent, α
0.2-1.4	0.9
1.4-30	0.6

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The mass-radius relation implies that

<ρ> ∝ M^1-3α

===> stars are less dense with increasing mass, M.