Testing Gravity Theories Using Stars
  Modified theories of gravity have received a renewed interest due to their
ability to account for the cosmic acceleration. In order to satisfy the solar
system tests of gravity, these theories need to include a screening mechanism
that hides the modifications on small scales. One popular and well-studied
theory is chameleon gravity. Our own galaxy is necessarily screened, but less
dense dwarf galaxies may be unscreened and their constituent stars can exhibit
novel features. In particular, unscreened stars are brighter, hotter and more
ephemeral than screened stars in our own galaxy. They also pulsate with a
shorter period. In this essay, we exploit these new features to constrain
chameleon gravity to levels three orders of magnitude lower the previous
measurements. These constraints are currently the strongest in the literature.
